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#REDIRECT [[Lecture_-_Fertilization]]
= Cell Division and Fertilization =
= Cell Division and Fertilization =


This lecture will introduce two key concepts of biology, cell division and cellular sexual development. Both these concepts will also be explored further in the Thursday laboratory.
This lecture will introduce two key concepts of biology, cell division and cellular sexual development. Both these concepts will also be explored further in the Thursday laboratory.


--[[User:MarkHill|MarkHill]] 15:44, 27 July 2009 (EST) Lecture notes in preparation (notice removed when complete)
'''Textbooks'''
* The Developing Human: Clinically Oriented Embryology (8th Edition) by Keith L. Moore and T.V.N Persaud - Chapter 2
* Larsen’s Human Embryology -  Chapter 1
 
 
'''Lectopia Lecture Audio''' Lecture Date: 28-07-2009 Lecture Time: 12:00 Venue: BioMed E Speaker: Mark Hill [http://lectopia.elearning.unsw.edu.au/ilectures/ilectures.lasso?ut=153&id=48835 Cell Division and Fertilization]


[[2010_Lecture_2|2010 Lecture -  Cell Division and Fertilization]]


===Cell Cycle===
===Cell Cycle===
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* [http://www.nature.com/celldivision/milestones/index.html Cell Division Milestones], Recent Nobel Prizes
* [http://www.nature.com/celldivision/milestones/index.html Cell Division Milestones], Recent Nobel Prizes


Features 2 mechanical processes
'''Features Two Mechanical Processes'''
* Mitosis segregation of chromosomes and formation of 2 nuclei  
* Mitosis - microtubule based segregation of chromosomes and formation of 2 nuclei  
* Cytokinesis splitting of the cell as a whole into 2 daughter cells
* Cytokinesis - microfilament based splitting of the cell cytoplasmic contents as a whole into 2 daughter cells


* Mitosis occurs in all cells, producing genetically identical progeny.
'''Features Two Types'''
* Meiosis occurs only in germ cells (sperm=spermatozoa and egg=oocyte), producing genetically different progeny.
* Mitosis - occurs in all cells, producing genetically identical progeny.
* Meiosis - occurs only in germ cells (sperm=spermatozoa and egg=oocyte), producing genetically different progeny.
** progeny = daughter cells, offspring
** progeny = daughter cells, offspring


===Cell Changes===
===Cell Changes===
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==Mitosis==  
==Mitosis==  
[[Image:Mitosis_fl.jpg|thumb|Fluorescent image of Mitotic spindle and chromosomes]]
[http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mcb.figgrp.5500 MCB Movie - The stages of mitosis and cytokinesis in an animal cell]
* Based on light microscopy of living cells light and electron microscopy of fixed and stained cells  
* Based on light microscopy of living cells light and electron microscopy of fixed and stained cells  
* 5 Phases - prophase, prometaphase, metaphase, anaphase, and telophase  
* 5 Phases - prophase, prometaphase, metaphase, anaphase, and telophase  
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* Chromosomes begin condensing  
* Chromosomes begin condensing  
* Chromosome pairs (chromatids) held together at centromere  
* Chromosome pairs (chromatids) held together at centromere  
* Microtubules disassemble  
* Microtubules disassemble  
* Mitotic spindle begins to form  
* Mitotic spindle begins to form  
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===Prometaphase===
===Prometaphase===
 
[http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mcb.figgrp.5509 MCB Movie - Centromeric attachment of microtubules] |
* Microtubules now enter nuclear region  
* Microtubules now enter nuclear region  
* Nuclear envelope forms vesicles around mitotic spindle  
* Nuclear envelope forms vesicles around mitotic spindle  
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===Metaphase===
===Metaphase===
 
[[Image:Mitosis_fl.jpg|thumb|Metaphase fluorescent image of Mitotic spindle and Chromosomes]]
* Kinetochore MTs align chromosomes in one midpoint plane  
* Kinetochore MTs align chromosomes in one midpoint plane  
* Metaphase ends when sister kinetochores separate
* Metaphase ends when sister kinetochores separate
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==Meiosis Differences==
==Meiosis Differences==
===Female - Oogenesis===
===Female - Oogenesis===
[http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=cooper.figgrp.2492 Figure 14.37. Meiosis of vertebrate oocytes]
[http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=cooper.figgrp.2492 The Cell - Figure 14.37. Meiosis of vertebrate oocytes]
* Meiosis initiated once in a finite population of cells  
* Meiosis initiated once in a finite population of cells  
* 1 gamete produced / meiosis  
* 1 gamete produced / meiosis  
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===Male - Spermatogenesis===
===Male - Spermatogenesis===
[http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mboc4.figgrp.3734 MBoC - Figure 20-27. The stages of spermatogenesis]
* Meiosis initiated continuously in a mitotically dividing stem cell population  
* Meiosis initiated continuously in a mitotically dividing stem cell population  
* 4 gametes produced / meiosis  
* 4 gametes produced / meiosis  
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==Abnormalities==
==Abnormalities==
[[Image:Trisomy21arrow.gif]][[Image:trisomy21female.jpg|300px]][[Image:trisomy21female.jpg|300px]]
[[Image:Trisomy21arrow.gif]][[Image:trisomy21female.jpg|300px]][[Image:trisomy21male.jpg|300px]]


* The most common chromosome abnormality is '''aneuploidy''', the gain or loss of whole chromosomes.  
* The most common chromosome abnormality is '''aneuploidy''', the gain or loss of whole chromosomes.  
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**  oocyte ovulation and release with associated cells,  from ovary into fimbria then into uterine tube (oviduct, uterine horn, fallopian tube) and epithelial cilia mediated movement.
**  oocyte ovulation and release with associated cells,  from ovary into fimbria then into uterine tube (oviduct, uterine horn, fallopian tube) and epithelial cilia mediated movement.
** spermatozoa ejaculation, deposited in vagina, movement of tail to "swim" in uterine secretions through cervix, uterine body and into uterine tube, have approximately 24-48h to fertilize oocyte.
** spermatozoa ejaculation, deposited in vagina, movement of tail to "swim" in uterine secretions through cervix, uterine body and into uterine tube, have approximately 24-48h to fertilize oocyte.
[http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=endocrin&part=A972&rendertype=box&id=A1230 Endocrinology - Diagram of the comparative anatomy of the male and female reproductive tracts]


===Oogenesis===
===Oogenesis===
[http://embryology.med.unsw.edu.au/Notes/week1_3a.htm Week 1 - Oogenesis]
[[Image:Ovary5x.gif|thumb|Histology of the Ovary]]
[[Image:Ovary5x.gif|thumb|Histology of the Ovary]]
[[Image:Ova41he.jpg|thumb|Preantral Follicle]]
[[Image:ova20he.jpg|thumb|Antral Follicle and Oocyte]]
* Process of oogonia mature into oocytes (ova, ovum, egg)  
* Process of oogonia mature into oocytes (ova, ovum, egg)  
* all oogonia form primary oocytes before birth, therefore a maturation of preexisting cells in the female gonad, ovary  
* all oogonia form primary oocytes before birth, therefore a maturation of preexisting cells in the female gonad, ovary  
[[Image:Oocytenumber.jpg|300px]]
* humans usually only 1 ovum released every menstrual cycle (IVF- superovulation)  
* humans usually only 1 ovum released every menstrual cycle (IVF- superovulation)  
* oocyte and its surrounding cells = follicle  
* oocyte and its surrounding cells = follicle  
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====Ovulation (HPG Axis)====
====Ovulation (HPG Axis)====
[[Image:XXhpgaxis.gif|thumb|HPG Axis]]
[[Image:XXhpgaxis.gif|300px|HPG Axis]]
* Hypothalmus releases gonadotropin releasing hormone (GRH, luteinizing hormone–releasing hormone, LHRH) -> Pituitary releases follicle stimulating hormone (FSH) and lutenizing hormone (LH) -> ovary follicle development and ovulation.
* Hypothalmus releases gonadotropin releasing hormone (GRH, luteinizing hormone–releasing hormone, LHRH) -> Pituitary releases follicle stimulating hormone (FSH) and lutenizing hormone (LH) -> ovary follicle development and ovulation.
** release of the secondary oocyte and formation of corpus luteum  
** release of the secondary oocyte and formation of corpus luteum  
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====Zona Pellucida====  
====Zona Pellucida====  
[http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mboc4.figgrp.3722 MBoC - Figure 20-21. The zona pellucida]
* glycoprotein shell ZP1, ZP2, ZP3  
* glycoprotein shell ZP1, ZP2, ZP3  
* mechanical protection of egg  
* mechanical protection of egg  
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* block of polyspermy  
* block of polyspermy  
** altered to prevent more than 1 sperm penetrating  
** altered to prevent more than 1 sperm penetrating  
** may also have a role in development of the blastocyst  
** may also have a role in development of the blastocyst


====Corona Radiata====  
====Corona Radiata====  
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===Gamete formation- Spermatogenesis===
===Gamete formation- Spermatogenesis===
[http://embryology.med.unsw.edu.au/Notes/week1_3b.htm Week 1 - Spermatogenesis]
* process of spermatagonia mature into spermatazoa (sperm)  
* process of spermatagonia mature into spermatazoa (sperm)  
* continuously throughout life occurs in the seminiferous tubules in the male gonad- testis (plural testes)  
* continuously throughout life occurs in the seminiferous tubules in the male gonad- testis (plural testes)  
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Fertilization - Spermatozoa  
Fertilization - Spermatozoa  
* '''Sperm Binding''' - zona pellucida protein ZP3 acts as receptor for sperm  
* '''Sperm Binding''' - zona pellucida protein ZP3 acts as receptor for sperm  
* '''Acrosome Reaction''' - exyocytosis of acrosome contents (Calcium mediated)  
* '''Acrosome Reaction''' - exyocytosis of acrosome contents (Calcium mediated) [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.figgrp.3741 MBoC - Figure 20-31. The acrosome reaction that occurs when a mammalian sperm fertilizes an egg]
** enzymes to digest the zona pellucida  
** enzymes to digest the zona pellucida  
** exposes sperm surface proteins to bind ZP2  
** exposes sperm surface proteins to bind ZP2  
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Fertilization- Oocyte
Fertilization- Oocyte
* '''Membrane Depolarization''' - caused by sperm membrane fusion, primary block to polyspermy  
* '''Membrane Depolarization''' - caused by sperm membrane fusion, primary block to polyspermy  
* '''Cortical Reaction''' - IP3 pathway elevates intracellular Calcium, exocytosis of cortical granules  
* '''Cortical Reaction''' - IP3 pathway elevates intracellular Calcium, exocytosis of cortical granules [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.figgrp.3743 MBoC - Figure 20-32. How the cortical reaction in a mouse egg is thought to prevent additional sperm from entering the egg]
** enzyme alters ZP3 so it will no longer bind sperm plasma membrane  
** enzyme alters ZP3 so it will no longer bind sperm plasma membrane  
* '''Meiosis 2''' - completion of 2nd meiotic division  
* '''Meiosis 2''' - completion of 2nd meiotic division  
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====Formation of the Zygote====  
====Formation of the Zygote====  
 
[[Image:Early zygote.jpg|thumb|Early human zygote showing Pronuclei]]
* Pronuclei - Male and Female haploid nuclei approach each other and nuclear membranes break down  
* Pronuclei - Male and Female haploid nuclei approach each other and nuclear membranes break down  
* chromosomal pairing, DNA replicates, first mitotic division  
* chromosomal pairing, DNA replicates, first mitotic division  


* Sperm contributes - centriole which organizes mitotic spindle  
* Sperm contributes - centriole which organizes mitotic spindle  
* Oocyte contributes - mitochondria (maternally inherited)  
* Oocyte contributes - mitochondria (maternally inherited)


====Sex Determination====  
====Sex Determination====  
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== References ==
== References ==
===Textbooks===
* '''The Developing Human: Clinically Oriented Embryology''' (8th Edition) by Keith L. Moore and T.V.N Persaud - Chapter 2
* '''Larsen’s Human Embryology''' by GC. Schoenwolf, SB. Bleyl, PR. Brauer and PH. Francis-West -  Chapter 1
===Online Textbooks===
===Online Textbooks===
* '''Developmental Biology''' by Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000[http://www.ncbi.nlm.nih.gov/books/bv.fcgi?highlight=meiosis&rid=dbio.figgrp.200 Figure 2.9. Summary of meiosis] | [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=dbio.figgrp.1360 fusion of egg and sperm plasma membranes]
* '''Developmental Biology''' by Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000[http://www.ncbi.nlm.nih.gov/books/bv.fcgi?highlight=meiosis&rid=dbio.figgrp.200 Figure 2.9. Summary of meiosis] | [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=dbio.figgrp.1360 fusion of egg and sperm plasma membranes]
* '''Molecular Biology of the Cell''' 4th ed. Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter New York and London: Garland Science; c2002 - IV. Internal Organization of the Cell Chapter 17. The Cell Cycle and Programmed Cell Death [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mboc4.chapter.3167 Programmed Cell Death] |  [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mboc4.section.3169 An Overview of the Cell Cycle] | [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mboc4.figgrp.3168 Figure 17-1.  The cell cycle] | [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mboc4.section.3738 Fertilization]
* '''Molecular Biology of the Cell''' 4th ed. Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter New York and London: Garland Science; c2002 - IV. Internal Organization of the Cell Chapter 17. The Cell Cycle and Programmed Cell Death [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mboc4.chapter.3167 Programmed Cell Death] |  [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mboc4.section.3169 An Overview of the Cell Cycle] | [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mboc4.figgrp.3168 Figure 17-1.  The cell cycle] | [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mboc4.section.3738 Fertilization]
* '''Molecular Cell Biology''' by Lodish, Harvey; Berk, Arnold; Zipursky, S. Lawrence; Matsudaira, Paul; Baltimore, David; Darnell, James E. New York: W. H. Freeman & Co.; c1999 Chapter 13. Regulation of the Eukaryotic Cell Cycle  [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mcb.chapter.3432 Regulation of the Eukaryotic Cell Cycle] | [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mcb.section.3463 Overview of the Cell Cycle and Its Control] | [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mcb.figgrp.3467 Figure 13-2.  Current model for regulation of the eukaryotic cell cycle]
* '''Molecular Cell Biology''' by Lodish, Harvey; Berk, Arnold; Zipursky, S. Lawrence; Matsudaira, Paul; Baltimore, David; Darnell, James E. New York: W. H. Freeman & Co.; c1999 Chapter 13. Regulation of the Eukaryotic Cell Cycle  [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mcb.chapter.3432 Regulation of the Eukaryotic Cell Cycle] | [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mcb.section.3463 Overview of the Cell Cycle and Its Control] | [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mcb.figgrp.3467 Figure 13-2.  Current model for regulation of the eukaryotic cell cycle] | '''Movies''' [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mcb.figgrp.5522 Proposed alternative mechanisms for chromosome congression.] | [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mcb.figgrp.5509 Centromeric attachment of microtubules.] | [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mcb.figgrp.5500 The stages of mitosis and cytokinesis in an animal cell.]
 
* '''The Cell - A Molecular Approach''' by Cooper, Geoffrey M. Sunderland (MA): Sinauer Associates, Inc.; c2000-  IV. Cell Regulation  Chapter 14. The Cell Cycle [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=cooper.section.2433 The Eukaryotic Cell Cycle] | [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=cooper.figgrp.2435 Figure 14.1.  Phases of the cell cycle] | [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=cooper.figgrp.2486 Figure 14.32. Comparison of meiosis and mitosis] | [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=cooper.figgrp.2492 Figure 14.37. Meiosis of vertebrate oocytes]
* '''The Cell - A Molecular Approach''' by Cooper, Geoffrey M. Sunderland (MA): Sinauer Associates, Inc.; c2000-  IV. Cell Regulation  Chapter 14. The Cell Cycle [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=cooper.section.2433 The Eukaryotic Cell Cycle] | [http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=cooper.figgrp.2435 Figure 14.1.  Phases of the cell cycle] | [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=cooper.figgrp.2486 Figure 14.32. Comparison of meiosis and mitosis] | [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=cooper.figgrp.2492 Figure 14.37. Meiosis of vertebrate oocytes]
* '''HSTAT''' - [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=hstat6.section.1395#1396 In Vitro Fertilization As A Medical Treatment For Male or Female Infertility]  
* '''HSTAT''' - [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=hstat6.section.1395#1396 In Vitro Fertilization As A Medical Treatment For Male or Female Infertility]
 
===Search ===
===Search ===


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* Salmon Lab [http://www.bio.unc.edu/faculty/salmon/lab/moviesmitosis.html Mitosis Movies]
* Salmon Lab [http://www.bio.unc.edu/faculty/salmon/lab/moviesmitosis.html Mitosis Movies]


== Next Lecture ==
{{2009ANAT2341}}
[[2009 Lecture 3|Lecture 3]] | [[2009 Lab 1|Lab 1]] |  [[ANAT2341_Embryology_2009#Course_Timetable|Course Timetable]]


:''Dr Mark Hill 2009'' UNSW CRICOS Provider Code No. 00098G
[[Category:Ovary]] [[Category:Ovulation]] [[Category:Fertilization]]
 
[[Category:2009ANAT2341]][[Category:Science-Undergraduate]]

Latest revision as of 10:10, 18 September 2014

Cell Division and Fertilization

This lecture will introduce two key concepts of biology, cell division and cellular sexual development. Both these concepts will also be explored further in the Thursday laboratory.

Textbooks

  • The Developing Human: Clinically Oriented Embryology (8th Edition) by Keith L. Moore and T.V.N Persaud - Chapter 2
  • Larsen’s Human Embryology - Chapter 1


Lectopia Lecture Audio Lecture Date: 28-07-2009 Lecture Time: 12:00 Venue: BioMed E Speaker: Mark Hill Cell Division and Fertilization

2010 Lecture - Cell Division and Fertilization

Cell Cycle

The Cell Cycle
  • Cell Division (m phase) is only a brief moment in the functional life (interphase) of most eukaryotic cells.
  • The eukaryotic cell cycle is regulated by 2 protein families known as cyclins and cyclin-dependent kinases.

Cell Division

Historic drawing of mitosis

Features Two Mechanical Processes

  • Mitosis - microtubule based segregation of chromosomes and formation of 2 nuclei
  • Cytokinesis - microfilament based splitting of the cell cytoplasmic contents as a whole into 2 daughter cells

Features Two Types

  • Mitosis - occurs in all cells, producing genetically identical progeny.
  • Meiosis - occurs only in germ cells (sperm=spermatozoa and egg=oocyte), producing genetically different progeny.
    • progeny = daughter cells, offspring

Cell Changes

  • Nucleus
    • Chromosome condensation
    • Nuclear envelope breakdown
  • Cytoplasm
    • Cytoskeleton reorganization
    • Spindle formation (MT) Contractile ring (MF)
    • Organelle redistribution

Mitosis

MCB Movie - The stages of mitosis and cytokinesis in an animal cell

  • Based on light microscopy of living cells light and electron microscopy of fixed and stained cells
  • 5 Phases - prophase, prometaphase, metaphase, anaphase, and telophase
  • Cytokinesis 6th stage overlaps the end of mitosis

Note that DNA duplication has occurred earlier in the S Phase of the cell cycle.


Prophase

  • Chromosome DNA has been earlier duplicated (S Phase)
  • Chromosomes begin condensing
  • Chromosome pairs (chromatids) held together at centromere
  • Microtubules disassemble
  • Mitotic spindle begins to form
  • Prophase ends when nuclear envelope breaks down

Prometaphase

MCB Movie - Centromeric attachment of microtubules |

  • Microtubules now enter nuclear region
  • Nuclear envelope forms vesicles around mitotic spindle
  • Kinetochores form on centromere attach to some MTs of spindle
  • Prometaphase ends when chromosomes move to metaphase plate

Metaphase

Metaphase fluorescent image of Mitotic spindle and Chromosomes
  • Kinetochore MTs align chromosomes in one midpoint plane
  • Metaphase ends when sister kinetochores separate

Anaphase

  • Separation of sister Kinetochores
  • shortening of Kinetochore microtubules pulls chromosome to spindle pole
  • Anaphase ends as nuclear envelope (membrane) begins to reform

Telophase

  • Chromosomes arrive at spindle poles
  • Kinetochore MTs lost
  • Condensed chromosomes begin expanding
    • Continues through cytokinesis

Cytokinesis

  • Division of cytoplasmic contents
  • Contractile ring forms at midpoint under membrane
  • Microfilament ring Contracts forming cleavage furrow
  • Eventually fully divides cytoplasm

Cell Organelles

  • Mitochondria - Divide independently of cell mitosis, distributed into daughter cells
  • Peroxisomes - localise at spindle poles
  • Endoplasmic Reticulum - associated with the nuclear envelope vesicles.
  • Golgi Apparatus- Golgi stack undergoes a continuous fragmentation process, fragments are distributed into daughter cells, then reassembled into new Golgi stacks

Meiosis

Meiosis Germ cell division (haploid)

  • Reductive division
  • Generates haploid gametes (egg, sperm)
  • Each genetically distinct from parent
  • Genetic recombination (prophase 1)
    • Exchanges portions of chromosomes maternal/paternal homologous pairs
  • Independent assortment of paternal chromosomes (meiosis 1)

Homologous chromosomes pairing unique to meiosis

  • Each chromosome duplicated and exists as attached sister chromatids before pairing occurs
  • Genetic Recombination shown by chromosomes part red and part black
    • chromosome pairing in meiosis involves crossing-over between homologous chromosomes

Meiosis I and II

  • Meiosis I separates the pairs of homologous chromosomes, reduces the cell from diploid to haploid.
  • Meiosis II separates each chromosome into two chromatids (chromosome behavior in meiosis II is like that of mitosis).

Figure 14.32. Comparison of meiosis and mitosis

Prophase I

  • The homologous chromosomes pair and exchange DNA to form recombinant chromosomes.
  • Prophase I is divided into five phases:
    • Leptotene - chromosomes start to condense.
    • Zygotene - homologous chromosomes become closely associated (synapsis) to form pairs of chromosomes consisting of four chromatids (tetrads).
    • Pachytene - crossing over between pairs of homologous chromosomes to form chiasmata (form between two nonsister chromatids at points where they have crossed over)
    • Diplotene - homologous chromosomes begin to separate but remain attached by chiasmata.
    • Diakinesis - homologous chromosomes continue to separate, and chiasmata move to the ends of the chromosomes.

Prometaphase I

  • Spindle apparatus formed, and chromosomes attached to spindle fibres by kinetochores.

Metaphase I

  • Homologous pairs of chromosomes (bivalents) arranged as a double row along the metaphase plate. The arrangement of the paired chromosomes with respect to the poles of the spindle apparatus is random along the metaphase plate. (This is a source of genetic variation through random assortment, as the paternal and maternal chromosomes in a homologous pair are similar but not identical. The number of possible arrangements is 2n, where n is the number of chromosomes in a haploid set. Human beings have 23 different chromosomes, so the number of possible combinations is 223, which is over 8 million.)

Anaphase I

The homologous chromosomes in each bivalent are separated and move to the opposite poles of the cell.

Telophase I

The chromosomes become diffuse and the nuclear membrane reforms.

Cytokinesis I

  • Cellular cytoplasmic division to form two new cells, followed by Meiosis II.

Prophase II

  • Chromosomes begin to condense, nuclear membrane breaks down and spindle forms.

Metaphase II

  • Spindle fibres attach to chromosomes, chromosomes align in cell centre.

Anaphase II

  • Chromosomes separate and move to the opposite poles of the cell.

Telophase II

  • Chromosomes reach spindle pole ends and the nuclear membrane reforms.

Cytokinesis

Cellular cytoplasmic division to form new cells.

Comparison of Meiosis/Mitosis

McGraw-Hill Animation comparing Mitosis and Meiosis

Comparison of Mitosis and Meiosis
  • After DNA replication 2 nuclear (and cell) divisions required to produce haploid gametes
  • Each diploid cell in meiosis produces 4 haploid cells (sperm) 1 haploid cell (egg)
  • Each diploid cell mitosis produces 2 diploid cells

Meiosis Differences

Female - Oogenesis

The Cell - Figure 14.37. Meiosis of vertebrate oocytes

  • Meiosis initiated once in a finite population of cells
  • 1 gamete produced / meiosis
  • Completion of meiosis delayed for months or years
  • Meiosis arrested at 1st meiotic prophase and reinitiated in a smaller population of cells
  • Differentiation of gamete occurs while diploid in first meiotic prophase
  • All chromosomes exhibit equivalent transcription and recombination during meiotic prophase

Male - Spermatogenesis

MBoC - Figure 20-27. The stages of spermatogenesis

  • Meiosis initiated continuously in a mitotically dividing stem cell population
  • 4 gametes produced / meiosis
  • Meiosis completed in days or weeks
  • Meiosis and differentiation proceed continuously without cell cycle arrest
  • Differentiation of gamete occurs while haploid after meiosis ends
  • Sex chromosomes excluded from recombination and transcription during first meiotic prophase

Polar Bodies

Early zygote showing polar bodies
  • In female gametogenesis only a single (1) haploid egg is produced from meiosis. In male gametogenesis four (4) haploid sperm are produced from meiosis. So what happens to all the extra DNA in producing this single egg?
    • In Meiosis 1 the "extra" DNA is excluded to the periphery as a 1st polar body, which encloses the extra DNA.
    • In Meiosis 2 the "extra" DNA is once again excluded as a 2nd polar body. The first polar body may also under go meiosis 2 producing a 3rd polar body.
  • These polar bodies are not gametes.
  • Polar bodies appear to have no other function other than to dispose of the extra DNA in oogenesis.
    • Recent research in mice suggest that the position of oocyte polar body may influence fertilization site.

Abnormalities

Trisomy21arrow.gifTrisomy21female.jpgTrisomy21male.jpg

  • The most common chromosome abnormality is aneuploidy, the gain or loss of whole chromosomes.
  • Caused by meiotic nondisjunction, the failure of chromosomes to correctly separate homologues during meiosis I or sister chromatids during meiosis II.
  • Down Syndrome - caused by an extra copy of chromosome 21. Abnormal Development - Trisomy 21 (Down Syndrome)
  • Chromosomal translocations occur when there is an inappropriate exchange of chromosomal material. Philadelphia chromosome
  • Philadelphia chromosome - piece of Chr9 exchanged with Chr22 Generates truncated abl, overstimulates cell production, leads to chronic myelogenous leukemia

Fertilization

MH - Gamete formation, menstrual cycle and fertilization will also be covered in this week's Laboratory. We may not complete all content shown below within the lecture.

Fertilization is the complete process resulting in the fusion of haploid gametes, egg and sperm, to form the diploid zygote. The recent development of aided fertilization is described as in vitro fertilization (in vitro = "in glass", outside the body, IVF). Clinically, all these aided fertilization techniques are grouped as Assisted Reproductive Technologies or ART.

UNSW Embryology Links: Week 1 - Spermatogenesis | Week 1 - Oogenesis | Week 1 - Fertilization | In Vivo Fertilization | In Vitro Fertilization


Fertilization Preparation

Prior to the fertilization process commencing both the gametes oocyte (egg) and spermatozoa (sperm) require completion of a number of biological processes.

  • Oocyte Meiosis - completes Meiosis 1 and commences Meiosis 2 (arrests at Metaphase II).
  • Spermatozoa Capacitation - following release (ejaculation) and mixing with other glandular secretions, activates motility and acrosome preparation.
  • Migration - both Oocyte and Spermatozoa.
    • oocyte ovulation and release with associated cells, from ovary into fimbria then into uterine tube (oviduct, uterine horn, fallopian tube) and epithelial cilia mediated movement.
    • spermatozoa ejaculation, deposited in vagina, movement of tail to "swim" in uterine secretions through cervix, uterine body and into uterine tube, have approximately 24-48h to fertilize oocyte.

Endocrinology - Diagram of the comparative anatomy of the male and female reproductive tracts

Oogenesis

Week 1 - Oogenesis

Histology of the Ovary
Preantral Follicle
Antral Follicle and Oocyte
  • Process of oogonia mature into oocytes (ova, ovum, egg)
  • all oogonia form primary oocytes before birth, therefore a maturation of preexisting cells in the female gonad, ovary

Oocytenumber.jpg

  • humans usually only 1 ovum released every menstrual cycle (IVF- superovulation)
  • oocyte and its surrounding cells = follicle
  • primary -> secondary -> ovulation releases

Ovary- Histology - whole transverse section (cortex, medulla)

Menstrual Cycle

  • Primary Oocyte - arrested at early Meiosis 1
    • diploid: 22 chromosome pairs + 1 pair X chromosomes (46, XX)
    • autosomes and sex chromosome
  • Oogenesis- pre-antral then antral follicle (Graafian follicle is mature antral follicle released)
  • Secondary oocyte
    • 1 Day before ovulation completes (stim by LH) Meiosis 1
    • haploid: 22 chromosomes + 1 X chromosome (23, X)
    • nondisjunction- abnormal chromosome segregation
    • begins Meiosis 2 and arrests at metaphase
    • note no interphase replication of DNA, only fertilization will complete Meiosis 2

Ovulation (HPG Axis)

HPG Axis

  • Hypothalmus releases gonadotropin releasing hormone (GRH, luteinizing hormone–releasing hormone, LHRH) -> Pituitary releases follicle stimulating hormone (FSH) and lutenizing hormone (LH) -> ovary follicle development and ovulation.
    • release of the secondary oocyte and formation of corpus luteum
    • secondary oocyte encased in zona pellucida and corona radiata
  • Ovulation associated with follicle rupture and ampulla movement.

Zona Pellucida

MBoC - Figure 20-21. The zona pellucida

  • glycoprotein shell ZP1, ZP2, ZP3
  • mechanical protection of egg
  • involved in the fertilization process
  • sperm binding
  • adhesion of sperm to egg
  • acrosome reaction
    • releases enzymes to locally breakdown
  • block of polyspermy
    • altered to prevent more than 1 sperm penetrating
    • may also have a role in development of the blastocyst

Corona Radiata

  • granulosa cells and extracellular matrix
  • protective and nutritional role for cells during transport
  • cells are also lost during transport along oviduct

Gamete formation- Spermatogenesis

Week 1 - Spermatogenesis

  • process of spermatagonia mature into spermatazoa (sperm)
  • continuously throughout life occurs in the seminiferous tubules in the male gonad- testis (plural testes)
  • at puberty spermatagonia activate and proliferate (mitosis)
  • primary spermatocyte -> secondary spermatocyte-> spermatid->sperm
  • Seminiferous Tubule is site of maturation involving meiosis and spermiogenesis
  • Spermatogenesis- Meiosis
  • meiosis is reductive cell division
    • 1 spermatagonia (diploid) 46, XY (also written 44+XY) = 4 sperm (haploid); 23, X 23, X 23, Y 23, Y

Spermiogenesis

  • morphological (shape) change from round spermatids to elongated sperm
  • loose cytoplasm
  • Transform golgi apparatus into acrosome (in head)
  • Organize microtubules for motility (in tail, flagellum)
  • Segregate mitochondria for energy (in tail)

Ejaculate

  • By volume <10 % sperm and accessory glands contribute majority of volume (60 % seminal vesicle, 10 % bulbourethral, 30 % prostate)
  • 3.5 ml, 200-600 million sperm
  • Capacitation is the removal of glycoprotein coat and seminal proteins and alteration of sperm mitochondria
  • Infertility can be due to Oligospermia, Azoospermia, Immotile Cilia Syndrome
    • Oligospermia (Low Sperm Count) - less than 20 million sperm after 72 hour abstinence from sex
    • Azoospermia (Absent Sperm) - blockage of duct network
    • Immotile Cilia Syndrome - lack of sperm motility

Fertilization Site

  • Fertilization usually occurs in first 1/3 of oviduct
  • Fertilization can also occur outside oviduct, associated with In Vitro Fertilization (IVF, GIFT, ZIFT...) and ectopic pregnancy
  • The majority of fertilized eggs do not go on to form an embryo

Fertilization - Spermatozoa

Fertilization- Oocyte

Formation of the Zygote

Early human zygote showing Pronuclei
  • Pronuclei - Male and Female haploid nuclei approach each other and nuclear membranes break down
  • chromosomal pairing, DNA replicates, first mitotic division
  • Sperm contributes - centriole which organizes mitotic spindle
  • Oocyte contributes - mitochondria (maternally inherited)

Sex Determination

  • based upon whether an X or Y carrying sperm has fertilized the egg, should be 1.0 sex ratio.
  • actually 1.05, 105 males for every 100 females, some studies show more males 2+ days after ovulation.
  • cell totipotent (equivalent to a stem cell, can form any tissue of the body)

Men - Y Chromosome

  • Y Chromosome carries Sry gene, protein product activates pathway for male gonad (covered in genital development)

Women - X Chromosome

  • Gene dosage, one X chromosome in each female embryo cell has to be inactivated
  • process is apparently random and therefore 50% of cells have father's X, 50% have mother's X
  • Note that because men only have 1 X chromosome, if abnormal, this leads to X-linked diseases more common in male that female where bothe X's need to be abnormal.

UNSW Embryology Links

References

Textbooks

  • The Developing Human: Clinically Oriented Embryology (8th Edition) by Keith L. Moore and T.V.N Persaud - Chapter 2
  • Larsen’s Human Embryology by GC. Schoenwolf, SB. Bleyl, PR. Brauer and PH. Francis-West - Chapter 1

Online Textbooks

Search

Reviews

  • Cell cycle studies based upon quantitative image analysis. Stacey DW, Hitomi M. Cytometry A. 2008 Apr;73(4):270-8. Review. PMID: 18163464
  • Analysis of cell cycle phases and progression in cultured mammalian cells. Schorl C, Sedivy JM. Methods. 2007 Feb;41(2):143-50. Review. PMID: 17189856

Articles

External Links

Glossary Links

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Course Content 2009

Embryology Introduction | Cell Division/Fertilization | Cell Division/Fertilization | Week 1&2 Development | Week 3 Development | Lab 2 | Mesoderm Development | Ectoderm, Early Neural, Neural Crest | Lab 3 | Early Vascular Development | Placenta | Lab 4 | Endoderm, Early Gastrointestinal | Respiratory Development | Lab 5 | Head Development | Neural Crest Development | Lab 6 | Musculoskeletal Development | Limb Development | Lab 7 | Kidney | Genital | Lab 8 | Sensory - Ear | Integumentary | Lab 9 | Sensory - Eye | Endocrine | Lab 10 | Late Vascular Development | Fetal | Lab 11 | Birth, Postnatal | Revision | Lab 12 | Lecture Audio | Course Timetable


Cite this page: Hill, M.A. (2024, March 28) Embryology 2009 Lecture 2. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2009_Lecture_2

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G