UNSW Embryology

Week 1

© Dr Mark Hill (2008)

Acknowledgements

Introduction

The first week of human development begins with fertilization of the egg by sperm forming the zygote, followed by early cell division forming the blastocyst. These notes also cover events before fertilization formation of both the egg and sperm, gametogenesis. Cell division can occur in 2 forms, mitosis and meiosis. Mitosis can occur in all cells, while meiosis only occurs during the formation of the sex gametes.

Initially, there is a halving of choromosomal content in the gametes, which is restored by fertilization, allowing genetic recombination to occur. This is then followed by a series of cell divisions without cytoplasmic growth.

I have also included in the Week 1 notes information about male sex determination and X inactivation, which are not really specific to the first week of development.

Zygote with 2 pronuclei
Dr S. J. DiMarzo

Some Recent Findings

Akiyama T, Nagata M, Aoki F. Inadequate histone deacetylation during oocyte meiosis causes aneuploidy and embryo death in mice. Proc Natl Acad Sci U S A. 2006 May 1; [Epub ahead of print] "It was recently reported that histones are globally deacetylated in mammalian oocytes during meiosis but not mitosis. ... The high incidence of aneuploidy in the embryos of older females may be due to inadequate meiotic histone deacetylation."

Wang Q, Yin S, Ai JS, Liang CG, Hou Y, Chen DY, Schatten H, Sun QY. Histone deacetylation is required for orderly meiosis. Cell Cycle. 2006 Apr;5(7):766-74. Epub 2006 Apr 1. The results showed that subcellular translocation, expression level and phosphorylated modification of histone deacetylase 1 were temporally regulated and likely to coparticipate in the establishment of histone acetylation profiles in oocyte meiosis."

Meiosis Overview

The following is a brief text extract from a lecture on Cell Division. As it is only the text bullet points covering meiosis, out of context it may be hard to follow. There are several full versions of this lecture available online from UNSW Cell Biology website: Medicine- Society and Health , Science- Cell Biology

Text References

Available Online

• Molecular Biology of the Cell (Alberts) Ch17,18
• The Cell Ch14,15
• Molecular Cell Biology Ch13

Not Available Online

• Essential Cell Biology (Alberts) Ch 17
• Histology and Cell Biology (Kierszbaum) All throughout textbook Textbooks
• Dev Biology: Ch12

Cell Birth - Mitosis and Meiosis

1st cell division- Meiosis
• 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
• For clarity only 1 pair of homologous chromosomes shown
• Text modified from MBoC

  Comparison of Meiosis/Mitosis

• After DNA replication
• 2 nuclear (and cell) divisions required to produce haploid gametes
• Each diploid cell in meiosis produces 4 haploid cells
• Each diploid cell mitosis produces 2 diploid cells
• only one pair of homologous chromosomes is shown
• Text modified from MBoC

  Meiotic Nondisjunction

• Occurs when homologues fail to separate
• during meiotic division I or II
• Down Syndrome
• Caused by an extra copy of chromosome 21

  Genome Modifications

• chromosomal translocations
• Philadelphia chromosome
• Chronic myelogenous leukemia
• Piece of Chr9 exchanged with Chr22
• Generates truncated abl
• Overstimulates cell production

  Differences in Mammalian Meioses

  Female oogenesis

• 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

• 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

References

Molecular Biology of the Cell- References

Go to this page and clicking on author's name will open abstract or use link to similar articles from PubMed.

• meiosis

26 citations found

Zhan XL, et al.           [See Related Articles]

Essential functions of protein tyrosine phosphatases ptp2 and ptp3 and rim11 tyrosine phosphorylation in saccharomyces cerevisiae meiosis and sporulation.
Mol Biol Cell. 2000 Feb;11(2):663-76.
[MEDLINE record in process]
PMID: 10679022; UI: 20143586.

Hicks JL, et al.           [See Related Articles]

Class VI unconventional myosin is required for spermatogenesis in Drosophila.
Mol Biol Cell. 1999 Dec;10(12):4341-53.
PMID: 10588662; UI: 20056109.

Sohaskey ML, et al.           [See Related Articles]

Distinct, constitutively active MAPK phosphatases function in Xenopus oocytes: implications for p42 MAPK regulation In vivo.
Mol Biol Cell. 1999 Nov;10(11):3729-43.
PMID: 10564268; UI: 20032171.

Grether ME, et al.           [See Related Articles]

Genetic and biochemical characterization of the yeast spo12 protein.
Mol Biol Cell. 1999 Nov;10(11):3689-703.
PMID: 10564265; UI: 20032168.

Culp PA, et al.           [See Related Articles]

c-mos and cdc2 cooperate in the translational activation of fibroblast growth factor receptor-1 during Xenopus oocyte maturation.
Mol Biol Cell. 1999 Nov;10(11):3567-81.
PMID: 10564256; UI: 20032159.

Gavin AC, et al.           [See Related Articles]

A p90(rsk) mutant constitutively interacting with MAP kinase uncouples MAP kinase from p34(cdc2)/cyclin B activation in Xenopus oocytes.
Mol Biol Cell. 1999 Sep;10(9):2971-86.
PMID: 10473640; UI: 99402804.

Fowler TJ, et al.           [See Related Articles]

Multiple sex pheromones and receptors of a mushroom-producing fungus elicit mating in yeast.
Mol Biol Cell. 1999 Aug;10(8):2559-72.
PMID: 10436012; UI: 99365150.

Alsheimer M, et al.           [See Related Articles]

Architecture of the nuclear periphery of rat pachytene spermatocytes: distribution of nuclear envelope proteins in relation to synaptonemal complex attachment sites.
Mol Biol Cell. 1999 Apr;10(4):1235-45.
PMID: 10198069; UI: 99214008.

Hartsuiker E, et al.           [See Related Articles]

The role of topoisomerase II in meiotic chromosome condensation and segregation in Schizosaccharomyces pombe.
Mol Biol Cell. 1998 Oct;9(10):2739-50.
PMID: 9763441; UI: 98437181.

Simerly C, et al.           [See Related Articles]

Differential expression and functions of cortical myosin IIA and IIB isotypes during meiotic maturation, fertilization, and mitosis in mouse oocytes and embryos.
Mol Biol Cell. 1998 Sep;9(9):2509-25.
PMID: 9725909; UI: 98395051.

Rudge SA, et al.           [See Related Articles]

ADP-Ribosylation factors do not activate yeast phospholipase Ds but are required for sporulation.
Mol Biol Cell. 1998 Aug;9(8):2025-36.
PMID: 9693364; UI: 98359829.

Högstrand K, et al.           [See Related Articles]

Gene Conversion of Major Histocompatibility Complex Genes in the Mouse Spermatogenesis is a Premeiotic Event.
Mol Biol Cell. 1997 Dec 1;8(12):2511-7.
[Record as supplied by publisher]
PMID: 9398672.

Marko JF, et al.           [See Related Articles]

Polymer models of meiotic and mitotic chromosomes.
Mol Biol Cell. 1997 Nov;8(11):2217-31.
PMID: 9362064; UI: 98028157.

Tarsounas M, et al.           [See Related Articles]

Protein-protein interactions in the synaptonemal complex.
Mol Biol Cell. 1997 Aug;8(8):1405-14.
PMID: 9285814; UI: 97431777.

Elfring LK, et al.           [See Related Articles]

Drosophila PLUTONIUM protein is a specialized cell cycle regulator required at the onset of embryogenesis.
Mol Biol Cell. 1997 Apr;8(4):583-93.
PMID: 9247640; UI: 97390805.

Ochs RL, et al.           [See Related Articles]

cDNA cloning and characterization of a novel nucleolar protein.
Mol Biol Cell. 1996 Jul;7(7):1015-24.
PMID: 8862517; UI: 97015880.

Sperry AO, et al.           [See Related Articles]

Kinesin-related proteins in the mammalian testes: candidate motors for meiosis and morphogenesis.
Mol Biol Cell. 1996 Feb;7(2):289-305.
PMID: 8688559; UI: 96228687.

Smith MG, et al.           [See Related Articles]

Organelle-cytoskeletal interactions: actin mutations inhibit meiosis-dependent mitochondrial rearrangement in the budding yeast Saccharomyces cerevisiae.
Mol Biol Cell. 1995 Oct;6(10):1381-96.
PMID: 8573793; UI: 96117051.

Li J, et al.           [See Related Articles]

Requirement for phosphorylation of cyclin B1 for Xenopus oocyte maturation.
Mol Biol Cell. 1995 Sep;6(9):1111-24.
PMID: 8534910; UI: 96079260.

Richler C, et al.           [See Related Articles]

Splicing components are excluded from the transcriptionally inactive XY body in male meiotic nuclei.
Mol Biol Cell. 1994 Dec;5(12):1341-52.
PMID: 7696714; UI: 95210752.

Taagepera S, et al.           [See Related Articles]

The MPM-2 antibody inhibits mitogen-activated protein kinase activity by binding to an epitope containing phosphothreonine-183.
Mol Biol Cell. 1994 Nov;5(11):1243-51.
PMID: 7532473; UI: 95170120.

Brown AJ, et al.           [See Related Articles]

Expression and activity of p40MO15, the catalytic subunit of cdk-activating kinase, during Xenopus oogenesis and embryogenesis.
Mol Biol Cell. 1994 Aug;5(8):921-32.
PMID: 7803859; UI: 95102156.

Pickham KM, et al.           [See Related Articles]

Mutants at Ser277 of Xenopus cdc2 protein kinase induce oocyte maturation in the absence of the positive regulatory phosphorylation site Thr161.
Mol Biol Cell. 1994 May;5(5):587-96.
PMID: 7919539; UI: 95003216.

Galas S, et al.           [See Related Articles]

A nuclear factor required for specific translation of cyclin B may control the timing of first meiotic cleavage in starfish oocytes.
Mol Biol Cell. 1993 Dec;4(12):1295-306.
PMID: 7513215; UI: 94220786.

Stith BJ, et al.           [See Related Articles]

Inositol 1,4,5-trisphosphate mass changes from fertilization through first cleavage in Xenopus laevis.
Mol Biol Cell. 1993 Apr;4(4):435-43.
PMID: 8507898; UI: 93283738.

Lee MS, et al.           [See Related Articles]

cdc25+ encodes a protein phosphatase that dephosphorylates p34cdc2.
Mol Biol Cell. 1992 Jan;3(1):73-84.
PMID: 1312880; UI: 92199341.

Quick Links

Week 1 Pages:

Introduction | Abnormalities | Gamete formation | Cell division | Fertilization | Zygote | Blastocyst | Male sex determination| X inactivation | References | Text only page | WWW Links |

Development Notes ----------------- Menstrual Cycle Week 1 Week 2 Week 3 Week 4 Placenta Serial Images Genes/DNA Molecular Dev Abnormal Dev Postnatal Dev Notes Index

System Notes ----------------- Heart/Cardiovascular Respiratory Coelomic cavity Gastrointestinal Tract Head and Neck Neural Neural Crest Eye Ear Nose Endocrine Urogenital Musculoskeletal Integumentary

Movies ----------------- Embryo Growth Ultrasound Week 1 Week 2 Week 3 Week 4 Stage 13/14 Stage 22 Neural Head and Neck Heart Vasculature Gastrointestinal Urogenital Other Embryos Larsen Internet

Other Embryos ----------------- Chicken Fly Frog Mouse Rabbit Rat Worm Zebrafish Guinea Pig

UNSW Embryology ISBN: 978 0 7334 2609 4

UNSW CRICOS Provider Code No. 00098G