UNSW Embryology

Beginnings, Growth and Development

© Dr Mark Hill (2008)

Acknowledgements

Laboratory 3 - Early Cell Division

The images below show the early development of the 1-chambered conceptus (blastocyst).

From Oocyte to Blastocyst.

(a,b,e,f- human) (c- mouse) (d- worm)

(a) Mature oocyte with zona pellucida and surrounded by follicular cells (corona radiata). These cells provide oocyte protection, are the first barrier to sperm, and following are shed fertilization.

(b) Zygote showing 2 polar bodies and male and female pronuclei prior to their fusion. Note that corona radiata has been lost,but that zona pellucia is still present.

(c) Mixing of 2 parental genomes contained within each pronuclei during initial divisions of the zygote. Oocyte genome labelled blue, sperm genome labelled green (Note Movie requires Quicktime to be installed on your computer)

(d) Early cell division (4-cell stage) of zygote, continued divison to 16 cell stage forms the morula stage (solid ball of cells).

(e) Movie ( Warning- Large file 3.2 Mb click image to play) showing cell division from 2 blastomeres (showing mitotic spindle) to late morula stage. Note the cell division occurs within the zona pellucida with a sequential reduction in cytoplasmic volume. Nuclei are shown by coloured ring overlays. (Note Movie requires Quicktime to be installed on your computer)

(f) Blastocyst stage with flattened outer shell of trophoblasts and inner cell mass (visible as a dark spot). Inner cell mass will give rise to the bilaminar then the trilaminar embryonic disc.

Online Textbooks

MBoC - Mouse Blastocyst Development

Next

Link to next page in this Practical 3 - Implantation, Week 2

Glossary

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

Terms

• bilaminar- having 2 layers
• blastocyst- the developmental stage following morula, as this stage matures, the zona pellucia is lost allowing the conceptus to adplant and then implant into the uterine wall.
• blastomeres-the cells resulting from the initial rounds of mitotic division of the zygote. These cells become smaller (in cytoplasmic volume) with each division.
• corona radiata- Layer of follicle cells of cumulus oophorus remaining attached to zona pellucida of oocyte after ovulation.
• inner cell mass- the clump of cells found inside the blastocyst. These cells will go in to form the embryo, these are the "stem cells" (we here about in the media) that are totipotential, they can form any tissue in the embryo. Mature oocyte-the female germ cell released at ovulation from the ovary.
• morula &endash;(L. morus = mulberry) early stage of development (12-15 cells) Followed by formation of a cavity in the mass (blastocyst stage). (More? Week 1 Notes)
• parental genomes- the male (sperm) and female (oocyte) DNA which contributes to the embryo's cells.
• polar bodies- 3 exclusion bodies which contain the DNA not used by the embryo. Contributed to initially by the meiotic division of the oocyte.
• pronuclei- the male (sperm) and female (oocyte) nuclei within the fertilized oocyte, prior to their combination to form the new embryo's nuclei.
• trilaminar embryonic disc- the 3 layered embryo stage.
• Trophoblasts- (Gr. trophe = nutrition) outer layer of cells on blastocyst that will generate the embryonic part of the placenta.
• zona pellucida- glycoprotein shell that surrounds the oocyte through to blastula stage of development.
• Zygote- The first cell stage following fertilization of the oocyte by the sperm. This is the first cell of the conceptus which will divide into blastomeres.

Online Resources

UNSW Embryology

Human Menstrual Cycle

Week 1 Development

Week 2 Development

Quick Links

UNSW Embryology ISBN: 978 0 7334 2609 4

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