2009 Group Project 4

MOUSE

Staging

Mouse embryonic development commences once the female's egg or oocyte has become fertilized by the male's sperm. Mouse development has a gestation period of 19-21 days, and can range in different strains of mice. The development of an embryo can be categorized into different stages including cell number, somite stages and morphology. The most common method of staging is by Theiler (1989) which categorizes mouse development into prenatal and postnatal stages consisting of 26 and 2 stages respectively.

Table 1: Mouse embryonic stages of development from fertilization to zona free blastocyst (Stages 1 to 5)

Theiler Stage	Embryonic Age in Days Post Coitum (dpc)	Stage Characteristic	Cell Characteristics	Zona Pellucida	Location
1	0-0.9 (range 0-0.25)	One-celled embryo (fertilized)	One cell	Present	Ampulla
2	1 (range 1-2.5)	Dividing egg	2-4 cells - 1st cleavage after 24hrs	Present	Travelling down oviduct
3	2 (range 1-3.5)	Morula (early to fully compacted)	4-16 cells	Present	Oviduct. Usually near utero-tubal junction.
4	3 (range 2-4)	Change from Morula to Blastocyst -Intra-cellular matrix present -Blastocoelic cavity evident	16-40 compacted cells -Inner cell mass -Outer layer of trophectoderm cells	Present	Uterine lumen
5	4 (range 3-5.5)	Zona free Blastocyst (hatching)	Blastocyst is ready to implant as surrounding cell layer of zona pelludica is lost	Absent	Uterine lumen

Dr Mark Hill 2009, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G

Figure 1: Illustration of Mouse embryonic stages of development from fertilization to zona free blastocyst (stages 1 to 5). E.Newton 2009

Once the mouse blastocyst has implanted on the uterine wall, the embryo undergoes many changes in size and shape to form a cylindrical structure. Cell proliferation of embryonic ectoderm is activated and results in an increase in embryonic tissue volume. Along with this growth, is the growth of the inner cell mass and trophectoderm layer. The inner cell mass and trophectodermal cells proliferate into the space made by the blastocoel cavity to form a layer of epiblast cells and the pro-amniotic cavity. This results in two layers;

• the inner epiblast layer
• the outer visceral endoderm layer.

This stage or egg cylinder stage is evident of the well defined extra-embryonic and embryonic regions. The embryo can now be visualized with a dorsal and ventral surface. These two surfaces consist of the pro-amniotic cavity surface of epiblast cells on the dorsal surface and the outer layer of visceral endoderm cells on the ventral surface.

References

1. Dr Mark Hill 2009, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G [1]

2. Bard, Kaufman, Dubreuil, Brune, Burger, Baldock, Davidson (1998). An internet accessible database of mouse development anatomy based on a systemic nomenclature, Mechanisms of development, (74) 111-120.

ANAT2341 group projects

Project 1 - Rabbit | Project 2 - Fly | Project 3 - Zebrafish | Group Project 4 - Mouse | Project 5 - Frog | Students Page | Animal Development