Carnegie stage 2

Embryology - 1 Dec 2023 Expand to Translate
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Introduction

First cell mitotic divisions of the zygote forming initially 2 blastomeres that continue to divide to form the morula, a "berry", a solid mass of cells.

This early mitosis is a unique embryonic cell cycle (M, S, M phases) compared to adult (M, G₁, S, G₂, M phase). With virtually no G₁ or G₂ phases this results in a reduction in cytoplasmic volume of each daughter cell with each cell division.

Summary

Week 1, 2 - 3 days, size 0.1 - 0.2 mm
Morula, zona pellucida, blastomeres

Carnegie Collection

Two cell blastomere (1-2 days)

Carnegie Collection - Stage 2
Serial No.	Normality	No. of Blastomeres	Size of Fixed Specimen (µm)	Fixative	Embedding Medium	Thinness (µm)	Stain	Year	Notes
8190	abnormal	9	160x104	Alc. & Bouin	C-P	6	Iron h., or G	1943	Hertig et al. (1954)
8260	in vitro	2	50x75	Bouin	C-P	8	(Stain - Haematoxylin Eosin)	1944	Menkin and Rock (1948)
8450	abnormal	8	100x96	Alc. & Bouin	C-P	6	(Stain - Haematoxylin Eosin), phlox.	1947	Hertig et al. (1954)
8452	abnormal	12	110x93	Alc. & Bouin	C-P	6	(Stain - Haematoxylin Eosin), phlox.	1946	Hertig et al. (1954)
8500.1	in vitro	3	50x86	Bouin	C-P	8	(Stain - Haematoxylin Eosin)	1947	Menkin and Rock (1948)
8630	abnormal	5	104x94	Alc. & Bouin	C-P	6	(Stain - Haematoxylin Eosin)	1948	Hertig et al. (1954)
8698	normal	2	122x88	Alc. & Bouin	C-P	6	(Stain - Haematoxylin Eosin)	1949	Hertig et al. (1954)
8904	normal	12	115		Specimen lost			1951	Hertig et al. (1954)
Abbreviations Embedding medium - paraffin (P) or a combination of celloidin and paraffin (C-P). Fixative - formalin (Formol), alcohol and formalin (Alc, formol), Bouin (Bouin solution) ? - unknown or not determined.
Hertig AT. Rock J. Adams EC. and Mulligan W.J. On the preimplantation stages of the human ovum: a description of four normal and four abnormal specimens ranging from the second to the fifth day of development. (1954) Carnegie Instn. Wash. Publ. 603, Contrib. Embryol., 35: 199-220. Menkin MR. and Rock J. In vitro fertilization and cleavage of human ovarian eggs. (1948) Amer. J. Obstet. Gynecol, 55, 440-452. PMID 18903892

Events

mitosis

Some Recent Findings

mouse - Asymmetric expression of maternal mRNA governs first cell-fate decision^[1] "The goal of preimplantation development is to establish the fates of the embryonic and extra-embryonic cells. However, when and how cell fates are determined during early mammalian embryonic development remains unclear. We report that the high mobility group (HMG) protein family member HMGA1 was distributed differentially in mouse two-cell blastomeres. Knockdown of Hmga1 expression in one of the two cells reduced the number of cells contributing to the inner cell mass (ICM), suggesting that differential distribution of HMGA1 in the blastomeres in two-cell mouse embryos affected the selection of embryonic cell lineages. Mechanistically, HMGA1 promotes the expression of the ICM-specific gene Sox2. The results of this study show that mouse embryos demonstrate heterogeneity as early as the two-cell stage, and that these differences are related to cell-fate differentiation in early mouse embryos."

References

↑ Wang Y, Zheng X, Cheng R, Han J, Ma X, Xu W, Gao L, Lei A, Liu J, Quan F, Zhang Y & Liu X. (2021). Asymmetric expression of maternal mRNA governs first cell-fate decision. FASEB J , 35, e22006. PMID: 34694646 DOI.

Hertig AT. Rock J. and Adams EC. A description of 34 human ova within the first 17 days of development. (1956) Amer. J Anat., 98:435-493.

References

Hertig AT. Rock J. and Adams EC. A description of 34 human ova within the first 17 days of development. (1956) Amer. J Anat., 98:435-493.

Additional Images

Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline

Cite this page: Hill, M.A. (2023, December 1) Embryology Carnegie stage 2. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_2

What Links Here?

[PMID34694646-1] Wang Y, Zheng X, Cheng R, Han J, Ma X, Xu W, Gao L, Lei A, Liu J, Quan F, Zhang Y & Liu X. (2021). Asymmetric expression of maternal mRNA governs first cell-fate decision. FASEB J , 35, e22006. PMID: 34694646 DOI.

[1]

Week:	1	2	3	4	5	6	7	8
Carnegie stage:	1 2 3 4	5 6	7 8 9	10 11 12 13	14 15	16 17	18 19	20 21 22 23


Two-cell segmenting egg	Mid-serial section two-cell

Human Embryo (day 2)	Human Embryo (day 3)