Carnegie stage 2

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Introduction

Stage2.jpg 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


See also Events

Stage 2 Links: Week 1 | Morula | Blastocyst | Mitosis | Zona pellucida | Lecture | Medicine Practical | Science Practical | Next Stage 3
  Historic Papers: 1956
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
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


Hertig1956 fig01.jpg Hertig1956 fig02.jpg
Two-cell segmenting egg Mid-serial section two-cell
Stage 2 Day 2 Stage 2 Day 3
Human Embryo (day 2) Human Embryo (day 3)

See also Human oocyte to blastocyst

Carnegie Collection

Stage2 bf01.jpg

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.

Events


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

  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.

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. (2024, April 22) Embryology Carnegie stage 2. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_2

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