UNSW Embryology

Week 1

© Dr Mark Hill (2008)

Acknowledgements

Introduction

Cleavage of the Zygote forms 2 blastomeres, cleavage with no cytoplasm synthesis, therefore individual cell volume decreases (More? embryonic cell cycle).

2 Blastomeres
(More? see quicktime movie of early cell division)

The zygote divides and develops into a solid ball of cells, the morulla, so called because of its mulberry-like appearance.

Cell division is initially synchronous, then asynchronous (slow- centre cells, larger fast- peripheral cells, flattened against zona pellucida). The solid ball of cells undergoes compaction (day 3-4) and then a cavity begins to form inside the ball, this whole structure becomes the blastocyst (day 5).

The blastocyst has 2 cell populations: an inner cell mass (which will form the entire embryo) and a shell of cells (cytotrophoblastic shell, which will form the placenta). From the blastocyst stage onward different populations of cells begin to be established.

Human embryo- in vitro blastocyst formation

Timecourse: Fertilization, Day 2-5 cell division, Day 5 cell compaction, early and late cavitation, early blastocyst, expanding blastocyst.

(Modified from Fong and Bongso, Human Reproduction 1999 | see also images of in vitro blastocyst formation)

Some Recent Findings

Recent review by Chen HW, Chen JJ, Yu SL, Li HN, Yang PC, Su CM, Au HK, Chang CW, Chien LW, Chen CS, Tzeng CR. Transcriptome analysis in blastocyst hatching by cDNA microarray. Hum Reprod. 2005 Sep;20(9):2492-501.

A microarray study of hatching specific genes in the mouse blastocyst showing high expression of adhesion and migration molecues required for blastocyst attachment and altered levels in delayed growth embryos. They also demonstrated corresponding strong and specific immunostaining of E-cadherin and NCAM in hatched blastocysts.

Hatching specific genes include:

• cell adhesion and migration molecules - E-cadherin, neuronal cell adhesion molecule (NCAM), lectin, galactose binding, soluble 7 (Lgals7), vanin 3, biglycan
• epigenetic regulators - Dnmt1, SIN3 yeast homolog A
• stress response regulators - Dnmt1, SIN3 yeast homolog A
• immunoresponse regulators - interleukin (IL)-2-inducible T-cell kinase, IL-4R, interferon- receptor 2, neurotrophin

Embryonic Cell Cycle

These early embryonic cell cycles differ by having little or no intervening growth phases simply Mitosis and DNA replication.

Embryonic cell cycle: Cell Division (Mitosis, M Phase) - DNA synthesis (S Phase) Cell Division (Mitosis, M Phase) - DNA synthesis (S Phase)

Normal cell cycle: Cell Division (Mitosis, M Phase) - Growth Phase 1 (G1 Phase) - DNA synthesis (S Phase) Growth Phase 2 (G2 Phase) - (Mitosis, M Phase)

(More? Mitosis)

References

Links: Journals | Online Textbooks | Search Textbooks | PubMed | Search PubMed | Glossary

PubMed

Reviews

Lynn Lamoreux M, Kelsh RN, Wakamatsu Y, Ozato K. Pigment pattern formation in the medaka embryo. Pigment Cell Res. 2005 Apr;18(2):64-73.

Articles

Chen HW, Chen JJ, Yu SL, Li HN, Yang PC, Su CM, Au HK, Chang CW, Chien LW, Chen CS, Tzeng CR. Transcriptome analysis in blastocyst hatching by cDNA microarray. Hum Reprod. 2005 Sep;20(9):2492-501.

Old References from 1999:

• Expression of Fgfr2 in the early mouse embryo indicates its involvement in preimplantation development. Haffner-Krausz R, Gorivodsky M, Chen Y, Lonai P Mech Dev 1999 Jul 1;85(1-2):167-172
  • "We report that the IIIc transcriptional alternative of Fgfr2 is transcribed in the unfertilized egg and that during early zygotic transcription, messages encoded by both Fgfr2 alternatives (IIIc and IIIb) are present. The Fgfr2 protein was first detected in peripheral blastomeres of compacted morulae. Trophectoderm specificity of Fgfr2 became obvious in the early blastocyst and with maturation its localization underwent further specification, Fgfr2 concentration increased at the abembryonic pole and decreased at the embryonic pole. Moreover Fgfr2 expression became markedly asymmetrical along the animal-vegetal axis of the mature blastocyst. Our observations indicate a role for Fgfr2 in trophectoderm growth and specification and in the orientation and polarity of the preimplantation conceptus."
• Development of cellular polarity of hamster embryos during compaction. Suzuki H, Azuma T, Koyama H, Yang X Biol Reprod 1999 Aug;61(2):521-6
  • "Development of cellular polarity is an important event during early mammalian embryo development and differentiation. Blastomeres of hamster embryos at various stages were examined by scanning electron microscopy (SEM) and immunocytochemical staining. SEM observations revealed that 1- to 7-cell-stage embryos showed a uniform distribution of microvilli throughout the cell surface. Microvillous polarization was initially noted in the blastomeres (10-35%) of 8-cell-stage embryos. The polarized microvilli were observed mostly in the basal region of cell-cell contact and occasionally at the apical, outward-facing surface of the blastomere. Fluorescein-isothiocyanate-conjugated concanavalin A failed to reveal any polarity in the blastomeres regardless of the stages of the embryos. Actin staining showed that microfilaments were present beneath the cell surface, and in addition, areas of cell contact were more heavily stained, indicating a thick microfilament domain. Microtubules were located throughout the cytoplasm and were heavily concentrated near the nucleus during interphase, although they became redistributed in the region of the mitotic spindle during karyokinesis. The position of nucleus changed from the cell center to the apical, outward-facing surface of the cell, and it distanced itself from the basal microvillous pole. It is suggested that the changes in the cell surface and nuclear position are the first manifestations of cell polarity in peri-compacted hamster embryos, which appear as early as the 8-cell stage; furthermore, the outward migration of the nuclei may parallel the redistribution of microtubules in the cytoplasm."

  Search PubMed

  Search May 2006 "blastocyst development" 8,126 reference articles of which 790 were reviews.

  Search PubMed Now: term = blastocyst+development

Glossary of Terms

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

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