Blastocyst Development

From Embryology

Introduction

Blastocyst hatching from zona pellucida (mouse)

(Greek, blastos = sprout + cystos = cavity) or blastula, the term used to describe the hollow cellular mass that forms in early development. The blastocyst consists of cells forming an outer trophoblast layer, an inner cell mass and a fluid-filled cavity. The blastocyst inner cell mass is the source of true embryonic stem cells capable of forming all cell types within the embryo. In humans, this stage occurs in the first and second weeks after the zygote forms a solid cellular mass morula stage) and before implantation.


Links: Week 1

Some Recent Findings

  • Non-invasive imaging of human embryos before embryonic genome activation predicts development to the blastocyst stage[1] "We report studies of preimplantation human embryo development that correlate time-lapse image analysis and gene expression profiling. By examining a large set of zygotes from in vitro fertilization (IVF), we find that success in progression to the blastocyst stage can be predicted with >93% sensitivity and specificity by measuring three dynamic, noninvasive imaging parameters by day 2 after fertilization, before embryonic genome activation (EGA)."
  • Blastocyst gene expression correlates with implantation potential[2] "Compared with blastocysts that resulted in healthy fetal development, blastocysts that failed to implant (negative) showed decreased B3gnt5 and Eomes gene expression, while blastocysts that resulted in spontaneous pregnancy loss (absorption) displayed decreased Wnt3a and Eomes gene expression."

Model Human Blastocyst Development

The following figure is from a recent study[3] using video and genetic analysis of in vitro human development during week 1 following fertilization.

Model human blastocyst development.jpg

  • EGA - embryonic genome activation
  • ESSP - embryonic stage–specific pattern, four unique embryonic stage–specific patterns (1-4)
Links: Figure with legend


Inner Cell Mass

A cluster of cells located and attached on one wall of the outer trophoblast layer, these cells are also called the "embryoblast", as a term to discriminate them from "trophoblast".

Trophoblast Layer

  • trophectoderm epithelium
  • transport of Na+ and Cl- ions through this layer into the blastocoel

Development Processes

Compaction

  • E-cadherin mediated adhesion initiates at compaction at the 8-cell stage
  • regulated post-translationally via protein kinase C and other signalling molecules

Blastocoel Formation

  • trophectoderm transports of Na+ and Cl- ions through this layer into the blastocoel
  • generates an osmotic gradient driving fluid across this epithelium
  • distinct apical and basolateral membrane domains specific for transport
  • facilitates transepithelial Na+ and fluid transport for blastocoel formation
  • transport is driven by Na, K-adenosine triphosphatase (ATPase) in basolateral membranes of the trophectoderm [4]


Molecular Factors

  • E-cadherin - Calcium ion-dependent cell adhesion molecule, a cell membrane adhesive protein required for morula compaction
  • epithin - A type II transmembrane serine protease, identified in mouse for compaction of the morula during preimplantation embryonic development. Expressed from 8-cell stage at blastomere contacts and co-localises in the morula with E-cadherin. PMID: 15848395
  • Na, K-adenosine triphosphatase - A sodium potassium pump that generates an osmotic gradient for fluid flow into the blastocoel
  • Zonula occludens-1 - (ZO-1) Tight junction protein involved in morula to blastocyst transformation in the mouse PMID: 18423437

References

  1. <pubmed>20890283</pubmed>
  2. <pubmed>20864103</pubmed>
  3. <pubmed>20890283</pubmed>| Nat Biotechnol.
  4. <pubmed>16139691</pubmed>


Articles

<pubmed>19289087</pubmed> <pubmed>18817772</pubmed> <pubmed>18083014</pubmed> <pubmed>20157423</pubmed>

Search PubMed

Search April 2010

Search Pubmed: blastocyst development | blastocoel development | inner cell mass development | trophectoderm |


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Cite this page: Hill, M.A. (2021, February 26) Embryology Blastocyst Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Blastocyst_Development

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© Dr Mark Hill 2021, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G