Blastocyst Development
Introduction
(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: Fertilization | Week 1 | Morula | Blastocyst
Some Recent Findings
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Movies
Human Blastocyst Development (day 3-6)
Quicktime version | Flash version
Blastocyst Formation (in vitro)
The table below shows human blastocyst in vitro changes during week 1 development.[4]
Model Human Blastocyst Development
The following figure is from a recent study[2] using video and genetic analysis of in vitro human development during week 1 following fertilization.
- EGA - embryonic genome activation
- ESSP - embryonic stage–specific pattern, four unique embryonic stage–specific patterns (1-4)
- Links: Figure with legend
Mouse Blastocyst Gene Expression
General gene expression patterns are indicated from genomic profiling.[5]
- red - loss of maternal mRNAs
- green - activation of embryonic genome (EGA)
- purple - maternal gene activation (MGA)
- orange - continuous expression
Inner Cell Mass
This outer layer of cells is also called the "embryoblast", a cluster of cells located and attached on one wall of the outer trophoblast layer.
Trophoblast Layer
This outer layer of cells is also called the "trophectoderm" (TE) epithelium. A key function is for the transport of sodium (Na+) and chloride (Cl-) ions through this layer into the blastocoel.
Differentiation of this layer has been shown to be regulated by the transcription factors Tead4[6] and then Caudal-related homeobox 2 (Cdx2).
- Links: Trophoblast | OMIM -Tead4 | OMIM - Cdx2
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 [8]
Molecular Factors
- TEA DNA- binding domain, these factors bind to the consensus TEA/ATTS cognate binding site[9]
- TEF-3 - renamed Tead1 and Tead4
- Tead3 - is expressed in the placental syncytiotrophoblasts
- 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
Blastocyst in Other Species
Mouse Blastocyst
Sox2 expression[10]
Early gene expression[10]
Early gene expression[10]
Early gene expression[10]
Early gene expression[10]
Bovine Blastocyst
References
- ↑ <pubmed>19924284</pubmed>| PMC2773928 | PLoS One
- ↑ 2.0 2.1 <pubmed>20890283</pubmed>| Nat Biotechnol.
- ↑ <pubmed>20864103</pubmed>
- ↑ <pubmed>10221713</pubmed>
- ↑ <pubmed>19043080</pubmed>| Mol Hum Reprod.
- ↑ <pubmed>18083014</pubmed>
- ↑ <pubmed>19043080</pubmed>| Mol Hum Reprod.
- ↑ <pubmed>16139691</pubmed>
- ↑ <pubmed>8702974</pubmed>
- ↑ 10.0 10.1 10.2 10.3 10.4 <pubmed>21103067</pubmed>| PMC2980489 | PLoS One.
Reviews
<pubmed>20607796</pubmed> <pubmed>20364097</pubmed> <pubmed>17389140</pubmed>
Articles
<pubmed>20157423</pubmed> <pubmed>19289087</pubmed> <pubmed>18817772</pubmed> <pubmed>18083014</pubmed> <pubmed>16773657</pubmed>| Dev. Dyn.
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Cite this page: Hill, M.A. (2024, June 16) Embryology Blastocyst Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Blastocyst_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G