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 [7]
Blastocyst Metabolism
At the blastocyst stage, mammalian development metabolism switches on anaerobic glycolysis metabolism to satisfy metabolic demands of growing blastocyst and formation of the blastocoel. This is thought to be driven by the integral membrane protein family of facilitative glucose transporters (GLUT or SLC2A).
- aerobic - oxidation of lactate and pyruvate via the citric acid cycle (Krebs cycle) and oxidative phosphorylation
- glycolysis- converts glucose into pyruvate
- GLUT - GLUcose Transporter (divided into 3 classes I-III)
- SLC2 - Solute Carrier Family 2
Glucose Transporter Expression
- GLUT1 - from zygote to blastocyst. (all mammalian tissues, basal glucose uptake)
- GLUT2 and GLUT3 - from late eight cell stage to blastocyst. (GLUT2, liver and pancreatic beta cells; GLUT3, all mammalian tissues, basal glucose uptake)
- GLUT4 - not expressed. (muscle and adipose tissue)
- GLUT8 - up-regulated at blastocyst stage. (central nervous system and heart)
- (Data mainly from mouse development, adult tissue expression shown in brackets)
A mouse study,[8] has shown GLUT8 is up-regulated following insulin stimulation, though a more recent GLUT8 knockout mouse shows normal early embryonic development in the absence of this transporter.[9]
- Links: Biochemistry - glucose transporters | GLUT1 | GLUT2 | GLUT8
Blastocyst Hatching
Physical contractions are a feature of morula and blastocyst development. In the blastocyst, repeated contractions occur after blastocoel formation and the frequency of contractions was greater during the hatching period than in the periods both before and after hatching.[10] Interestingly, the same researchers in this study suggest that the weaker contractions (less than 20% volume reduction) seen have a role in hatching, in contrast to strong contractions (20% or more volume reduction) have the opposite effect of inhibiting hatching. | width=250px|height=235px|controller=true|autoplay=false</qt>
Molecular Factors
Blastocyst in Other SpeciesMouse Blastocyst
Bovine BlastocystReferences
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. Search PubMedSearch April 2010 Search Pubmed: blastocyst development | blastocoel development | inner cell mass development | trophectoderm |
Glossary Links
Cite this page: Hill, M.A. (2024, June 15) Embryology Blastocyst Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Blastocyst_Development
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