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During blastulation, a significant amount of activity occurs within the early embryo to establish [[cell polarity]], [[cell fate determination|cell specification]], [[regional specification|axis formation]], and to regulate [[gene expression]].<ref name=Heasman /> In many animals, such as ''[[Drosophila]]'' and ''[[Xenopus]]'', the [[midblastula|mid blastula transition]] (MBT) is a crucial step in development during which the [[maternal effect|maternal mRNA]] is degraded and control over development is passed to the embryo.<ref name="Tadros 2005">{{cite journal|last=Tadros|first=Wael|author2=Lipshitz, Howard D.|title=Setting the stage for development: mRNA translation and stability during oocyte maturation and egg activation in ''Drosophila'' |journal=Developmental Dynamics|date=1 March 2004|volume=232|issue=3|pages=593–608|doi=10.1002/dvdy.20297|pmid=15704150}}</ref> Many of the interactions between blastomeres are dependent on [[cadherin]] expression, particularly [[CDH1 (gene)|E-cadherin]] in mammals and EP-cadherin in [[amphibian]]s.<ref name=Heasman>{{cite journal|last=Heasman|first=J|title=Patterning the ''Xenopus'' blastula |journal=Development|date=November 1997|volume=124|issue=21|pages=4179–91|pmid=9334267|url=http://dev.biologists.org/content/124/21/4179.long}}</ref>
The study of the blastula and of cell specification has many implications in [[embryonic stem cells|stem cell]] research and [[assisted reproductive technology]].<ref name=Cockburn /> In ''Xenopus'', blastomeres behave as [[Cell potency|pluripotent]] stem cells which can migrate down several pathways, depending on [[cell signaling]].<ref name=Gurdon>{{cite journal|last=Gourdon|first=John B.|author2=Standley, Henrietta J.|title=Uncommitted ''Xenopus'' blastula cells can be directed to uniform muscle gene expression by gradient interpretation and a community effect|journal=The International Journal of Developmental Biology (Cambridge, UK)|volume=46|issue=8|pages=993–8|pmid=12533022|url=http://www.ijdb.ehu.es/web/paper.php?doi=12533022|date=December 2002}}</ref> By manipulating the cell signals during the blastula stage of development, various [[Tissue (biology)|tissue]]s can be formed. This potential can be instrumental in [[regenerative medicine]] for disease and injury cases. [[In vitro fertilisation]] involves implantation of a blastula into a mother's uterus.<ref name=Toth>{{cite web|last=Toth|first=Attila|title=Treatment: Addressing the Causes of Infertility in Men and Women|url=http://www.fertilitysolution.com/Infertility/Treatment.html|publisher=Macleod Laboratory|
== Development ==
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