The role of the X chromosome in mammalian extra embryonic development.
Accumulating evidence points to the importance of the X chromosome for trophoblast development. In rodents, the extraembryonic cell lineage differs from somatic tissues in that X chromosome inactivation is imprinted, preferentially silencing the paternal X chromosome. As a consequence, trophoblast development is extremely susceptible to deviations from normal X inactivation and is impaired in situations of increased and reduced X-linked gene dosage. Mouse mutants have also shown that maintenance of X chromosome silencing in extraembryonic tissues requires a special set of heterochromatin proteins. Moreover, the X chromosome has been implicated in causing several malformations of the placenta. The observed importance of the X chromosome for placental development can be explained by the presence of many trophoblast-expressed genes, especially in the proximal and central regions. Given that the placenta represents a postzygotic barrier to reproduction, evolutionary constraints may be responsible for the presence of placental genes on the X chromosome that are often co-expressed in brain and testis.
Hemberger
M
M
Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, Alberta, Canada. mhemberg@ucalgary.ca
D000818:Animals; D004303:Dosage Compensation, Genetic; D005314:Embryonic and Fetal Development / Q000235:genetics*; D005260:Female; D018507:Gene Expression Regulation, Developmental; D051379:Mice; D010920:Placenta / Q000378:metabolism; D010929:Placentation; D011247:Pregnancy; D014960:X Chromosome / Q000235:genetics*