Choriogenesis

In developmental biology, choriogenesis is the formation of the chorion, an outer membrane of the placenta that eventually forms chorionic villi that allow the transfer of blood and nutrients from mother to fetus.^[1]

Influence on monozygotic twins

Identical twins have identical genomes in the immediate aftermath of twinning. Two-thirds of monozygotic twins share the same placenta, arising by cleavage before the fourth day of development; the other third have separate placentas because cleavage has taken place after the fourth day after choriogenesis has begun.

Placentas vary with respect to the transport of nutrients and hormones, a variance that may influence epigenesis. For example, the pattern of X chromosome inactivation is affected by placental status. There is some evidence that it affects the variance in IQ test findings among identical twins, that is, monochorionic identical twins display less IQ variance one from another than do dichorionic identical twins. There is weak evidence that monozygotic twins sharing a placenta have a higher concordance rate for schizophrenia than monozygotic twins with separate placentas. Sharing a placenta increases the risk for infection, and infection in pregnancy has been shown to be a risk factor for schizophrenia. Equally striking is evidence for increasing difference in genomic expression between identical twins as they are once again implicating environmental intercession.

References

1. ^ "Choriogenesis". The Mosby Medical Encyclopedia. http://www.highbeam.com/doc/1P1-28729473.html. 

External links

• Irles P, Bellés X, Piulachs MD (2009). "Identifying genes related to choriogenesis in insect panoistic ovaries by Suppression Subtractive Hybridization". BMC Genomics 10: 206. doi:10.1186/1471-2164-10-206. PMC 2683872. PMID 19405973. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2683872. 
• Leclerc RF, Regier JC (November 1993). "Choriogenesis in the Lepidoptera: morphogenesis, protein synthesis, specific mRNA accumulation, and primary structure of a chorion cDNA from the gypsy moth". Developmental Biology 160 (1): 28–38. doi:10.1006/dbio.1993.1283. PMID 8224544. 
• Bellés X, Cassier P, Cerdá X, et al. (April 1993). "Induction of choriogenesis by 20-hydroxyecdysone in the German cockroach". Tissue & Cell 25 (2): 195–204. doi:10.1016/0040-8166(93)90019-H. PMID 18621230. 
• Martínez-Cruzado JC, Swimmer C, Fenerjian MG, Kafatos FC (July 1988). "Evolution of the Autosomal Chorion Locus in Drosophila. I. General Organization of the Locus and Sequence Comparisons of Genes S15 and S19 in Evolutionarily Distant Species". Genetics 119 (3): 663–77. PMC 1203451. PMID 3136055. http://www.genetics.org/cgi/pmidlookup?view=long&pmid=3136055.