What is Genomic imprinting
?? A paternal contribution to
embryogenesis
It
is evident through a number of studies about the paternal contribution to embryogenesis.
Genomic imprinting could be one of the paternal factors involved in
embryogenesis, because most of the genes involved in embryo growth and
development are imprinted, i.e. they are expressed from one specific
parental
allele. Our earlier studies on the effect of tamoxifen, a selective estrogen receptor
modulator, on fertility of adult male rats have shown an increase in early
post-implantation embryo loss in females mated with the tamoxifen treated males.
The sperm fertilizing ability was not affected. These studies suggested that
paternal tamoxifen treatment affected embryogenesis. Further studies were done
to understand the mechanism of increased embryo loss. The effect on the
expression
of Igf2, a major growth–promoting factor in the early embryo was studied in the
normal and resorbed embryos (post-implantation loss). It was observed that
resorbed embryos showed significant reduction in Igf2 transcript.
Igf2
is an imprinted gene expressed in the early embryo from the paternal allele.
The
paternal specific expression of Igf2 is due to the differential DNA methylation
of an imprinting control region (ICR) located downstream of Igf2 gene on the
two parental allele during gametogenesis. The ICR also controls the expression
of a reciprocally imprinted gene, H19. On the paternal allele the ICR
is methylated and so
Igf2 is expressed whereas on
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