ABSTRACT
Cloned animals often suffer from loss of development to term and abnormalities, typically classified under the umbrella term of Large Offspring Syndrome (LOS). Cattle are an interesting species to study because of the relatively greater success rate of nuclear transfer in this species compared with all species cloned to date. The imprinted insulin-like growth factor receptor (IGF2R; mannose-6-phosphate) gene was chosen to investigate aspects of fetal growth and development in cloned cattle in the present study. IGF2R gene expression patterns in identical genetic clones of several age groups were assessed in day 25, day 45, and day 75 fetuses as well as spontaneously aborted fetuses, calves that died shortly after birth and healthy cloned calves using single stranded conformational polymorphism gel electrophoresis. A variable pattern of IGF2R allelic expression in major organs such as the brain, cotyledon, heart, liver, lung, spleen, kidney and intercotyledon was observed using a G/A transition in the 3'UTR of IGF2R. IGF2R gene expression was also assessed by real time RT-PCR and found to be highly variable among the clone groups. Proper IGF2R gene expression is necessary for survival to term, but is most likely not a cause of early fetal lethality or an indicator of postnatal fitness. Contrary to previous reports of the transmission of imprinting patterns from somatic donor cells to cloned animals within organs in the same cloned animal the paternal allele of IGF2R can be imprinted in one tissue while the maternal allele is imprinted in another tissue. This observation has never been reported in any species in which imprinting has been studied.
