Putative imprinted gene expression in uniparental bovine embryo models

Abstract

Abstract. Altered patterns of gene expression and the imprinted status of genes have a profound effect on cell physiology and can markedly alter embryonic and fetal development. Failure to maintain correct imprinting patterns can lead to abnormal growth and behavioural problems, or to early pregnancy loss. Recently, it has been reported that the Igf2R and Grb10 genes are biallelically expressed in sheep blastocysts, but monoallelically expressed at Day 21 of development. The present study investigated the imprinting status of 17 genes in in vivo, parthenogenetic and androgenetic bovine blastocysts in order to determine the prevalence of this unique phenomenon. Specifically, the putatively imprinted genes Ata3, Impact, L3Mbtl, Magel2, Mkrn3, Peg3, Snrpn, Ube3a and Zac1 were investigated for the first time in bovine in vitro fertilised embryos. Ata3 was the only gene not detected. The results of the present study revealed that all genes, except Xist, failed to display monoallelic expression patterns in bovine embryos and support recent results reported for ovine embryos. Collectively, the data suggest that monoallelic expression may not be required for most imprinted genes during preimplantation development, especially in ruminants. The research also suggests that monoallelic expression of genes may develop in a gene-and time-dependent manner.

Gene Expression in Early Expanded Parthenogenetic and In Vitro Fertilized Bovine Blastocysts

“…In addition, parthenotes and embryos could differ in terms of the stress signalling that triggers growth arrest and eventually apoptosis, p66 shc being preponderant in parthenotes over p53. The lower expression of CX43 in parthenotes does not correspond to morphological or functional differences between both blastocyst types within Day-8 embryos [7]. Lower expression of OCT3/4 in parthenotes may indicate low pluripotency in such blastocysts.…”

“…In cattle, production of reconstructed embryos by somatic cell nuclear transfer (SCNT) [5] and intracytoplasmic sperm injection (ICSI) [6] depends on successful oocyte activation. Therefore, procedures involving SCNT and ICSI could benefit from a better knowledge of mechanisms that differ between embryos and parthenotes.Contrary to the research in mice and humans, most studies have failed to detect putatively imprinted genes in bovine early development [7,8], suggesting that monoallelic expression may not develop until after Day 21 of development, as occurs in ovine species [9]. In fact, a recent study found imprinted expression of bovine Mest-1 in Day-21 but not Day-14 embryos, while 7 other putatively imprinted genes were shown to be not imprinted at the two stages analyzed [10].…”

“…Contrary to the research in mice and humans, most studies have failed to detect putatively imprinted genes in bovine early development [7,8], suggesting that monoallelic expression may not develop until after Day 21 of development, as occurs in ovine species [9]. In fact, a recent study found imprinted expression of bovine Mest-1 in Day-21 but not Day-14 embryos, while 7 other putatively imprinted genes were shown to be not imprinted at the two stages analyzed [10].…”

“…There are outstanding differences in pregnancy recognition, as judged by the gene panel studied, between Day-7 IVF embryos and parthenotes, as it is intriguing that there is weaker signalling through PGRMC1, although an increase in IFN-τ is typical from the female genotype carried by parthenotes. The differences found between the parthenotes and IVF embryos seem to be associated with the genes involved in placenta formation more than ICM pluripotency, which would support parthenotes as a potential source of stem cells even though they are unable to develop to term.The pro-apoptotic gene expression profile in parthenotes is more pronounced than within IVF embryos, although this is inconsistent with the similar incidence of DNA damage found in Day-8 IVF embryos and parthenotes [7]. In addition, parthenotes and embryos could differ in terms of the stress signalling that triggers growth arrest and eventually apoptosis, p66 shc being preponderant in parthenotes over p53.…”

“…Sagirkaya et al [71] found that DNMT3A expression changes with culture conditions, and we suggest that changes in DNMT3A expression could also be related to develop- GÓMEZ et al 612 ment timing. The distinct difference in gene expression level of DNMT3A between Day-7 and Day-8 parthenotes compared with IVF embryos is nevertheless intriguing, as no imprinted genes have been found until now during bovine early embryonic development [7,8].PLAC8, an invasion specific gene, is more abundant in blastocysts resulting in calf delivery compared with those resulting in resorption [22] and is more abundant in the endometria of pregnant cows compared with non-pregnant cows [72,73]. This suggests a potential role in placental development and the feto-maternal interface.…”