Abstract
Mammalian uniparental embryos are efficient models for genome imprinting research and allow studies on the contribution of the paternal and maternal genomes to early embryonic development. In this study, we analyzed different methods for production of bovine haploid androgenetic embryos (hAE) to elucidate the causes behind their poor developmental potential. Results indicate that hAE can be efficiently generated by using intracytoplasmic sperm injection and oocyte enucleation at telophase II. Although androgenetic haploidy does not disturb early development up to around the 8-cell stage, androgenetic development is disturbed after the time of zygote genome activation and hAE that reach the morula stage are less capable to reach the blastocyst stage of development. Karyotypic comparisons to parthenogenetic- and ICSI-derived embryos excluded chromosomal segregation errors as causes of the developmental constraints of hAE. However, analysis of gene expression indicated abnormal levels of transcripts for key long non-coding RNAs involved in X chromosome inactivation and genomic imprinting of the KCNQ1 locus, suggesting an association with X chromosome and some imprinted loci. Moreover, transcript levels of methyltransferase 3B were significantly downregulated, suggesting potential anomalies in hAE establishing de novo methylation. Finally, the methylation status of imprinted control regions for XIST and KCNQ1OT1 genes remained hypomethylated in hAE at the morula and blastocyst stages, confirming their origin from spermatozoa. Thus, our results exclude micromanipulation and chromosomal abnormalities as major factors disturbing the normal development of bovine haploid androgenotes. In addition, although the cause of the arrest remains unclear, we have shown that the inefficient development of haploid androgenetic bovine embryos to develop to the blastocyst stage is associated with abnormal expression of key factors involved in X chromosome activity and genomic imprinting.
Highlights
In contrast to lower animal classes that can develop from a single parent by parthenogenesis, mammals have developed parentalspecific epigenetic strategies such as genomic imprinting that require the contribution from the paternal and maternal genomes for the embryo to develop fully to term
Since the ratio of haploid parthenogenetic morulae (68%) that become blastocyst was significantly higher (p < 0.005) than the haploid androgenetic group, these results indicate that, as in the other mammalian models, the bovine haploid paternal condition is less capable to support early embryonic development compared to its maternal counterpart
Since the KCNQ1 differentially methylated regions (DMR) in haploid androgenetic embryos (hAE) maintains the hypomethylated patterns found in sperm, these results indicate that androgenetic haploidy leads to the dysregulation of the paternal-specific long non-coding transcript and other imprinted genes from the KCNQ1 locus by epigenetic mechanisms other than the methylation status of its DMR
Summary
In contrast to lower animal classes that can develop from a single parent by parthenogenesis, mammals have developed parentalspecific epigenetic strategies such as genomic imprinting that require the contribution from the paternal and maternal genomes for the embryo to develop fully to term. During post-fertilization reprogramming, the embryo loses gamete-specific DNA methylation patterns inherited from the oocyte and the sperm as it progresses toward the blastocyst stage and gain pluripotency, which occurs in two phases. Despite that normal embryonic development requires contributions from both the maternally and paternally inherited haploid genomes, early development can be achieved from uniparental embryos in mammals using artificial oocyte activation and/or micromanipulation techniques, and these have been extremely useful in delineating genomic function, imprinting status and parental-specific roles in ontogenesis (Cruz et al, 2008; Hu et al, 2015b). Haploid development is a normal part of the life cycle for some animals (e.g., parasitic wasps), haploidy in mammals is restricted to gametes, which are structurally specialized for fertilization and mitotically incompetent (Shuai and Zhou, 2014)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
