Early embryonic development in mammals begins in transcriptional silence with an oocyte-mediated transcriptional reprogramming of parental gametes occurs during a so called across-the-board process of “erase-and-rebuild”. In this process, the parental transcription programs are erased long before (maternal) or soon thereafter (paternal) fertilization to generate a relatively naïve zygotic chromatin upon which the transcription program of new life cycle is rebuilt de novo after activation of zygotic genome. Any perturbation in either process will result in ill/fatal transcriptional phenotypes of the resultant embryos, and correspondingly, the very few viable clones obtained at the end of a typical cloning experiment underscores substantial differences exist between transcriptional reprogramming of nuclei somatic cells and gametes. Even though, a single defect in transcription reprogramming may cause a “ripple” effect on aberrant expression of entire networks of downstream target genes, and therefore, analysis of a small number of transcripts is of limited value for systematic study of genetic interactions in a complex trait and needs post genomic area approaches including genome wide analyses and network investigation. Here, we review the current status of transcriptomics in understanding oocyte mediated cellular reprogramming to propose that only a limited number of genes deregulated during oocyte mediated reprogramming. Accordingly, we believe that cloning's serendipity lies in great capability of ooplasm to reprogramming almost all genes of somatic cell and cloning unpredictability lie in few certain unstable genes that resist reprogramming.
Materials and methods