Embryonic genome activation

Abstract

Genome activation is one of the first critical events in the life of the new organism. Both the timing of genome activation and the array of genes activated must be controlled correctly. Genome activation occurs in a stepwise manner, with some genes being transcribed well in advance of the major genome activation event, in which most housekeeping genes become activated. Changes in chromatin protein content, particularly histone proteins, and chromatin structure appear to regulate the availability of the genome for transcription and provide for specificity of transcription. Gene enhancers are not initially required for transcription, but become necessary as the chromatin structure is modified. Changes in transcription factor content or activity are also required, and protein synthesis is essential for genome activation during both early and later phases of transcriptional activation. Both the changes in chromatin structure and availability of transcription factors are regulated by cell cycle-dependent mechanisms, thus providing the necessary coordination between these processes and other processes such as DNA replication and cleavage.

Spermatozoal RNA: why is it there and what does it do?

“…Based on the above reports on DNA and RNA interactions with the spermatozoon, we now have some circumstantial evidence that this differential state of transcriptional poise can potentially be activated in the spermatozoon itself. It is also tempting to speculate there may be a relationship between potentiated gene sequences and genes that are active in the paternal pronucleus of pre-cleavage stage zygotes [52]. The study of Rassoulzadegan et al certainly strengthens the notion that distinct chromatin domains in spermatozoa (in this case, brought about by DNA and/or histone methylation) may be related somehow to spermatozoal RNA carriage and subsequent gene expression in the zygote.…”

Cloning and expression of porcine Dicer and the impact of developmental stage and culture conditions on MicroRNA expression in porcine embryos

“…3.4). Taking into account the timing of mammalian embryonic genome activation, which occurs progressively from the 2-cell stage to the 8-cell stage (Latham and Schultz, 2001), the porcine embryo is likely producing its own Dicer transcript by the blastocyst stage. Further work is necessary to evaluate Dicer expression in other early stage embryos (i.e.…”

A novel marsupial pri-miRNA transcript has a putative role in gamete maintenance and defines a vertebrate miRNA cluster paralogous to the miR-15a/miR-16-1 cluster

“…The miR-290 cluster, expressed extensively in primordial germ cells and spermatogonia (Hayashi et al 2008), has recently been implicated in the maintenance of germline potency (Blakaj & Lin 2008). Moreover, mouse gametes that lack Dicer (the enzyme required for miRNA biogenesis) also showed deficiency in spermatogenesis (Hayashi et al 2008) and chromosomal defects during gametes (Schultz 1993, Latham 1999, Latham & Schultz 2001, but possibly functions primarily on gametes by providing developmental cues necessary for gamete maintenance. During and following dunnart cleavage, pri-miR-16c is no longer required, as suggested by the lack of expression in the uteri and in cleavage-stage conceptuses.…”