Maternal to zygotic transition

Maternal to zygotic transition (MZT), also known as embryonic genome activation, is the stage in embryonic development during which development comes under the exclusive control of the zygotic genome rather than the maternal (egg) genome. The egg contains stored maternal genetic material mRNA which controls embryo development until the onset of MZT. After MZT the diploid embryo takes over genetic control.[1][2] This requires both zygotic genome activation (ZGA), and degradation of maternal products. This process is important because it is the first time that the new embryonic genome is utilized and the paternal and maternal genomes are used in combination (ie. different alleles will be expressed). The zygotic genome now drives embryo development.

MZT is often thought to be synonymous with midblastula transition (MBT), but these processes are, in fact, distinct.[3] However, the MBT roughly coincides with ZGA in many metazoans,[4] and thus may share some common regulatory features. For example, both processes are proposed to be regulated by the nucleocytoplasmic ratio.[5][6] MBT strictly refers to changes in the cell cycle and cell motility that occur just prior to gastrulation.[3][4] In the early cleavage stages of embryogenesis, rapid divisions occur synchronously and there are no "gap" stages in the cell cycle.[3] During these stages, there is also little to no transcription of mRNA from the zygotic genome,[5] but zygotic transcription is not required for MBT to occur.[3] Cellular functions during early cleavage are carried out primarily by maternal products – proteins and mRNAs contributed to the egg during oogenesis.

  1. ^ Lee MT, Bonneau AR, Takacs CM, Bazzini AA, DiVito KR, Fleming ES, Giraldez AJ (November 2013). "Nanog, Pou5f1 and SoxB1 activate zygotic gene expression during the maternal-to-zygotic transition". Nature. 503 (7476): 360–4. doi:10.1038/nature12632. PMC 3925760. PMID 24056933.
  2. ^ Schulz KN, Harrison MM (April 2019). "Mechanisms regulating zygotic genome activation". Nat Rev Genet. 20 (4): 221–234. doi:10.1038/s41576-018-0087-x. PMC 6558659. PMID 30573849.
  3. ^ a b c d Baroux C, Autran D, Gillmor CS, et al. (2008). "The Maternal to Zygotic Transition in Animals and Plants". Cold Spring Harb Symp Quant Biol. 73: 89–100. doi:10.1101/sqb.2008.73.053. PMID 19204068.
  4. ^ a b Tadros W, Lipshitz HD (2009). "The maternal to zygotic transition: a play in two acts". Development. 136 (18): 3033–42. doi:10.1242/dev.033183. PMID 19700615.
  5. ^ a b Newport J, Kirschner M (1982). "A major developmental transition in early Xenopus embryos: I. characterization and timing of cellular changes at the midblastula stage". Cell. 30 (3): 675–86. doi:10.1016/0092-8674(82)90272-0. PMID 6183003. S2CID 24114437.
  6. ^ Pritchard DK, Schubiger G (1996). "Activation of transcription in Drosophila embryos is a gradual process mediated by the nucleocytoplasmic ratio". Genes Dev. 10 (9): 1131–42. doi:10.1101/gad.10.9.1131. PMID 8654928.