Repression of zygotic gene expression in the Xenopus germline

Thiagarajan Venkatarama, Fangfang Lai, Xueting Luo, Yi Zhou, Karen Newman, Mary Lou King

Research output: Contribution to journalArticlepeer-review

56 Scopus citations


Primordial germ cells (PGCs) in Xenopus are specified through the inheritance of germ plasm. During gastrulation, PGCs remain totipotent while surrounding cells in the vegetal mass become committed to endoderm through the action of the vegetal localized maternal transcription factor VegT. We find that although PGCs contain maternal VegT RNA, they do not express its downstream targets at the mid-blastula transition (MBT). Transcriptional repression in PGCs correlates with the failure to phosphorylate serine 2 in the carboxy-terminal domain (CTD) of the large subunit of RNA polymerase II (RNAPII). As serine 5 is phosphorylated, these results are consistent with a block after the initiation step but before the elongation step of RNAPII-based transcription. Repression of PGC gene expression occurs despite an apparently permissive chromatin environment. Phosphorylation of CTD-serine 2 and expression of zygotic mRNAs in PGCs are first detected at neurula, some 10 hours after MBT, indicating that transcription is significantly delayed in the germ cell lineage. Significantly, Oct-91, a POU subclass V transcription factor related to mammalian Oct3/4, is among the earliest zygotic transcripts detected in PGCs and is a likely mediator of pluripotency. Our findings suggest that PGCs are unable to respond to maternally inherited endoderm determinants because RNAPII activity is transiently blocked while these determinants are present. Our results in a vertebrate system further support the concept that one strategy used repeatedly during evolution for preserving the germline is RNAPII repression.

Original languageEnglish (US)
Pages (from-to)651-660
Number of pages10
Issue number4
StatePublished - Feb 15 2010
Externally publishedYes


  • Germ plasm
  • Germline determination
  • Oogenesis
  • Pol II
  • Transcriptional repression
  • Xenopus

ASJC Scopus subject areas

  • Developmental Biology
  • Molecular Biology


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