A developmental timer that regulates apoptosis at the onset of gastrulation

Abstract

Recent work identified an apoptotic program in gastrulation stage Xenopus embryos (Anderson, J.A., Lewellyn, A.L., Maller, J.L., 1997. Mol. Biol. Cell 8, 1195-1206; Stack, J.H., Newport, J.W., 1997. Development 124, 3185-3195). Here, we characterize in detail this maternal cell death program, which is set up at fertilization and abruptly activated at the onset of gastrulation, following DNA damage or treatment of embryos with inhibitors of transcription, translation, or replication, between the time of fertilization and the midblastula transition (MBT). This apoptotic pathway is activated under tightly regulated developmental control(s): if the same treatments are applied after the MBT the apoptotic response is abrogated. Embryos displayed many characteristic apoptotic features, including DNA fragmentation, caspase activation, and embryonic death was blocked in vivo by the ectopic expression of Bcl-2, or injection of the caspase-3 inhibitor z-DEVD-fmk. The precise timing and the execution of this maternal cell death program is set at fertilization and does not depend on the type of stress applied, on cell cycle progression, or on de novo protein synthesis. This maternal developmental program might palliate the lack of cell cycle checkpoints in the pre-MBT embryo.

The role of FoxC1 in early Xenopus development

“…Loss of adhesion may occur in Xenopus embryos either because of the specific loss of expression of mRNAs for adhesion proteins (Heasman et al, 1994) or because of a loss of entire transcriptional programs (Hensey and Gautier, 1997;Sible et al, 1997). In the latter case, loss of adhesion is accompanied by apoptosis.…”

Paternal chromosome loss and metabolic crisis contribute to hybrid inviability in Xenopus

“…Embryos were fixed in MEMFA as described for embryo whole mount immunofluorescence and processed as previously described 20 with minor modifications. Briefly, after gradual rehydration, embryos were bleached with 1–2% H 2 O 2 in 0.5X SSC containing 5% formamide for 1–2 h under light.…”

“…Micronuclei in cancer cells accumulate DNA damage 17–19 and, in Xenopus , DNA damage was shown to trigger apoptosis at the onset of gastrulation 20 . As in cancer cells, micronuclei in t e × l s hybrid embryos often lost envelope integrity and contained damaged DNA (Extended Data Fig.…”

XLX is an IAP family member regulated by phosphorylation during meiosis

“…We took advantage of the fact that Xenopus embryos subjected to genotoxic insults undergo highly synchronous apoptosis at the onset of gastrulation, provided the damage was inflicted before the mid-blastula transition. [26][27][28][29] We generated caspase-active cell-free extracts from gastrulation stage embryos that had been treated at the four-cell stage with camptothecin, an inhibitor of DNA topoisomerase I that leads to the generation of double-strand breaks during DNA replication. Caspase activity was monitored by cleavage of 35 S-labeled truncated-PARP ( 35 S-tPARP).…”