pEg6, a spire family member, is a maternal gene encoding a vegetally localized mRNA in Xenopus embryos.

BACKGROUND INFORMATION: In Xenopus, during oocyte maturation and the segmentation period, cell cycle progression is independent of new transcription, but requires de novo translation. This suggests that the completion of oocyte maturation and then the rapid cell division period is controlled exclusively at a post-transcriptional level by specific gene products. To isolate these maternal genes, a differential screening of a Xenopus egg cDNA library was performed. Several cDNAs were isolated which correspond to mRNA polyadenylated in eggs and deadenylated in embryos, and these constitute the founders members of the Eg family of mRNAs. RESULTS: We report here the characterization of Eg6 mRNA as a novel maternal gene expressed in Xenopus egg until gastrula stage. The Eg6 transcript is initially concentrated in the vegetal cytoplasm of the egg, and later the distribution of the transcript marks the posterior vegetal end of developing embryos. pEg6 is a multidomain protein with a kinase non-catalytic C-lobe domain of unknown function, a cluster of four WH2 (Wiskott-Aldrich syndrome protein homology 2) domains and a modified FYVE zinc-finger motif. The amino acid sequence of pEg6 is related to PEM-5 (posterior end mark-5), from an ascidian maternal mRNA, and spire, a Drosophila protein required to establish dorsal-ventral and anterior-posterior axes of polarity and recently described as an actin nucleation factor. In Xenopus and Schizosaccharomyces pombe cells pEg6 expression induces filamentous actin clusters and is associated with vesicular structure. CONCLUSION: These data suggest that pEg6 acts as a vegetally localized factor contributing to the actin nucleation process during Xenopus early development.

Characterization of the poly(A) binding proteins expressed during oogenesis and early development of Xenopus laevis.

During vertebrate oogenesis and early embryogenesis, gene expression is governed mainly by translational control. The recruitment of Poly(A) Binding Protein (PABP) during poly(A) tail lengthening appears to be the key to translational activation during this period of development in Xenopus laevis. We showed that PABP1 and ePABP proteins are both present during oogenesis and early development. We selected ePABP as an eRF3 binding protein in a two-hybrid screening of a X. laevis cDNA library and demonstrated that this protein is associated with translational complexes. It can complement essential functions of the yeast homologue Pab1p. We discuss specific expression patterns of the finely tuned PABP1 and ePABP proteins.

MOLECULAR AND REPRODUCTIVE CHARACTERIZATION OF SIBLING SPECIES IN THE EUROPEAN EARWIG (FORFICULA AURICULARIA).

The European earwig (Forficula auricularia) was formerly thought to present a mosaic of populations differing in their reproductive biology. We show that it is comprised of two as yet unrecognized sibling species. The molecular divergence between the two species, for a 627-bp amplified fragment overlapping the COI and COII mitochondrial loci, is six times larger than intraspecific variation. A species with two clutches a year lives predominantly in lowland and oceanic European habitats. A species with one clutch a year-except in the Mediterranean area where it has two clutches-lives predominantly in highland and continental European habitats. They both invaded North America during the 20th century, respectively, from the west and the east coasts, with no apparent mixing of their populations. The two species can occur in sympatry in Europe and are reproductively isolated by nearly complete failure to produce F1 hybrids.