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Y-box proteins are a highly conserved family of gene expression regulatory factors. During gametogenesis they may play a dual role, as both transcriptional activators of germ cell-specific genes and as translational repressors of stored maternal transcripts. We report the identification of RlYB2, a Y-box homolog gene specifically expressed in the germ cells of green frogs belonging to Rana esculenta complex, a model system characterized by a hybridogenetic gametogenesis. In developing germ cells of the hybrid R. esculenta, arisen by natural cross of the parental species R. ridibunda and R. lessonae, one set of the parental genomes is excluded and the remaining one, first endoreduplicates and then is transmitted to gametes. In situ hybridizations performed on gonadal tissues showed that the RlYB2 transcript was widely expressed in the ooplasm at early stages of oogenesis in both the parental species and hybrids. Interestingly, a hybridization signal, presumably related to RlYB2-like nascent transcripts, was observed in nuclei of stage II oocytes. The presence of RlYB2 mRNA during early oogenesis suggests that this gene may be involved in regulating the transcription and/or translation of maternal mRNAs in this special vertebrate model system. [ABSTRACT FROM AUTHOR]

A family of interspersed repetitive elements, RlBamHI, with sequence similarity to the transposase of hAT DNA transposons, occurs in genomes of eight western Palaearctic water frog taxa and the brown frog Rana dalmatina, but was not detected in Xenopus laevis or Salamandra salamandra. RlBamHI elements are not tandemly arrayed, are dispersed across all chromosomes although not uniformly distributed, and based on dot-blot hybridizations may constitute as much as approximately 10% of the genomes of Rana lessonae, Rana ridibunda, and Rana perezi, but only approximately 1% of that of Rana saharica. Eleven nucleotide sequences of a 572 bp fragment from the nine taxa are very similar (pairwise differences 0.4–8.1% for nucleotides, 0.6–18.2% for amino acids), and all share a single open reading frame across the whole RlBamHI fragment. The reading frame is maintained despite several indels, most of which are multiples of 3 bp, but a pair of which in one species alters and, after 13 codons, restores the reading frame. It is possible that the reading frame is selectively maintained, suggesting recent or even present transposition capacity. The amino acid sequences encoded by RlBamHI elements, but not the nucleotide sequences themselves, reveal the similarity of RlBamHI to members of the widespread hAT superfamily of DNA transposons. Amino acid sequence comparisons permitted no convincing phylogenetic placement of RlBamHI among 32 representative hAT transposons across organisms, probably reflecting both the genetic divergence of RlBamHI elements and the paucity of aligned residues available for analysis. Among DNA transposons, a genomic fraction of 10% is extraordinarily high. Phylogenetic analyses of Rana RlBamHI sequences match poorly with independent genetic and molecular phylogenies; the elements compared probably are not orthologous, which renders their sequences inadequate for reconstructing organismal phylogenetic histories. [ABSTRACT FROM AUTHOR]