Daz- and Pumilio-Like Genes Are Asymmetrically Localized in Pelophylax (Rana) Oocytes and Are Expressed During Early Spermatogenesis

In many organisms the specification of cell fate and the formation of embryonic axes depend on a proper distribution of maternal mRNAs during oogenesis. Asymmetrically localized determinants are required both for embryonic axes and germline determination in anuran amphibians. As a model system of these processes, we have used a species complex of the genus Pelophylax (Rana), characterized by a hybridogenetic reproduction that involves events of genome exclusion and endoreduplication. With the aim to analyse the still poorly explored molecular events regulating the Pelophylax gametogenesis, we have isolated in this animal model homologues of DAZl and pumilio gene families (named RlDazl and RlPum1, respectively) that encode post-transcriptional regulators. Expression pattern analysis of these genes showed that RlDazl is exclusively expressed in gonadal tissues, while RlPum1 is expressed in both somatic tissues and gonads. In situ hybridization carried out on gonads, revealed that the two transcripts were asymmetrically localized along the animal-vegetal (A-V) axis of oocytes. In particular, the RlDazl transcript was progressively localized to the vegetal pole during oogenesis, whereas the RlPum1 mRNA was preferentially enriched at the animal hemisphere. In adult testes RlDazl and RlPum1 were expressed in specific phases of spermatogenetic divisions as showed by immunostaining with anti-H3 phosphoistone antibody. Our results indicate that RlDazl and RlPum1 represent two early indicators of oocyte polarity in this hybridogenetic vertebrate model. Additionaly, RlDazl share with vertebrate DAZ-like genes a germ cell-specific expression pattern.