Mouse Dazl and its novel splice variant functions in translational repression of target mRNAs in embryonic stem cells

Dazl (deleted in azoospermia-like) is an RNA binding protein that is important for germ cell differentiation in vertebrates. In the present study, we report the identification of a novel Dazl isoform (Dazl_Δ8) that results from alternative splicing of exon8 of mouse Dazl. We observed the expression of Dazl_Δ8 in various pluripotent cell types, but not in somatic cells. Furthermore, the Dazl_Δ8 splice variant was expressed along with the full-length isoform of Dazl (Dazl_FL) throughout male germ-cell development and in the ovary. Sub-cellular localization studies of Dazl_Δ8 revealed a diffused cytoplasmic and large granular pattern, which is similar to the localization patterns of Dazl_FL protein. In contrast to the well documented translation stimulation function in germ cells, overexpression and downregulation studies of Dazl isoforms (Dazl_FL and Dazl_Δ8) revealed a role for Dazl in the negative translational regulation of Mvh, a known target of Dazl, as well as Oct3/4 and Sox2 in embryonic stem cells (ESCs). In line with these observations, a luciferase reporter assay with the 3'UTRs of Oct3/4 and Mvh confirmed the translational repressive role of Dazl isoforms in ESCs but not in germ cells derived cell line GC-1. Further, we identified several putative target mRNAs of Dazl_FL and Dazl_Δ8 in ESCs through RNA-binding immunoprecipitation followed by whole genome transcriptome analysis. Collectively, our results show a translation repression function of Dazl in pluripotent stem cells.