DAZL Regulates Germ Cell Survival through a Network of PolyA-Proximal mRNA Interactions

Gene expression patterns and protein cellular localization suggest a novel role for DAZL in developing Tibetan sheep testes

Deleted in azoospermia-like (DAZL) is essential for mammalian spermatogenesis as it regulates proliferation, development, maturation and functional maintenance of male germ cells. Its expression and regulation vary with different species or in the same animal at different developmental stages, and despite its importance, very little is known about its roles in sheep, especially Tibetan sheep. To investigate the expression patterns and regulatory roles of DZAL in Tibetan sheep testis, testicular tissue was isolated from sheep at three crucial development stages: 3 months old, 1 year old and 3 years old. Using quantitative real-time PCR and Western blot, we found that DAZL mRNA first decreased and then increased with advancing age, while DAZL protein exhibited an opposite expression pattern, with first increased and subsequently decreased levels. Immunohistochemistry and immunofluorescence revealed that DAZL protein was located predominantly in the cytoplasm of Leydig cells and in both the cytoplasm and nucleus of spermatids. ELISA indicated that testosterone content within developing testes was first enhanced and then declined. Our results, taken together, demonstrate, for the first time, that DAZL gene is involved in Tibetan sheep spermatogenesis by regulating the development of spermatids in post-pubertal rams, along with a novel role in functional maintenance of Leydig cells in postnatal rams.

Dynamic and regulated TAF gene expression during mouse embryonic germ cell development

Germ cells undergo many developmental transitions before ultimately becoming either eggs or sperm, and during embryonic development these transitions include epigenetic reprogramming, quiescence, and meiosis. To begin understanding the transcriptional regulation underlying these complex processes, we examined the spatial and temporal expression of TAF4b, a variant TFIID subunit required for fertility, during embryonic germ cell development. By analyzing published datasets and using our own experimental system to validate these expression studies, we determined that both Taf4b mRNA and protein are highly germ cell-enriched and that Taf4b mRNA levels dramatically increase from embryonic day 12.5–18.5. Surprisingly, additional mRNAs encoding other TFIID subunits are coordinately upregulated through this time course, including Taf7l and Taf9b. The expression of several of these germ cell-enriched TFIID genes is dependent upon Dazl and/or Stra8, known regulators of germ cell development and meiosis. Together, these data suggest that germ cells employ a highly specialized and dynamic form of TFIID to drive the transcriptional programs that underlie mammalian germ cell development.

Assisted reproductive therapy and fertility preservation are increasingly used to improve human reproduction across the world, yet there are still many unanswered questions regarding what factors govern the development of eggs and sperm and how these factors work together. We previously identified a subunit of the general transcription factor TFIID, TAF4b, that is essential for fertility. However, many basic characteristics of how Taf4b and its associated TFIID family members contribute to the formation of healthy sperm and eggs in mice and humans remain unknown. In this study, we find that mouse Taf4b and several closely related TFIID subunits become highly abundant during mouse embryonic gonad development, specifically in the cells that ultimately become eggs and sperm. Here, we analyzed data from public repositories and isolated these developing cells to examine their gene expression patterns throughout embryonic development. Together these data suggest that the dynamic expression of Taf4b and other TFIID family members are dependent on the well-established reproductive cell regulators Dazl and Stra8. This understanding of Taf4b gene expression and regulation in mouse reproductive cell development is likely conserved during development of human cells and offers novel insights into the interconnectedness of the factors that govern the formation of healthy eggs and sperm.

Approaches for measuring the dynamics of RNA-protein interactions

RNA-protein interactions are pivotal for the regulation of gene expression from bacteria to human. RNA-protein interactions are dynamic; they change over biologically relevant timescales. Understanding the regulation of gene expression at the RNA level therefore requires knowledge of the dynamics of RNA-protein interactions. Here, we discuss the main experimental approaches to measure dynamic aspects of RNA-protein interactions. We cover techniques that assess dynamics of cellular RNA-protein interactions that accompany biological processes over timescales of hours or longer and techniques measuring the kinetic dynamics of RNA-protein interactions in vitro. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA Interactions with Proteins and Other Molecules > Protein-RNA Recognition RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes RNA Evolution and Genomics > Ribonomics.

DAZL is a master translational regulator of murine spermatogenesis

Expression of DAZ-like (DAZL) is a hallmark of vertebrate germ cells, and is essential for embryonic germ cell development and differentiation, yet the gametogenic function of DAZL has not been fully characterized and most of its in vivo direct targets remain unknown. We showed that postnatal stage-specific deletion of Dazl in mouse germ cells did not affect female fertility, but caused complete male sterility with gradual loss of spermatogonial stem cells, meiotic arrest and spermatid arrest. Using the genome-wide high-throughput sequencing of RNAs isolated by cross-linking immunoprecipitation and mass spectrometry approach, we found that DAZL bound to a large number of testicular mRNA transcripts (at least 3008) at the 3'-untranslated region and interacted with translation proteins including poly(A) binding protein. In the absence of DAZL, polysome-associated target transcripts, but not their total transcripts, were significantly decreased, resulting in a drastic reduction of an array of spermatogenic proteins and thus developmental arrest. Thus, DAZL is a master translational regulator essential for spermatogenesis.

Efficient GFP-labeling and analysis of spermatogenic cells using the IRG transgene and flow cytometry

Spermatogenesis is a highly ordered developmental program that produces haploid male germ cells. The study of male germ cell development in the mouse has provided unique perspectives into the molecular mechanisms that control cell development and differentiation in mammals, including tissue‐specific gene regulatory programs. An intrinsic challenge in spermatogenesis research is the heterogeneity of germ and somatic cell types present in the testis. Techniques to separate and isolate distinct mouse spermatogenic cell types have great potential to shed light on molecular mechanisms controlling mammalian cell development, while also providing new insights into cellular events important for human reproductive health. Here, we detail a versatile strategy that combines Cre‐lox technology to fluorescently label germ cells, with flow cytometry to discriminate and isolate germ cells in different stages of development for cellular and molecular analyses.