Germ cell survival in C. elegans and C. remanei is affected when the DEAD box RNA helicases VBH-1 or Cre-VBH-1 are silenced

Cap-Independent mRNA Translation in Germ Cells

Cellular mRNAs in plants and animals have a 5'-cap structure that is accepted as the recognition point to initiate translation by ribosomes. Consequently, it was long assumed that the translation initiation apparatus was built solely for a cap-dependent (CD) mechanism. Exceptions that emerged invoke structural damage (proteolytic cleavage) to eukaryotic initiation factor 4 (eIF4) factors that disable cap recognition. The residual eIF4 complex is thought to be crippled, but capable of cap-independent (CI) translation to recruit viral or death-associated mRNAs begrudgingly when cells are in great distress. However, situations where CI translation coexists with CD translation are now known. In such cases, CI translation is still a minor mechanism in the major background of CD synthesis. In this review, I propose that germ cells do not fit this mold. Using observations from various animal models of oogenesis and spermatogenesis, I suggest that CI translation is a robust partner to CD translation to carry out the translational control that is so prevalent in germ cell development. Evidence suggests that CI translation provides surveillance of germ cell homeostasis, while CD translation governs the regulated protein synthesis that ushers these meiotic cells through the remarkable steps in sperm/oocyte differentiation.

Cloning and expression analysis of the DEAD-box/RNA helicase Oslaf-1 in Ovomermis sinensis

Ovomermis sinensis is a potentially-valuable nematode for controlling insect pests. The parasitic stage of the nematode absorbs nutrients in its host’s hemolymph to maintain its growth development and then kills the host when it emerges. At present, little known about its reproductive development, particularly the responsible molecular mechanism. More detailed research on the genes of reproductive development will not only help us understand the mechanisms underlying sex differentiation in the nematode, but would also be valuable for successfully cultivating them in vitro and using them for biocontrol. In this study, we used the homology cloning method to clone the full-length cDNA of a DEAD-box family gene (Oslaf-1) from O. sinensis. Then, using qRT-PCR technology to detect the expression pattern of the Oslaf-1 gene at different development stages and tissues, the gene was found to be highly expressed in the post-parasitic stage (P < 0.01) and ovarian (P < 0.05) of O. sinensis. Western blot analysis showed the same result that the gene is associated with gonadal development and function, but is not gonad-specific. In situ hybridization further demonstrated that the gene is widely expressed in early embryos and is mainly distributed in the gonadal area. However, the signal was mainly concentrated in the reproductive primordia in pre-parasitic juveniles. RNA interference (RNAi) studies revealed that the sex ratio of O. sinensis soaked in dsRNA of Oslaf-1 was not statistically different than the gfp dsRNA treated groups. Our results suggest that Oslaf-1 may play a vital role in the reproductive systems of the nematode. In addition, we speculate that the Oslaf-1 gene plays an important role during embryonic development and that it occurs and develops in the gonads of pre-parasitic juveniles of O. sinensis.

vasa and piwi are required for mitotic integrity in early embryogenesis in the spider Parasteatoda tepidariorum

Studies in vertebrate and invertebrate model organisms on the molecular basis of primordial germ cell (PGC) specification have revealed that metazoans can specify their germ line either early in development by maternally transmitted cytoplasmic factors (inheritance), or later in development by signaling factors from neighboring tissues (induction). Regardless of the mode of PGC specification, once animal germ cells are specified, they invariably express a number of highly conserved genes. These include vasa and piwi, which can play essential roles in any or all of PGC specification, development, or gametogenesis. Although the arthropods are the most speciose animal phylum, to date there have been no functional studies of conserved germ line genes in species of the most basally branching arthropod clade, the chelicerates (which includes spiders, scorpions, and horseshoe crabs). Here we present the first such study by using molecular and functional tools to examine germ line development and the roles of vasa and piwi orthologues in the common house spider Parasteatoda (formerly Achaearanea) tepidariorum. We use transcript and protein expression patterns of Pt-vasa and Pt-piwi to show that primordial germ cells (PGCs) in the spider arise during late embryogenesis. Neither Pt-vasa nor Pt-piwi gene products are localized asymmetrically to any embryonic region before PGCs emerge as paired segmental clusters in opisthosomal segments 2-6 at late germ band stages. RNA interference studies reveal that both genes are required maternally for egg laying, mitotic progression in early embryos, and embryonic survival. Our results add to the growing body of evidence that vasa and piwi can play important roles in somatic development, and provide evidence for a previously hypothesized conserved role for vasa in cell cycle progression.

The DEAD Box RNA helicase VBH-1 is a new player in the stress response in C. elegans

For several years, DEAD box RNA helicase Vasa (DDX4) has been used as a bona fide germline marker in different organisms. C. elegans VBH-1 is a close homolog of the Vasa protein, which plays an important role in gametogenesis, germ cell survival and embryonic development. Here, we show that VBH-1 protects nematodes from heat shock and oxidative stress. Using the germline-defective mutant glp-4(bn2) we found that a potential somatic expression of vbh-1 might be important for stress survival. We also show that the VBH-1 paralog LAF-1 is important for stress survival, although this protein is not redundant with its counterpart. Furthermore, we observed that the mRNAs of the heat shock proteins hsp-1 and sip-1 are downregulated when vbh-1 or laf-1 are silenced. Previously, we reported that in C. elegans, VBH-1 was primarily expressed in P granules of germ cells and in the cytoplasm of all blastomeres. Here we show that during stress, VBH-1 co-localizes with CGH-1 in large aggregates in the gonad core and oocytes; however, VBH-1 aggregates do not overlap with CGH-1 foci in early embryos under the same conditions. These data demonstrate that, in addition to the previously described role for this protein in the germline, VBH-1 plays an important role during the stress response in C. elegans through the potential direct or indirect regulation of stress response mRNAs.

Evidence against a germ plasm in the milkweed bug Oncopeltus fasciatus, a hemimetabolous insect

Primordial germ cell (PGC) formation in holometabolous insects like Drosophila melanogaster relies on maternally synthesised germ cell determinants that are asymmetrically localised to the oocyte posterior cortex. Embryonic nuclei that inherit this "germ plasm" acquire PGC fate. In contrast, historical studies of basally branching insects (Hemimetabola) suggest that a maternal requirement for germ line genes in PGC specification may be a derived character confined principally to Holometabola. However, there have been remarkably few investigations of germ line gene expression and function in hemimetabolous insects. Here we characterise PGC formation in the milkweed bug Oncopeltus fasciatus, a member of the sister group to Holometabola, thus providing an important evolutionary comparison to members of this clade. We examine the transcript distribution of orthologues of 19 Drosophila germ cell and/or germ plasm marker genes, and show that none of them localise asymmetrically within Oncopeltus oocytes or early embryos. Using multiple molecular and cytological criteria, we provide evidence that PGCs form after cellularisation at the site of gastrulation. Functional studies of vasa and tudor reveal that these genes are not required for germ cell formation, but that vasa is required in adult males for spermatogenesis. Taken together, our results provide evidence that Oncopeltus germ cells may form in the absence of germ plasm, consistent with the hypothesis that germ plasm is a derived strategy of germ cell specification in insects.