Differential Roles of HOW in Male and Female Drosophila Germline Differentiation

The adult gonads in both male and female Drosophila melanogaster produce gametes that originate from a regenerative pool of germline stem cells (GSCs). The differentiation programme that produces gametes must be co-ordinated with GSC maintenance and proliferation in order to regulate tissue regeneration. The HOW RNA-binding protein has been shown to maintain mitotic progression of male GSCs and their daughters by maintenance of Cyclin B expression as well as suppressing accumulation of the differentiation factor Bam. Loss of HOW function in the male germline results in loss of GSCs due to a delay in G2 and subsequent apoptosis. Here we show that female how mutant GSCs do not have any cell cycle defects although HOW continues to bind bam mRNA and suppress Bam expression. The role of HOW in suppressing germ cell Bam expression appears to be conserved between sexes, leading to different cellular outcomes in how mutants due to the different functions of Bam. In addition the role in maintaining Cyclin B expression has not been conserved so female how GSCs differentiate rather than arrest

Phosphorylation of the Drosophila melanogaster RNA–Binding Protein HOW by MAPK/ERK Enhances Its Dimerization and Activity

Drosophila melanogaster Held Out Wings (HOW) is a conserved RNA–binding protein (RBP) belonging to the STAR family, whose closest mammalian ortholog Quaking (QKI) has been implicated in embryonic development and nervous system myelination. The HOW RBP modulates a variety of developmental processes by controlling mRNA levels and the splicing profile of multiple key regulatory genes; however, mechanisms regulating its activity in tissues have yet to be elucidated. Here, we link receptor tyrosine kinase (RTK) signaling to the regulation of QKI subfamily of STAR proteins, by showing that HOW undergoes phosphorylation by MAPK/ERK. Importantly, we show that this modification facilitates HOW dimerization and potentiates its ability to bind RNA and regulate its levels. Employing an antibody that specifically recognizes phosphorylated HOW, we show that HOW is phosphorylated in embryonic muscles and heart cardioblasts in vivo, thus documenting for the first time Serine/Threonine (Ser/Thr) phosphorylation of a STAR protein in the context of an intact organism. We also identify the sallimus/D-titin (sls) gene as a novel muscle target of HOW–mediated negative regulation and further show that this regulation is phosphorylation-dependent, underscoring the physiological relevance of this modification. Importantly, we demonstrate that HOW Thr phosphorylation is reduced following muscle-specific knock down of Drosophila MAPK rolled and that, correspondingly, Sls is elevated in these muscles, similarly to the HOW RNAi effect. Taken together, our results provide a coherent mechanism of differential HOW activation; MAPK/ERK-dependent phosphorylation of HOW promotes the formation of HOW dimers and thus enhances its activity in controlling mRNA levels of key muscle-specific genes. Hence, our findings bridge between MAPK/ERK signaling and RNA regulation in developing muscles

The QKI-6 RNA Binding Protein Regulates Actin-interacting Protein-1 mRNA Stability during Oligodendrocyte Differentiation

We identify new mRNA targets for the QKI-6 RNA binding proteins using an unbiased approach. We show that AIP-1 mRNA is bound by QKI-6 within its 3′-UTR. This regulation is observed in oligodendrocytes and it is essential for oligodendrocyte process outgrowth

Vestigial Is Required during Late-Stage Muscle Differentiation in Drosophila melanogaster Embryos

The Drosophila member of the vestigial-like gene family (vestigial) is known primarily as a transcriptional activator that defines cell identity during Drosophila wing differentiation. We show that during embryo development Vestigial also has a role during specification of muscle–muscle attachments in ventral longitudinal muscles

Specification of hypothalamic neurons by dual regulation of the homeodomain protein Orthopedia

In the developing hypothalamus, a variety of neurons are generated adjacent to each other in a highly coordinated, but poorly understood process. A critical question that remains unanswered is how coordinated development of multiple neuronal types is achieved in this relatively narrow anatomical region. We focus on dopaminergic (DA) and oxytocinergic (OT) neurons as a paradigm for development of two prominent hypothalamic cell types. We report that the development of DA and OT-like neurons in the zebrafish is orchestrated by two novel pathways that regulate the expression of the homeodomain-containing protein Orthopedia (Otp), a key determinant of hypothalamic neural differentiation. Genetic analysis showed that the G-protein-coupled receptor PAC1 and the zinc finger-containing transcription factor Fezl act upstream to Otp. In vivo and in vitro experiments demonstrated that Fezl and PAC1 regulate Otp at the transcriptional and the post-transcriptional levels, respectively. Our data reveal a new genetic network controlling the specification of hypothalamic neurons in vertebrates, and places Otp as a critical determinant underlying Fezl- and PAC1-mediated differentiation