Proteomics analyses of microvesicles released by Drosophila Kc167 and S2 cells

Distinct types of vesicles are formed in eukaryotic cells that conduct a variable set of functions depending on their origin. One subtype designated circulating microvesicles (MVs) provides a novel form of intercellular communication and recent work suggested the release and uptake of morphogens in vesicles by Drosophila cells. In this study, we have examined cells of the hemocyte-like cell lines Kc167 and S2 and identified secreted vesicles in the culture supernatant. The vesicles were isolated and found to have characteristics comparable to exosomes and plasma membrane MVs released by mammalian cells. In wingless-transfected cells, the full-length protein was detected in the vesicle isolates. Proteomics analyses of the vesicles identified 269 proteins that include various orthologs of marker proteins and proteins with putative functions in vesicle formation and release. Analogous to their mammalian counterparts, the subcellular origin of the vesicular constituents of both cell lines is dominated by membrane-associated and cytosolic proteins with functions that are consistent with their localization in MVs. The analyses revealed a significant overlap of the Kc167 and S2 vesicle proteomes and confirmed a close correlation with non-mammalian and mammalian exosomes.     

Functional dissection of phosphorylation of Disheveled in Drosophila

Disheveled/Dsh proteins (Dvl in mammals) are core components of both Wnt/Wg-signaling pathways: canonical β-catenin signaling and Frizzled (Fz)-planar cell polarity (PCP) signaling. Although Dsh is a key cytoplasmic component of both Wnt/Fz-pathways, regulation of its signaling specificity is not well understood. Dsh is phosphorylated, but the functional significance of its phosphorylation remains unclear. We have systematically investigated the phosphorylation of Dsh by combining mass-spectrometry analyses, biochemical studies, and in vivo genetic methods in Drosophila. Our approaches identified multiple phospho-residues of Dsh in vivo. Our data define three novel and unexpected conclusions: (1) strikingly and in contrast to common assumptions, all conserved serines/threonines are non-essential for Dsh function in either pathway; (2) phosphorylation of conserved Tyrosine473 in the DEP domain is critical for PCP-signaling — Dsh^Y473F behaves like a PCP-specific allele; and (3) defects associated with the PCP specific dsh¹ allele, Dsh^K417M, located within a putative Protein Kinase C consensus site, are likely due to a post-translational modification requirement of Lys417, rather than phosphorylation nearby. In summary, our combined data indicate that while many Ser/Thr and Tyr residues are indeed phosphorylated in vivo, strikingly most of these phosphorylation events are not critical for Dsh function with the exception of DshY473.     

The Drosophila tumor suppressors Expanded and Merlin differentially regulate cell cycle exit, apoptosis, and Wingless signaling

Mutations that inactivate either merlin (mer) or expanded (ex) result in increased cell growth and proliferation in Drosophila. Both Mer and Ex are members of the Band 4.1 protein superfamily, and, based on analyses of mer ex double mutants, they are proposed to function together in at least a partially redundant manner upstream of the Hippo (Hpo) and Warts (Wts) proteins to regulate cell growth and division. By individually analyzing ex and mer mutant phenotypes, we have found important qualitative and quantitative differences in the ways Mer and Ex function to regulate cell proliferation and cell survival. Though both mer and ex restrict cell and tissue growth, ex clones exhibit delayed cell cycle exit in the developing eye, while mer clones do not. Conversely, loss of mer substantially compromises normal developmental apoptosis in the pupal retina, while loss of ex has only mild effects. Finally, ex has a role in regulating Wingless protein levels in the eye that is not obviously shared by either mer or hpo. Taken together, our data suggest that Mer and Ex differentially regulate multiple downstream pathways.     

Endometrial stromal cells and decidualized stromal cells: Origins,transformation and functions

Decidualization of endometrium, which is characterized by endometrial stromal cell (ESC) decidualization, vascular reconstruction, immune cell recruitment, and plentiful molecule production, is a crucial step for uterus to become receptive for embryo. When implantation takes place, ESCs surround and directly interact with embryo. Decidualized stromal cells (DSCs) are of great importance in endometrial decidualization, having a broad function in regulating immune activity and vascular remodeling of uterus. DSCs are shown to have a higher metabolic level and looser cytoskeleton than ESCs. What's the origin of ESCs and how ESCs successfully transform into DSCs had puzzled scientists in the last decades. Breakthrough had been achieved recently, and many studies had elucidated some of the characters and functions of DSCs. However, several questions still remain unclear. This paper reviews current understanding of where ESCs come from and how ESCs differentiate into DSCs, summarizes some characters and functions of DSCs, analyzes current studies and their limitations and points out research areas that need further investigation.     

Three genes control the timing, the site and the size of blastema formation in Drosophila

Regeneration is a vital process to maintain and repair tissues. Despite the importance of regeneration, the genes responsible for regenerative growth remain largely unknown. In Drosophila, imaginal disc regeneration can be induced either by fragmentation and in vivo culture or in situ by ubiquitous expression of wingless (wg/wnt1). Imaginal discs, like appendages in lower vertebrates, initiate regeneration by wound healing and proliferation at the wound site, forming a regeneration blastema. Most blastema cells maintain their disc-specific identity during regeneration; a few cells however, exhibit stem-cell like properties and switch to a different fate, in a phenomenon known as transdetermination. We identified three genes, regeneration (rgn), augmenter of liver regeneration (alr) and Matrix metalloproteinase-1 (Mmp1) expressed specifically in blastema cells during disc regeneration. Mutations in these genes affect both fragmentation- and wg-induced regeneration by either delaying, reducing or positioning the regeneration blastema. In addition to the modifications of blastema homeostasis, mutations in the three genes alter the rate of regeneration-induced transdetermination. We propose that these genes function in regenerative proliferation, growth and regulate cellular plasticity.