Deficiency screen identifies a novel role for beta 2 tubulin in salivary gland and myoblast migration in the Drosophila embryo

Regulators of cell movement during development and regeneration in Drosophila

Cell migration is a fundamental cell biological process essential both for normal development and for tissue regeneration after damage. Cells can migrate individually or as a collective. To better understand the genetic requirements for collective migration, we expressed RNA interference (RNAi) against 30 genes in the Drosophila embryonic salivary gland cells that are known to migrate collectively. The genes were selected based on their effect on cell and membrane morphology, cytoskeleton and cell adhesion in cell culture-based screens or in Drosophila tissues other than salivary glands. Of these, eight disrupted salivary gland migration, targeting: Rac2, Rab35 and Rab40 GTPases, MAP kinase-activated kinase-2 (MAPk-AK2), RdgA diacylglycerol kinase, Cdk9, the PDSW subunit of NADH dehydrogenase (ND-PDSW) and actin regulator Enabled (Ena). The same RNAi lines were used to determine their effect during regeneration of X-ray-damaged larval wing discs. Cells translocate during this process, but it remained unknown whether they do so by directed cell divisions, by cell migration or both. We found that RNAi targeting Rac2, MAPk-AK2 and RdgA disrupted cell translocation during wing disc regeneration, but RNAi against Ena and ND-PDSW had little effect. We conclude that, in Drosophila, cell movements in development and regeneration have common as well as distinct genetic requirements.

Control of seminal fluid protein expression via regulatory hubs in Drosophila melanogaster

Highly precise, yet flexible and responsive coordination of expression across groups of genes underpins the integrity of many vital functions. However, our understanding of gene regulatory networks (GRNs) is often hampered by the lack of experimentally tractable systems, by significant computational challenges derived from the large number of genes involved or from difficulties in the accurate identification and characterization of gene interactions. Here we used a tractable experimental system in which to study GRNs: the genes encoding the seminal fluid proteins that are transferred along with sperm (the 'transferome') in Drosophila melanogaster fruit flies. The products of transferome genes are core determinants of reproductive success and, to date, only transcription factors have been implicated in the modulation of their expression. Hence, as yet, we know nothing about the post-transcriptional mechanisms underlying the tight, responsive and precise regulation of this important gene set. We investigated this omission in the current study. We first used bioinformatics to identify potential regulatory motifs that linked the transferome genes in a putative interaction network. This predicted the presence of putative microRNA (miRNA) 'hubs'. We then tested this prediction, that post-transcriptional regulation is important for the control of transferome genes, by knocking down miRNA expression in adult males. This abolished the ability of males to respond adaptively to the threat of sexual competition, indicating a regulatory role for miRNAs in the regulation of transferome function. Further bioinformatics analysis then identified candidate miRNAs as putative regulatory hubs and evidence for variation in the strength of miRNA regulation across the transferome gene set. The results revealed regulatory mechanisms that can underpin robust, precise and flexible regulation of multiple fitness-related genes. They also help to explain how males can adaptively modulate ejaculate composition.

Identification of the metastasis potential and its associated genes in melanoma multinucleated giant cells using the PHA-ECM830 fusion method

Malignant melanoma causes skin cancer with high rates of mortality. Multinucleated giant cells (MGCs) are frequently observed in tumor pathological analysis, especially in metastasized sites, and are related to poor prognosis. However, the role of MGCs in melanoma development and metastasis is currently unknown. In the present study, we obtained melanoma MGCs (M-MGCs) in vitro using the modified phytohaemagglutinin (PHA)-ECM830 electronic fusion method (fusion efficiency was significantly enhanced by adding PHA to agglutinate cells before electronic fusion). We found that M-MGCs showed decreased proliferation potential but increased pulmonary metastasis ability relative to the parental B16-F10 cells. Microarray and bioinformatics analysis showed that β-tubulin gene group was significantly upregulated in MMGCs. A member of this gene group, TUBB2B, exhibited significantly enhanced expression, indicating that it may play an important role in melanoma metastasis. Our results provide novel insights into the properties of melanoma and they could contribute towards the design of new strategies for rapid diagnosis and treatment of this cancer.

Drosophila KASH-domain protein Klarsicht regulates microtubule stability and integrin receptor localization during collective cell migration

During collective migration of the Drosophila embryonic salivary gland, cells rearrange to form a tube of a distinct shape and size. Here, we report a novel role for the Drosophila Klarsicht-Anc-Syne Homology (KASH) domain protein Klarsicht (Klar) in the regulation of microtubule (MT) stability and integrin receptor localization during salivary gland migration. In wild-type salivary glands, MTs became progressively stabilized as gland migration progressed. In embryos specifically lacking the KASH domain containing isoforms of Klar, salivary gland cells failed to rearrange and migrate, and these defects were accompanied by decreased MT stability and altered integrin receptor localization. In muscles and photoreceptors, KASH isoforms of Klar work together with Klaroid (Koi), a SUN domain protein, to position nuclei; however, loss of Koi had no effect on salivary gland migration, suggesting that Klar controls gland migration through novel interactors. The disrupted cell rearrangement and integrin localization observed in klar mutants could be mimicked by overexpressing Spastin (Spas), a MT severing protein, in otherwise wild-type salivary glands. In turn, promoting MT stability by reducing spas gene dosage in klar mutant embryos rescued the integrin localization, cell rearrangement and gland migration defects. Klar genetically interacts with the Rho1 small GTPase in salivary gland migration and is required for the subcellular localization of Rho1. We also show that Klar binds tubulin directly in vitro. Our studies provide the first evidence that a KASH-domain protein regulates the MT cytoskeleton and integrin localization during collective cell migration.

Receptor guanylyl cyclase Gyc76C is required for invagination, collective migration and lumen shape in the Drosophila embryonic salivary gland

The Drosophila embryonic salivary gland is formed by the invagination and collective migration of cells. Here, we report on a novel developmental role for receptor-type guanylyl cyclase at 76C, Gyc76C, in morphogenesis of the salivary gland. We demonstrate that Gyc76C and downstream cGMP-dependent protein kinase 1 (DG1) function in the gland and surrounding mesoderm to control invagination, collective migration and lumen shape. Loss of gyc76C resulted in glands that failed to invaginate, complete posterior migration and had branched lumens. Salivary gland migration defects of gyc76C mutant embryos were rescued by expression of wild-type gyc76C specifically in the gland or surrounding mesoderm, whereas invagination defects were rescued primarily by expression in the gland. In migrating salivary glands of gyc76C mutant embryos, integrin subunits localized normally to gland-mesoderm contact sites but talin localization in the surrounding circular visceral mesoderm and fat body was altered. The extracellular matrix protein, laminin, also failed to accumulate around the migrating salivary gland of gyc76C mutant embryos, and gyc76C and laminin genetically interacted in gland migration. Our studies suggest that gyc76C controls salivary gland invagination, collective migration and lumen shape, in part by regulating the localization of talin and the laminin matrix.

Receptor-type guanylyl cyclase Gyc76C is required for development of the Drosophila embryonic somatic muscle

Guanylyl cyclases mediate a number of physiological processes, including smooth muscle function and axonal guidance. Here, we report a novel role for Drosophila receptor-type guanylyl cyclase at 76C, Gyc76C, in development of the embryonic somatic muscle. In embryos lacking function of Gyc76C or the downstream cGMP-dependent protein kinase (cGK), DG1, patterning of the somatic body wall muscles was abnormal with ventral and lateral muscle groups showing the most severe defects. In contrast, specification and elongation of the dorsal oblique and dorsal acute muscles of gyc76C mutant embryos was normal, and instead, these muscles showed defects in proper formation of the myotendinous junctions (MTJs). During MTJ formation in gyc76C and pkg21D mutant embryos, the βPS integrin subunit failed to localize to the MTJs and instead was found in discrete puncta within the myotubes. Tissue-specific rescue experiments showed that gyc76C function is required in the muscle for proper patterning and βPS integrin localization at the MTJ. These studies provide the first evidence for a requirement for Gyc76C and DG1 in Drosophila somatic muscle development, and suggest a role in transport and/or retention of integrin receptor subunits at the developing MTJs.