The deubiquitinase emperor's thumb is a regulator of apoptosis in Drosophila

We have characterized the gene emperor's thumb (et) and showed that it is required for the regulation of apoptosis in Drosophila. Loss-of-function mutations in et result in apoptosis associated with a decrease in the concentration of DIAP1. Overexpression of one form of et inhibits apoptosis, consistent with et having an anti-apoptotic function; however, overexpression of a second form of et induces apoptosis, indicating that the two forms of et may have competing functions. et encodes a protein deubiquitinase, suggesting it regulates apoptosis by controlling the stability of apoptotic regulatory proteins.     

Myoblast fusion in Drosophila

The body wall musculature of a Drosophila larva is composed of an intricate pattern of 30 segmentally repeated muscle fibers in each abdominal hemisegment. Each muscle fiber has unique spatial and behavioral characteristics that include its location, orientation, epidermal attachment, size and pattern of innervation. Many, if not all, of these properties are dictated by founder cells, which determine the muscle pattern and seed the fusion process. Myofibers are then derived from fusion between a specific founder cell and several fusion competent myoblasts (FCMs) fusing with as few as 3-5 FCMs in the small muscles on the most ventral side of the embryo and as many as 30 FCMs in the larger muscles on the dorsal side of the embryo. The focus of the present review is the formation of the larval muscles in the developing embryo, summarizing the major issues and players in this process. We have attempted to emphasize experimentally-validated details of the mechanism of myoblast fusion and distinguish these from the theoretically possible details that have not yet been confirmed experimentally. We also direct the interested reader to other recent reviews that discuss myoblast fusion in Drosophila, each with their own perspective on the process [1], [2], [3] and [4]. With apologies, we use gene nomenclature as specified by Flybase (http://flybase.org) but provide Table 1 with alternative names and references.     

Sex-specific repression of dachshund is required for Drosophila sex comb development

The origin of new morphological structures requires the establishment of new genetic regulatory circuits to control their development, from initial specification to terminal differentiation. The upstream regulatory genes are usually the first to be identified, while the mechanisms that translate novel regulatory information into phenotypic diversity often remain obscure. In particular, elaborate sex-specific structures that have evolved in many animal lineages are inevitably controlled by sex-determining genes, but the genetic basis of sexually dimorphic cell differentiation is rarely understood. In this report, we examine the role of dachshund (dac), a gene with a deeply conserved function in sensory organ and appendage development, in the sex comb, a recently evolved male-specific structure found in some Drosophila species. We show that dac acts during metamorphosis to restrict sex comb development to the appropriate leg region. Localized repression of dac by the sex determination pathway is necessary for male-specific morphogenesis of sex comb bristles. This pupal function of dac is separate from its earlier role in leg patterning, and Dac at this stage is not dependent on the pupal expression of Distalless (Dll), the main regulator of dac during the larval period. Dll acts in the epithelial cells surrounding the sex comb during pupal development to promote sex comb rotation, a complex cellular process driven by coordinated cell rearrangement. Our results show that genes with well-conserved developmental functions can be re-used at later stages in development to regulate more recently evolved traits. This mode of gene co-option may be an important driver of evolutionary innovations.     

Syntrophin-2 is required for eye development in Drosophila

Syntrophins are components of the dystrophin glycoprotein complex (DGC), which is encoded by causative genes of muscular dystrophies. The DGC is thought to play roles not only in linking the actin cytoskeleton to the extracellular matrix, providing stability to the cell membrane, but also in signal transduction. Because of their binding to a variety of different molecules, it has been suggested that syntrophins are adaptor proteins recruiting signaling proteins to membranes and the DGC. However, critical roles in vivo remain elusive. Drosophila Syntrophin-2 (Syn2) is an orthologue of human γ1/γ2-syntrophins. Western immunoblot analysis here showed Syn2 to be expressed throughout development, with especially high levels in the adult head. Morphological aberrations were observed in Syn2 knockdown adult flies, with lack of retinal elongation and malformation of rhabdomeres. Furthermore, Syn2 knockdown flies exhibited excessive apoptosis in third instar larvae and alterations in the actin localization in the pupal retinae. Genetic crosses with a collection of Drosophila deficiency stocks allowed us to identify seven genomic regions, deletions of which caused enhancement of the rough eye phenotype induced by Syn2 knockdown. This information should facilitate identification of Syn2 regulators in Drosophila and clarification of roles of Syn2 in eye development.     

Ectopic Repo suppresses expression of castor gene in Drosophila central nervous system

The ventral nerve cord (VNC) of the Drosophila embryo is derived from neuroblasts (NBs). NBs divide in a stem cell lineage to generate a series of ganglion mother cells (GMCs), each of which divides once to produce a pair of neurons or glial cells. One of the NB genes, castor (cas), is expressed in a subset of NBs and has never been identified in neurons and the peripheral nervous system; cas plays a role in axonogenesis. But its limited expression along the dorsal-ventral axis within the central nervous system has not been investigated yet. In the present study, we examined the expression patterns of both genes using confocal microscopy to determine the effects of repo mutation on cas expression. Cas was mainly expressed in layers different from repo-expressed layers during early embryogenesis: repo was expressed mostly from deep to mid layers, while cas, from mid to superficial layers. Loss-of-function of repo did not result in an ectopic expression of cas, but rather, a scattering of cas-expressing cells. However, repo gain-of-function mutation caused repression of cas. In addition, repo-expressing cells seemed to block the migration of cas-expressing cells.     

On the roles of Notch, Delta, kuzbanian, and inscuteable during the development of Drosophila embryonic neuroblast lineages

The generation of cellular diversity in the nervous system involves the mechanism of asymmetric cell division. Besides an array of molecules, including the Par protein cassette, a heterotrimeric G protein signalling complex, Inscuteable plays a major role in controlling asymmetric cell division, which ultimately leads to differential activation of the Notch signalling pathway and correct specification of the two daughter cells. In this context, Notch is required to be active in one sibling and inactive in the other. Here, we investigated the requirement of genes previously known to play key roles in sibling cell fate specification such as members of the Notch signalling pathway, e.g., Notch (N), Delta (Dl), and kuzbanian (kuz) and a crucial regulator of asymmetric cell division, inscuteable (insc) throughout lineage progression of 4 neuroblasts (NB1-1, MP2, NB4-2, and NB7-1). Notch-mediated cell fate specification defects were cell-autonomous and were observed in all neuroblast lineages even in cells born from late ganglion mother cells (GMC) within the lineages. We also show that Dl functions non-autonomously during NB lineage progression and clonal cells do not require Dl from within the clone. This suggests that within a NB lineage Dl is dispensable for sibling cell fate specification. Furthermore, we provide evidence that kuz is involved in sibling cell fate specification in the central nervous system. It is cell-autonomously required in the same postmitotic cells which also depend on Notch function. This indicates that KUZ is required to facilitate a functional Notch signal in the Notch-dependent cell for correct cell fate specification. Finally, we show that three neuroblast lineages (NB1-1, NB4-2, and NB7-1) require insc function for sibling cell fate specification in cells born from early GMCs whereas insc is not required in cells born from later GMCs of the same lineages. Thus, there is differential requirement for insc for cell fate specification depending on the stage of lineage progression of NBs.     

The Him gene inhibits the development of Drosophila flight muscles during metamorphosis

During Drosophila metamorphosis some larval tissues escape the general histolysis and are remodelled to form adult tissues. One example is the dorso-longitudinal muscles (DLMs) of the indirect flight musculature. They are formed by an intriguing process in which residual larval oblique muscles (LOMs) split and fuse with imaginal myoblasts associated with the wing disc. These myoblasts arise in the embryo, but remain undifferentiated throughout embryogenesis and larval life, and thus share characteristics with mammalian satellite cells. However, the mechanisms that maintain the Drosophila myoblasts in an undifferentiated state until needed for LOM remodelling are not understood. Here we show that the Him gene is expressed in these myoblasts, but is undetectable in developing DLM fibres. Consistent with this, we found that Him could inhibit DLM development: it inhibited LOM splitting and resulted in fibre degeneration. We then uncovered a balance between mef2, a positive factor required for proper DLM development, and the inhibitory action of Him. Mef2 suppressed the inhibitory effect of Him on DLM development, while Him could suppress the premature myosin expression induced by mef2 in myoblasts. Furthermore, either decreased Him function or increased mef2 function disrupted DLM development. These findings, together with the co-expression of Him and Mef2 in myoblasts, indicate that Him may antagonise mef2 function during normal DLM development and that Him participates in a balance of signals that controls adult myoblast differentiation and remodelling of these muscle fibres. Lastly, we provide evidence for a link between Notch function and Him and mef2 in this balance.     

Thermal preference in Drosophila

Environmental temperature strongly affects physiology of ectotherms. Small ectotherms, like Drosophila, cannot endogenously regulate body temperature so must rely on behavior to maintain body temperature within a physiologically permissive range. Here we review what is known about Drosophila thermal preference. Work on thermal behavior in this group is particularly exciting because it provides the opportunity to connect genes to neuromolecular mechanisms to behavior to fitness in the wild.     

A novel Drosophila Girdin-like protein is involved in Akt pathway control of cell size

The Akt signaling pathway is well known to regulate cell proliferation and growth. Girdin, a novel substrate of Akt, plays a crucial role in organization of the actin cytoskeleton and cell motility under the control of Akt. We here identified a novel Girdin-like protein in Drosophila (dGirdin), which has two isoforms, dGirdin PA and dGirdin PB. dGirdin shows high homology with human Girdin in the N-terminal and coiled-coil domains, while diverging at the C-terminal domain. On establishment of transgenic fly lines, featuring knockdown or overexpression of dGirdin in vivo, overexpression in the wing disc cells induced ectopic apoptosis, implying a role in directing apoptosis. Knockdown of dGirdin in the Drosophila wing imaginal disc cells resulted in reduction of cell size. Furthermore, this was enhanced by half reduction of the Akt gene dose, suggesting that Akt positively regulates dGirdin. In the wing disc, cells in which dGirdin was knocked down exhibited disruption of actin filaments. From these in vivo analyses, we conclude that dGirdin is required for actin organization and regulation of appropriate cell size under control of the Akt signaling pathway.     

Regulation of apoptosis of rbf mutant cells during Drosophila development

Inactivation of the retinoblastoma gene Rb leads to defects in cell proliferation, differentiation, or apoptosis, depending on specific cell or tissue types. To gain insights into the genes that can modulate the consequences of Rb inactivation, we carried out a genetic screen in Drosophila to identify mutations that affected apoptosis induced by inactivation of the Retinoblastoma-family protein (rbf) and identified a mutation that blocked apoptosis induced by rbf. We found this mutation to be a new allele of head involution defective (hid) and showed that hid expression is deregulated in rbf mutant cells in larval imaginal discs. We identified an enhancer that regulates hid expression in response to developmental cues as well as to radiation and demonstrated that this hid enhancer is directly repressed by RBF through an E2F binding site. These observations indicate that apoptosis of rbf mutant cells is mediated by an upregulation of hid. Finally, we showed that bantam, a miRNA that regulates hid translation, is expressed in the interommatidial cells in the larval eye discs and modulates the survival of rbf mutant cells.     

Behavioral dissection of Drosophila larval phototaxis

A behavior generally comprises multiple processes. Analyzing these processes helps to reveal more characteristics of the behavior. In this report, light/dark choice-based Drosophila larval phototaxis is analyzed with a simplistic mathematical model to reveal a fast phase and a slow phase response that are involved. Larvae of the strain w¹¹¹⁸, which is photophobic in phototaxis tests, prefer darkness to light in an immediate light/dark boundary passing test and demonstrate a significant reduction in motility in the dark condition during phototaxis tests. For tim⁰¹ larvae, which show neutral performance in phototaxis tests, larvae unexpectedly prefer light to darkness in the immediate light/dark boundary passing test and demonstrate no significant motility alteration in the dark condition. It is proposed that Drosophila larval phototaxis is determined by a fast phase immediate light/dark choice and an independent slow phase light/dark-induced motility alteration that follows.     

A genetic screen in Drosophila for regulators of human prostate cancer progression

To uncover the mechanism by which human prostate cancer progresses, we performed a genetic screen for regulators of human prostate cancer progression using the Drosophila accessory gland, a functional homolog of the mammalian prostate. Cell growth and migration of secondary cells in the adult male accessory gland were found to be regulated by paired, N-cadherin, and E-cadherin, which are Drosophila homologues of regulators of human prostate cancer progression. Using this screening system, we also identified three genes that promoted growth and migration of secondary cells in the accessory gland. The human homologues of these candidate genes – MRGBP, CNPY2, and MEP1A – were found to be expressed in human prostate cancer model cells and to promote replication and invasiveness in these cells. These findings suggest that the development of the Drosophila accessory gland and human prostate cancer cell growth and invasion are partly regulated through a common mechanism. The screening system using the Drosophila accessory gland can be a useful tool for uncovering the mechanisms of human prostate cancer progression.     

Hedgehog does not guide migrating Drosophila germ cells

In many species, the germ cells, precursors of sperm and egg, migrate during embryogenesis. The signals that regulate this migration are thus essential for fertility. In flies, lipid signals have been shown to affect germ cell guidance. In particular, the synthesis of geranylgeranyl pyrophosphate through the 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (Hmgcr) pathway is critical for attracting germ cells to their target tissue. In a genetic analysis of signaling pathways known to affect cell migration of other migratory cells, we failed to find a role for the Hedgehog (Hh) pathway in germ cell migration. However, previous reports had implicated Hh as a germ cell attractant in flies and suggested that Hh signaling is enhanced through the action of the Hmgcr pathway. We therefore repeated several critical experiments and carried out further experiments to test specifically whether Hh is a germ cell attractant in flies. In contrast to previously reported findings and consistent with findings in zebrafish our data do not support the notion that Hh has a direct role in the guidance of migrating germ cells in flies.     

Drosophila Fragile X Protein controls cellular proliferation by regulating cbl levels in the ovary

FMRP is an RNA binding protein linked to the most common form of inherited mental retardation, Fragile X syndrome (FraX). In addition to severe cognitive deficits, FraX etiology includes postpubescent macroorchidism, which is thought to result from overproliferation. Using a Drosophila FraX model, we show that FMRP controls germline proliferation during oogenesis. dFmr1 null ovaries contain egg chambers with both fewer and supranumerary germ cells. The mutant germaria contain a significantly increased number of cyclin E and PhosphoHistone H3 positive cells, suggesting that loss of FMRP leads to defects in cell cycle progression. BrdU incorporation and flow cytometry data suggest that, in addition to proliferation, germline endoreplication and ploidy are also affected by the loss of FMRP during ovary development. Here we report that FMRP controls the levels of cbl mRNA in the ovary and that reducing cbl gene dosage by half rescues the dFmr1 oogenesis phenotypes. These data support a model whereby FMRP controls germline proliferation by regulating the expression of cbl in the developing ovary.