Loss of function of phosphatidylserine synthase causes muscle atrophy in Drosophila.

Maintenance of appropriate muscle mass is crucial for physical activity and metabolism. Aging and various pathological conditions can cause sarcopenia, a condition characterized by muscle mass decline. Although sarcopenia has been actively studied, the mechanisms underlying muscle atrophy are not well understood. Thus, we aimed to investigate the role of Phosphatidylserine synthase (Pss) in muscle development and homeostasis in Drosophila. The results showed that muscle-specific Pss knockdown decreased exercise capacity and produced sarcopenic phenotypes. In addition, it increased the apoptosis rate because of the elevated reactive oxygen species production resulting from mitochondrial dysfunction. Moreover, the autophagy rate increased due to increased FoxO activity caused by reduced Akt activity. Collectively, these findings demonstrate that enhanced apoptosis and autophagy rates resulting from muscle-specific Pss knockdown jointly contribute to sarcopenia development, highlighting the key role of the PSS pathway in muscle health.

Molecular and genetics inquiry program using Drosophila eyes absent gene.

The aim of this study was to develop molecular genetics inquiry programs using the eyes absent gene of Drosophila melanogaster. The program was composed of various molecular genetics experiments, including mutation observation, cross-breeding, searching for genetic information in web databases, gDNA extraction, and PCR. Each experiment was designed to include a reasoning process, thus aligning the program closely with the structure of authentic scientific research. This program was also developed with a modular design to provide flexibility in its implementation. The program was implemented for middle school students affiliated with a university science education institute for the gifted, and surveys indicated that students had positive experiences with the program. Our findings suggest that the program provides students with a contextual understanding of how authentic research is conducted. Finally, we suggest ways to implement the program effectively.

CG11426 gene product negatively regulates glial population size in the Drosophila eye imaginal disc.

Glial cells play essential roles in the nervous system. Although glial populations are tightly regulated, the mechanisms regulating the population size remain poorly understood. Since Drosophila glial cells are similar to the human counterparts in their functions and shapes, rendering them an excellent model system to understand the human glia biology. Lipid phosphate phosphatases (LPPs) are important for regulating bioactive lipids. In Drosophila, there are three known LPP-encoding genes: wunen, wunen-2, and lazaro. The wunens are important for germ cell migration and survival and septate junction formation during tracheal development. Lazaro is involved in phototransduction. In the present study, we characterized a novel Drosophila LPP-encoding gene, CG11426. Suppression of CG11426 increased glial cell number in the eye imaginal disc during larval development, while ectopic CG11426 expression decreased it. Both types of mutation also caused defects in axon projection to the optic lobe in larval eye-brain complexes. Moreover, CG11426 promoted apoptosis via inhibiting ERK signaling in the eye imaginal disc. Taken together, these findings demonstrated that CG11426 gene product negatively regulates ERK signaling to promote apoptosis for proper maintenance of the glial population in the developing eye disc.

Phosphatidylserine synthase plays an essential role in glia and affects development, as well as the maintenance of neuronal function.

Phosphatidylserine (PS) is an integral component of eukaryotic cell membranes and organelles. The Drosophila genome contains a single PS synthase (PSS)-encoding gene (Pss) homologous to mammalian PSSs. Flies with Pss loss-of-function alleles show a reduced life span, increased bang sensitivity, locomotor defects, and vacuolated brain, which are the signs associated with neurodegeneration. We observed defective mitochondria in mutant adult brain, as well as elevated production of reactive oxygen species, and an increase in autophagy and apoptotic cell death. Intriguingly, glial-specific knockdown or overexpression of Pss alters synaptogenesis and axonal growth in the larval stage, causes developmental arrest in pupal stages, and neurodegeneration in adults. This is not observed with pan-neuronal up- or down-regulation. These findings suggest that precisely regulated expression of Pss in glia is essential for the development and maintenance of brain function. We propose a mechanism that underlies these neurodegenerative phenotypes triggered by defective PS metabolism.

The pleiohomeotic gene is required for maintaining expression of genes functioning in ventral appendage formation in Drosophila melanogaster.

Polycomb group (PcG) proteins are negative regulators that maintain the expression of homeotic genes and affect cell proliferation. Pleiohomeotic (Pho) is a unique PcG member with a DNA-binding zinc finger motif and was proposed to recruit other PcG proteins to form a complex. The pho null mutants exhibited several mutant phenotypes such as the transformation of antennae to mesothoracic legs. We examined the effects of pho on the identification of ventral appendages and proximo-distal axis formation during postembryogenesis. In the antennal disc of the pho mutant, Antennapedia (Antp), which is a selector gene in determining leg identity, was ectopically expressed. The homothorax (hth), dachshund (dac) and Distal-less (Dll) genes involved in proximo-distal axis formation were also abnormally expressed in both the antennal and leg discs of the pho mutant. The engrailed (en) gene, which affects the formation of the anterior-posterior axis, was also misexpressed in the anterior compartment of antennal and leg discs. These mutant phenotypes were enhanced in the mutant background of Posterior sex combs (Psc) and pleiohomeotic-like (phol), which are another PcG genes. These results suggest that pho functions in maintaining expression of genes involved in the formation of ventral appendages and the proximo-distal axis.

The CNS midline cells and Egfr signaling genes are required for establishment of the RP2 motoneuron lineage in the Drosophila central nervous system.

It is well established that CNS midline cells are essential for the identity determination, division, and differentiation of neurons and glia in the Drosophila CNS. However, it is not clear whether CNS midline cells control the establishment and differentiation of the well-known RP2 motoneuron lineage. The present study showed by using several RP2 lineage markers that CNS midline cells and Egfr signaling genes are required for identity determination and formation of precursors of the RP2 motoneurons. Overexpression and ectopic expression of sim and components of the EGFR signaling pathway in the ventral neuroectoderm induced the formation of extra RP2s and their sibling cells by activating EGFR signaling. We demonstrated that CNS midline cells and Egfr signaling genes play essential roles in the establishment of the RP2 motoneuron lineage.

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.

Computational-aided identification of genes regulated by the Drosophila vnd.

Neurogenesis in Drosophila melanogaster is initiated by an ordered appearance of neuroblasts arranged in three columns (medial, intermediate, and lateral) in the neuroectoderm. In each column, specific homeodomain-containing genes are expressed. The ventral nervous system defective (vnd) regulates the fate of the cells in the medial domain of the neuroectoderm. In the present study, we identified Vnd-regulated genes through computational screening. Through further screening, we selected eight genes that were downregulated in the vnd loss-of function mutation. These included zfh1, uzip, CG7687, SytIV, stau, ase, scrt, and dpn genes. Ectopic expression of vnd, using the GAL4/UAS system, caused abnormal expression of all eight genes. Further, eight genes were coexpressed with that of vnd. Reverse-transcriptase polymerase chain reaction (RT-PCR) experiments showed an enhanced expression of uzip, CG7687, SytIV, and ase. Although the other four genes did not show an enhanced expression through RT-PCR, cytochemical and genetic evidence showed that these genes were regulated by Vnd. Taken together, the results obtained from this study indicate that expression of at least four genes, uzip, CG7687, SytIV, and ase, are regulated by Vnd.

Dpp represses eagle expression at short-range, but can repress its expression at a long-range via EGFR signal repression.

Nervous system development takes place after positional information has been established along the dorsal-ventral (D/V) axis. The initial subdivision provided by a gradient of nuclear dorsal protein is maintained by the zygotic genes expressed along the D/V axis. In this study, an investigation was conducted to determine the range of Dpp function in repressing the expression of eagle (eg) that is present in intermediate neuroblasts defective (ind) and muscle specific homeobox (msh) gene domain. eg is expressed in neuroblast (NB) 2-4, 3-3 and 6-4 of the msh domain, and NB7-3 of the ind domain at the embryonic stage 11. In decapentaplegic (dpp) loss-of-function mutant embryos, eg was ectopically expressed in the dorsal region, while in dpp gain-of-function mutants produced by sog or sca-GAL4/UAS-dpp, eg was repressed by Dpp. It is worthy of note that Dpp produced from sim;;dpp embryos showed that Dpp could function at long range. However, Dpp produced from en-GAL4/UAS-dpp or wg-GAL4/UAS-dpp primarily acted at short-range. This result demonstrated that this discrepancy seems to be due to the repression of Dpp to EGFR signaling in sim;;dpp embryos. Taken together, these results suggest that Dpp signaling works at short-range, but can function indirectly at long-range by way of repression of EGFR signaling during embryonic neurogenesis.

Temporal and spatial expression of homeotic genes is important for segment-specific neuroblast 6-4 lineage formation in Drosophila.

Different proliferation of neuroblast 6-4 (NB6-4) in the thorax and abdomen produces segmental specific expression pattern of several neuroblast marker genes. NB6-4 is divided to form four medialmost cell body glia (MM-CBG) per segment in thorax and two MM-CBG per segment in abdomen. As homeotic genes determine the identities of embryonic segments along theA/P axis, we investigated if temporal and specific expression of homeotic genes affects MM-CBG patterns in thorax and abdomen. A Ubx loss-of-function mutation was found to hardly affect MM-CBG formation, whereas abd-A and Abd-B caused the transformation of abdominal MM-CBG to their thoracic counterparts. On the other hand, gain-of-function mutants of Ubx, abd-A and Abd-B genes reduced the number of thoracic MM-CBG, indicating that thoracic MM-CBG resembled abdominal MM-CBG. However, mutations in Polycomb group (PcG) genes, which are negative transregulators of homeotic genes, did not cause the thoracic to abdominal MM-CBG pattern transformation although the number of MM-CBG in a few per-cent of embryos were partially reduced or abnormally patterned. Our results indicate that temporal and spa-tial expression of the homeotic genes is important to determine segmental-specificity of NB6-4 daughter cells along the anterior-posterior (A/P) axis.

The Drosophila pleiohomeotic mutation enhances the Polycomblike and Polycomb mutant phenotypes during embryogenesis and in the adult.

In Drosophila, the spatially restricted expression of the homeotic genes is controlled by Polycomb group (PcG) repression. PcG proteins appear to form different complexes to repress this gene expression. Although the pleiohomeotic gene (pho) shares mutational phenotypes with other PcG mutations, which demonstrates that PHO binds directly with a Polycomb (Pc)-containing complex, the genetic interactions of pho with other PcG genes have not been examined in detail. Here we investigated whether pho interacts with Polycomblike (Pcl) and Polycomb (Pc) during embryonic and adult development using developmental and genetic approaches. Pcl and Pc strongly enhanced pho phenotypes in the legs and tergite of the adult fly. Embryonic cuticle transformation was also greatly enhanced in Pcl; pho or Pc; pho double mutant embryos. The double mutant phenotypes were more severely affected by the pho maternal effect mutation than in zygotic mutant background, suggesting dosage-dependent processes. Taken together, these results provide genetic evidence of an interaction between PHO with other Polycomb group proteins at the embryonic and adult stages, and of the functioning of PHO as a component of the PcG complex.

Local inhibition of Drosophila homeobox-containing neural dorsoventral patterning genes by Dpp.

An important step in Drosophila neurogenesis is to establish the neural dorsoventral (DV) patterning. Here we describe how dpp loss-of- and gain-of-function mutation affects the homeobox-containing neural DV patterning genes expressed in the ventral neuroectoderm. Ventral nervous system defective (vnd), intermediate neuroblast defective (ind), muscle-specific homeobox (msh), and orthodenticle (otd) genes participate in development of the central nervous system and peripheral nervous system, and encode homeodomain proteins. otd and msh genes were ectopically expressed in dpp loss-of-function mutation, but vnd and ind were not affected. However, when dpp was ectopically expressed in the ventral neuroectoderm by rho-GAL4/UAS-dpp system, it caused the repression of vnd, and msh expressions in ventral and dorsal columns of the neuroectoderm, respectively, but not that of ind. The later expression pattern of otd was also restricted by Dpp. The expression pattern of msh, vnd and otd in dpp loss-of-function and gain-of-function mutation indicates that Dpp activity does not reach to the ventral midline and it works locally to establish the dorsal boundary of the ventral neuroectoderm.

The hierarchical relationship among the spitz/Egfr signaling genes in cell fate determination in the Drosophila ventral neuroectoderm.

The spitz class and Egfr signaling (spi/Egfr) genes are required for the proper establishment of cell fate in the Drosophila ventral neuroectoderm. We investigated the role of the central nervous system (CNS) midline cells, and the hierarchical relationship among the spi/Egfr genes, in this process by analyzing the spatial and temporal expression of several of the genes in selected spi/Egfr mutants. Our analysis showed that expression of all the spi/Egfr genes is severely reduced in the single-minded (sim) mutant, and ectopically induced in en-Gal4/UAS-sim embryos. This result indicates that sim acts upstream of all the other spi/Egfr genes. The CNS midline cells regulate rhomboid (rho) expression in the ventral neuroectoderm and activate the EGFR signaling pathway. We also found that argos (aos) and orthodenticle (otd) act downstream of pointed (pnt), and that aos represses expression of otd in the lateral neuroectoderm to establish differential cell fates in the ventral neuroectoderm. Our findings suggest the following hierarchical relationship among the spi/Egfr genes: [see text].

Expression of a set of glial cell-specific markers in the Drosophila embryonic central nervous system.

The types of glia in the central nervous system (CNS) of the Drosophila embryo include longitudinal glia (LG), cell body glia (CBG), and peripheral glia (PG). Transcription factors, such as glial cell missing and reverse polarity, are well-established general glial cell markers. Only a few glial cell-specific markers have been identified in the Drosophila embryonic CNS, thus far. In the present study, we employed the glial cell-specific markers for LG (vir-1/CG5453 and CG31235), CBG (fabp/CG6783 and CG11902), and PG (CG2310 and moody/CG4322), and comprehensively analyzed their expression patterns, during the embryonic CNS development. Our study validated the specificity of a set of glial markers, and further revealed their spatio-temporal expression patterns, which will aid in the understanding of the developmental lineage, and investigating their role in the development and homeostasis of the Drosophila CNS in vivo.

The pleiohomeotic functions as a negative regulator of Drosophila even-skipped gene during embryogenesis.

Polycomb group (PcG) proteins maintain the spatial expression patterns of genes that are involved in cell-fate specification along the anterior-posterior (A/P) axis. This repression requires cis-acting silencers, which are called PcG response elements (PREs). One of the PcG proteins, Pleiohomeotic (Pho), which has a zinc finger DNA binding protein, plays a critical role in recruiting other PcG proteins to bind to PREs. In this study, we characterized the effects of a pho mutation on embryonic segmentation. pho maternal mutant embryos showed various segmental defects including pair-rule gene mutant patterns. Our results indicated that engrailed and even-skipped genes were misexpressed in pho mutant embryos, which caused embryonic segment defects.

Drosophila castor is regulated negatively by the Ubx and abdA genes, but positively by the AbdB gene.

The ventral nerve cord (VNC) of Drosophila exhibits significant segmental-specific characteristics during embryonic development. Homeotic genes are expressed over long periods of time and confer identity to the different segments. castor (cas) is one of the genes which are expressed in neuroblasts along the VNC. However, at late embryonic stages, cas transcripts are found only in head and thoracic segments and terminal abdominal segments, while Cas protein lasts longer in all segments. In this study, we investigated the regulation of temporal and spatial expression of cas by the bithorax complex genes. In the loss-of-function mutants of Ultrabithorax (Ubx) and abdominal-A (abdA), cas transcripts were ectopically expressed in abdominal segments at late embryonic stage. However, unlike in Ubx and abdA mutants, in Abdominal-B (AbdB) loss-of-function mutant embryos, cas disappeared in the terminal region. Ectopic Ubx and abdA suppressed cas expression, but ectopic AbdB activated cas expression in most abdominal segments. Moreover, cas was co-expressed in the cells in which AbdB was normally expressed, and overexpressed in the ectopically expressed AbdB embryos. These results suggest that the expression of cas is segment-specifically regulated negatively by Ubx and abdA genes, but positively by the AbdB gene.

CNS midline cells are required for establishment and differentiation of Drosophila MP2 interneurons.

The Drosophila CNS develops from the ventral neuroectoderm (VNE) on both sides of the midline along the dorsoventral axis. During early neurogenesis, three homeodomain and Egfr signaling genes are required for the dorsoventral patterning of the VNE. However, the roles of CNS midline cells in patterning of the specific neural lineages are not well understood. Their roles in identity determination and differentiation of the well-established MP2 lineage were studied using several molecular markers. We showed that these cells are essential for identity determination of the MP2 lineage that originates from the VNE. The midline cells and the Egfr signaling genes were also required for the proper maintenance of MP2 and the correct formation of MP2 axonal pathways. Overexpression of sim in the midline cells activated ectopic expression of MP2 markers in the VNE. This analysis suggests that CNS midline cells and Egfr signaling genes play essential roles in the proper establishment and differentiation of the MP2 lineage.

CNS midline cells influence the division and survival of lateral glia in the Drosophila nervous system.

Central nervous system (CNS) midline cells are essential for identity determination and differentiation of neurons in the Drosophila nervous system. It is not clear, however, whether CNS midline cells are also involved in the development of lateral glial cells. The roles of CNS midline cells in lateral glia development were elucidated using general markers for lateral glia, such as glial cell missing and reverse polarity, and specific enhancer trap lines labeling the longitudinal, A, B, medial cell body, peripheral, and exit glia. We found that CNS midline cells were necessary for the proper expression of glial cell missing, reverse polarity, and other lateral glia markers only during the later stages of development, suggesting that they are not required for initial identity determination. Instead, CNS midline cells appear to be necessary for proper division and survival of lateral glia. CNS midline cells were also required for proper positioning of three exit glia at the junction of segmental and intersegmental nerves, as well as some peripheral glia along motor and sensory axon pathways. This study demonstrated that CNS midline cells are extrinsically required for the proper division, migration, and survival of various classes of lateral glia from the ventral neuroectoderm.

CNS midline cells contribute to maintenance of the initial dorsoventral patterning of the Drosophila ventral neuroectoderm.

Dorsoventral patterning of the Drosophila ventral neuroectoderm is established by the expression of three evolutionarily conserved homeodomain genes: ventral nervous system defective (vnd), intermediate neuroblasts defective (ind), and muscle segment homeobox (msh) in the medial, intermediate, and lateral columns of the ventral neuroectoderm, respectively. It was not clear whether extrinsic factor(s) from the CNS midline cells influence the initial dorsoventral patterning by controlling the expression of the dorsoventral patterning genes. We show here that the CNS midline cells, specified by single-minded (sim), are essential for maintaining expression of the dorsoventral patterning genes. Ectopic expression of sim in the ventral neuroectoderm during the blastoderm stage repressed expression of the three homeodomain genes in the ventral neuroectoderm. This indicates that the identity of the CNS midline cells is established by a series of repressions of the three homeodomain genes in the ventral neuroectoderm. Ectopic expression of sim in the ventral neuroectoderm during initial neurogenesis induced ectopic ind expression in the medial column in addition to that in the intermediate column via EGFR signaling between the ventral neuroectoderm and midline cells. In contrast, it repressed the expression of vnd and msh in the medial and lateral columns, respectively. Our findings demonstrate that the CNS midline cells provide extrinsic positional information via EGFR signaling that maintains the initial subdivision of the ventral neuroectoderm into three dorsoventral columns during initial neurogenesis.