Multiple isoforms of the Activin-like receptor baboon differentially regulate proliferation and conversion behaviors of neuroblasts and neuroepithelial cells in the Drosophila larval brain.

In Drosophila coordinated proliferation of two neural stem cells, neuroblasts (NB) and neuroepithelial (NE) cells, is pivotal for proper larval brain growth that ultimately determines the final size and performance of an adult brain. The larval brain growth displays two phases based on behaviors of NB and NEs: the first one in early larval stages, influenced by nutritional status and the second one in the last larval stage, promoted by ecdysone signaling after critical weight checkpoint. Mutations of the baboon (babo) gene that produces three isoforms (BaboA-C), all acting as type-I receptors of Activin-type transforming growth factor ß (TGF-ß) signaling, cause a small brain phenotype due to severely reduced proliferation of the neural stem cells. In this study we show that loss of babo function severely affects proliferation of NBs and NEs as well as conversion of NEs from both phases. By analyzing babo-null and newly generated isoform-specific mutants by CRISPR mutagenesis as well as isoform-specific RNAi knockdowns in a cell- and stage-specific manner, our data support differential contributions of the isoforms for these cellular events with BaboA playing the major role. Stage-specific expression of EcR-B1 in the brain is also regulated primarily by BaboA along with function of the other isoforms. Blocking EcR function in both neural stem cells results in a small brain phenotype that is more severe than baboA-knockdown alone. In summary, our study proposes that the Babo-mediated signaling promotes proper behaviors of the neural stem cells in both phases and achieves this by acting upstream of EcR-B1 expression in the second phase.

Biogenesis of circular RNAs in vitro and in vivo from the Drosophila Nk2.1 / scarecrow gene.

scarecrow ( scro ) encodes a fly homolog of mammalian Nkx2.1 that is vital for early fly development as well as for optic lobe development. Interestingly, scro was reported to produce a circular RNA (circRNA). In this study, we identified 12 different scro circRNAs, which are either mono- or multi-exonic forms. The most abundant forms are circE2 carrying the second exon only and bi-exonic circE3-E4. Levels of circE2 show an age-dependent increase in adult heads, supporting a general trend of high accumulation of circRNAs in aged fly brains. Aligning sequences of introns flanking exons uncovered two pairs of intronic complementary sequences (ICSs); one pair residing in introns 1 and 2 and the other in introns 2 and 4. The first pair was demonstrated to be essential for the circE2 production in cell-based assays; furthermore, deletion of the region including potential ICS components in the intron-2 reduced in vivo production of circE2 and circE3-E4 by 80%, indicating them to be essential for the biogenesis of these isoforms. Besides the ICS, the intron regions immediately abutting exons seemed to be responsible for a basal level of circRNA formation. Moreover, the replacement of scro -ICS with those derived from laccase2 was comparably effective in scro -circRNA production, buttressing the importance of the hairpin-loop structure formed by ICS for the biogenesis of circRNA. Lastly, overexpressed scro affected outcomes of both linear and circular RNAs from the endogenous scro locus, suggesting that Scro plays a direct or indirect role in regulating expression levels of either or both forms.

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.

In vivo characterization of the maturation steps of a pigment dispersing factor neuropeptide precursor in the Drosophila circadian pacemaker neurons.

Pigment dispersing factor (PDF) is a key signaling molecule coordinating the neuronal network associated with the circadian rhythms in Drosophila. The precursor (proPDF) of the mature PDF (mPDF) consists of 2 motifs, a larger PDF-associated peptide (PAP) and PDF. Through cleavage and amidation, the proPDF is predicted to produce cleaved-PAP (cPAP) and mPDF. To delve into the in vivo mechanisms underlying proPDF maturation, we generated various mutations that eliminate putative processing sites and then analyzed the effect of each mutation on the production of cPAP and mPDF by 4 different antibodies in both ectopic and endogenous conditions. We also assessed the knockdown effects of processing enzymes on the proPDF maturation. At the functional level, circadian phenotypes were measured for all mutants and knockdown lines. As results, we confirm the roles of key enzymes and their target residues: Amontillado (Amon) for the cleavage at the consensus dibasic KR site, Silver (Svr) for the removal of C-terminal basic residues from the intermediates, PAP-KR and PDF-GK, derived from proPDF, and PHM (peptidylglycine-α-hydroxylating monooxygenase) for the amidation of PDF. Our results suggest that the C-terminal amidation occurs independently of proPDF cleavage. Moreover, the PAP domain is important for the proPDF trafficking into the secretory vesicles and a close association between cPAP and mPDF following cleavage seems required for their stability within the vesicles. These studies highlight the biological significance of individual processing steps and the roles of the PAP for the stability and function of mPDF which is essential for the circadian clockworks.

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.

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.

Programmed cell death reshapes the central nervous system during metamorphosis in insects.

Metamorphosis is fascinating and dramatic stage of postembryonic development in insects [1]. The most prominent metamorphic changes seen in holometabolous insects involve destruction of most larval structures and concomitant generation of adult ones. Such diverse cellular events are orchestrated by ecdysone. The central nervous system (CNS) is also extensively remodeled to process new sensory inputs; to coordinate new types of locomotion; and to perform higher-order decision making [2]. Programmed cell death (PCD) is an integral part of the metamorphic development. It eliminates obsolete larval tissues and extra cells that are generated from the morphogenesis of adult tissues. In the CNS, PCD of selected neurons and glial cells as well as reshaping of persistent larval cells are essential for establishing the adult CNS. In this review, we summarize the ecdysone signaling, and then molecular and cellular events associated with PCD primarily in the metamorphosing CNS of Drosophila melanogaster.

Knock-in mutations of scarecrow, a Drosophila homolog of mammalian Nkx2.1, reveal a novel function required for development of the optic lobe in Drosophila melanogaster.

scarecrow (scro) gene encodes a Drosophila homolog of mammalian Nkx2.1 that belongs to an evolutionally conserved NK2 family. Nkx2.1 has been well known for its role in the development of hypothalamus, lung, thyroid gland, and brain. However, little is known about biological roles of scro. To understand scro functions, we generated two types of knock-in mutant alleles, substituting part of either exon-2 or exon-3 for EGFP (or Gal4) by employing the CRISPR/Cas9 genome editing tool. Using these mutations, we characterized spatio-temporal expression patterns of the scro gene and its mutant phenotypes. Homozygous knock-in mutants are lethal during embryonic and early larval development. In developing embryos, scro is exclusively expressed in the pharyngeal primordia and numerous neural clusters in the central nervous system (CNS). In postembryonic stages, the most prominent scro expression is detected in the larval and adult optic lobes, suggesting that scro plays a role for the development and/or function of this tissue type. Notch signaling is the earliest factor known to act for the development of the optic lobe. scro mutants lacked mitotic cells and Delta expression in the optic anlagen, and showed altered expression of several proneural and neurogenic genes including Delta and Notch. Furthermore, scro mutants showed grossly deformed neuroepithelial (NE) cells in the developing optic lobe and severely malformed adult optic lobes, the phenotypes of which are shown in Notch or Delta mutants, suggesting scro acting epistatic to the Notch signaling. From these data together, we propose that scro plays an essential role for the development of the optic lobe, possibly acting as a regional specification factor.

A Homeobox Transcription Factor Scarecrow (SCRO) Negatively Regulates Pdf Neuropeptide Expression through Binding an Identified cis-Acting Element in Drosophila melanogaster.

In Drosophila, transcriptional feedback loops contribute to intracellular timekeeping mechanisms responsible for daily rhythms. Pigment-dispersing factor (PDF) is the major neuropeptide produced by latero-ventral neurons (LNvs) that function as a central pacemaker for circadian locomotor activity rhythms. PDF synchronizes other clock neurons thereby playing an essential role in the maintenance and coordination of circadian locomotor rhythms. However, the underlying molecular mechanism of the LNvs-specific Pdf expression is not well understood. Here, using Pdf promoter-bashing experiment, we identified a cis-acting Pdf regulatory element (PRE) that is sufficient for driving Pdf expression in the LNvs. We have also identified a homeobox transcription factor, scarecrow (SCRO), as a direct binding factor to PRE. Furthermore, transgenic expression of scro in the clock neurons abolished Pdf expression and circadian locomotor activity rhythms, and such repressive function requires DNA-binding homeodomain, but none of the other conserved domains. scro is predominantly expressed in the optic lobe and various clusters of cells in other areas of the central nervous system. A homozygous scro-null mutant generated by CRIPSR is lethal during embryonic and early larval development, suggesting that scro plays a vital role during early development.

Two-factor specification of apoptosis: TGF-ß signaling acts cooperatively with ecdysone signaling to induce cell- and stage-specific apoptosis of larval neurons during metamorphosis in Drosophila melanogaster.

Developmentally regulated programmed cell death (PCD) is one of the key cellular events for precise controlling of neuronal population during postembryonic development of the central nervous system. Previously we have shown that a group of corazonin-producing peptidergic neurons (vCrz) undergo apoptosis in response to ecdysone signaling via ecdysone receptor (EcR)-B isoforms and Ultraspiracle during early phase of metamorphosis. Further utilizing genetic, transgenic, and mosaic analyses, we have found that TGF-ß signaling mediated by a glia-produced ligand, Myoglianin, type-I receptor Baboon (particularly Babo-A isoform) and dSmad2, is also required autonomously for PCD of the vCrz neurons. Our studies show that TGF-ß signaling is not acting epistatically to EcR or vice versa. We also show that ectopic expression of a constitutively active phosphomimetic form of dSmad2 (dSmad2PM) is capable of inducing premature death of vCrz neurons in larva but not other larval neurons. Intriguingly, the dSmad2PM-mediated killing is completely suppressed by coexpression of a dominant-negative form of EcR (EcRDN), suggesting that EcR function is required for the proapoptotic dSmad2PM function. Based on these data, we suggest that TGF-ß and ecdysone signaling pathways act cooperatively to induce vCrz neuronal PCD. We propose that this type of two-factor authentication is a key developmental strategy to ensure the timely PCD of specific larval neurons during metamorphosis.

Ultraspiracle-independent anti-apoptotic function of ecdysone receptors is required for the survival of larval peptidergic neurons via suppression of grim expression in Drosophila melanogaster.

In Drosophila melanogaster a significant number of heterogenous larval neurons in the central nervous system undergo metamorphosis-associated programmed cell death, termed metamorphoptosis. Interestingly distinct groups of doomed larval neurons are eliminated at different metamorphic phases. Although ecdysone hormonal signaling via nuclear ecdysone receptors (EcRs) is known to orchestrate the neuronal metamorphoptosis, little is known about how this signaling controls such diverse neuronal responses. Crustacean cardioactive peptide (CCAP)-producing neurons in the ventral nerve cord are developmentally programmed to die shortly after adult emergence. In this study, we show that disruption of endogenous EcR function by ectopic expression of dominant negative forms of EcRs (EcRDN) causes premature death of larval CCAP neurons in a caspase-dependent manner. This event is rescued by co-expression of individual EcR isoforms. Furthermore, larval CCAP neurons are largely normal in ecr mutants lacking either EcR-A or EcR-B isoforms, suggesting that EcR isoforms redundantly function to protect larval CCAP neurons. Of surprise, a role of Ultraspiracle (Usp), a canonical partner of EcR, is dispensable in the protection of CCAP neurons, whereas both EcR and Usp are required for inducing metamorphoptosis of vCrz neurons shortly after prepupal formation. As a downstream, grim is an essential cell death gene for the EcRDN-mediated CCAP neuronal death, while either hid or rpr function is dispensable. Together, our results suggest that Usp-independent EcR actions protect CCAP neurons from their premature death by repressing grim expression until their normally scheduled apoptosis at post-emergence. Our studies highlight two opposite roles played by EcR function for metamorphoptosis of two different peptidergic neuronal groups, proapoptotic (vCrz) versus antiapoptotic (CCAP), and propose that distinct death timings of doomed larval neurons are determined by differential signaling mechanisms involving EcR.

Identifying and monitoring neurons that undergo metamorphosis-regulated cell death (metamorphoptosis) by a neuron-specific caspase sensor (Casor) in Drosophila melanogaster.

Activation of caspases is an essential step toward initiating apoptotic cell death. During metamorphosis of Drosophila melanogaster, many larval neurons are programmed for elimination to establish an adult central nervous system (CNS) as well as peripheral nervous system (PNS). However, their neuronal functions have remained mostly unknown due to the lack of proper tools to identify them. To obtain detailed information about the neurochemical phenotypes of the doomed larval neurons and their timing of death, we generated a new GFP-based caspase sensor (Casor) that is designed to change its subcellular position from the cell membrane to the nucleus following proteolytic cleavage by active caspases. Ectopic expression of Casor in vCrz and bursicon, two different peptidergic neuronal groups that had been well-characterized for their metamorphic programmed cell death, showed clear nuclear translocation of Casor in a caspase-dependent manner before their death. We found similar events in some cholinergic neurons from both CNS and PNS. Moreover, Casor also reported significant caspase activities in the ventral and dorsal common excitatory larval motoneurons shortly after puparium formation. These motoneurons were previously unknown for their apoptotic fate. Unlike the events seen in the neurons, expression of Casor in non-neuronal cell types, such as glial cells and S2 cells, resulted in the formation of cytoplasmic aggregates, preventing its use as a caspase sensor in these cell types. Nonetheless, our results support Casor as a valuable molecular tool not only for identifying novel groups of neurons that become caspase-active during metamorphosis but also for monitoring developmental timing and cytological changes within the dying neurons.

Cloning and functional characterizations of an apoptogenic Hid gene in the Scuttle Fly, Megaselia scalaris (Diptera; Phoridae).

Although the mechanisms of apoptotic cell death have been well studied in the fruit fly, Drosophila melanogaster, it is unclear whether such mechanisms are conserved in other distantly related species. Using degenerate primers and PCR, we cloned a proapoptotic gene homologous to Head involution defective (Hid) from the Scuttle fly, Megaselia scalaris (MsHid). MsHid cDNA encodes a 197-amino acid-long polypeptide, which so far is the smallest HID protein. PCR analyses revealed that the MsHid gene consists of four exons and three introns. Ectopic expression of MsHid in various peptidergic neurons and non-neuronal tissues in Drosophila effectively induced apoptosis of these cells. However, deletion of either conserved domain, N-terminal IBM or C-terminal MTS, abolished the apoptogenic activity of MsHID, indicating that these two domains are indispensable. Expression of MsHid was found in all life stages, but more prominently in embryos and pupae. MsHid is actively expressed in the central nervous system (CNS), indicating its important role in CNS development. Together MsHID is likely to be an important cell death inducer during embryonic and post-embryonic development in this species. In addition, we found 2-fold induction of MsHid expression in UV-irradiated embryos, indicating a possible role for MsHid in UV-induced apoptosis.

Rescheduling Behavioral Subunits of a Fixed Action Pattern by Genetic Manipulation of Peptidergic Signaling.

The ecdysis behavioral sequence in insects is a classic fixed action pattern (FAP) initiated by hormonal signaling. Ecdysis triggering hormones (ETHs) release the FAP through direct actions on the CNS. Here we present evidence implicating two groups of central ETH receptor (ETHR) neurons in scheduling the first two steps of the FAP: kinin (aka drosokinin, leucokinin) neurons regulate pre-ecdysis behavior and CAMB neurons (CCAP, AstCC, MIP, and Bursicon) initiate the switch to ecdysis behavior. Ablation of kinin neurons or altering levels of ETH receptor (ETHR) expression in these neurons modifies timing and intensity of pre-ecdysis behavior. Cell ablation or ETHR knockdown in CAMB neurons delays the switch to ecdysis, whereas overexpression of ETHR or expression of pertussis toxin in these neurons accelerates timing of the switch. Calcium dynamics in kinin neurons are temporally aligned with pre-ecdysis behavior, whereas activity of CAMB neurons coincides with the switch from pre-ecdysis to ecdysis behavior. Activation of CCAP or CAMB neurons through temperature-sensitive TRPM8 gating is sufficient to trigger ecdysis behavior. Our findings demonstrate that kinin and CAMB neurons are direct targets of ETH and play critical roles in scheduling successive behavioral steps in the ecdysis FAP. Moreover, temporal organization of the FAP is likely a function of ETH receptor density in target neurons.

Regulation of ethanol-related behavior and ethanol metabolism by the Corazonin neurons and Corazonin receptor in Drosophila melanogaster.

Impaired ethanol metabolism can lead to various alcohol-related health problems. Key enzymes in ethanol metabolism are alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH); however, neuroendocrine pathways that regulate the activities of these enzymes are largely unexplored. Here we identified a neuroendocrine system involving Corazonin (Crz) neuropeptide and its receptor (CrzR) as important physiological regulators of ethanol metabolism in Drosophila. Crz-cell deficient (Crz-CD) flies displayed significantly delayed recovery from ethanol-induced sedation that we refer to as hangover-like phenotype. Newly generated mutant lacking Crz Receptor (CrzR(01) ) and CrzR-knockdown flies showed even more severe hangover-like phenotype, which is causally associated with fast accumulation of acetaldehyde in the CrzR(01) mutant following ethanol exposure. Higher levels of acetaldehyde are likely due to 30% reduced ALDH activity in the mutants. Moreover, increased ADH activity was found in the CrzR(01) mutant, but not in the Crz-CD flies. Quantitative RT-PCR revealed transcriptional upregulation of Adh gene in the CrzR(01) . Transgenic inhibition of cyclic AMP-dependent protein kinase (PKA) also results in significantly increased ADH activity and Adh mRNA levels, indicating PKA-dependent transcriptional regulation of Adh by CrzR. Furthermore, inhibition of PKA or cAMP response element binding protein (CREB) in CrzR cells leads to comparable hangover-like phenotype to the CrzR(01) mutant. These findings suggest that CrzR-associated signaling pathway is critical for ethanol detoxification via Crz-dependent regulation of ALDH activity and Crz-independent transcriptional regulation of ADH. Our study provides new insights into the neuroendocrine-associated ethanol-related behavior and metabolism.

Mechanisms of postecdysis-associated programmed cell death of peptidergic neurons in Drosophila melanogaster.

Crustacean cardioactive peptide (CCAP)-expressing neurons undergo programmed cell death (PCD) within 24 hours after adult eclosion. A subset of the doomed CCAP neurons in the ventral nerve cord also expressed the neuropeptide bursicon and thus are referred to as bursCCAP neurons. In this study, we undertook comprehensive genetic and transgenic analyses to dissect the PCD mechanisms of bursCCAP neurons. Expression of a versatile caspase inhibitor, p35, blocked PCD of bursCCAP neurons, suggesting caspase-dependent apoptosis. Further genetic analyses showed that Dronc/Dark and Drice are key caspases, but they are not sufficient to carry out the PCD fully. We did not find a role for other known caspases, Strica, Dredd, Damm, or Decay. Of interest, Dcp-1 is required not for the death of bursCCAP neurons per se but for the removal of neural projections. DIAP1 is an important survival factor that inhibits premature death of bursCCAP neurons. We found that grim functions as a principal death inducer, whereas other death genes, hid, reaper, and sickle, show no endogenous function. Taken together with other studies, our work supports the role of grim as a major death inducer particularly for the removal of obsolete larval neurons during CNS metamorphosis. Results from the ectopic expression of the mutant grim lacking either N-terminal IBM or internal GH3 domain indicated that both domains are necessary to induce CCAP cell death.

Essential role of grim-led programmed cell death for the establishment of corazonin-producing peptidergic nervous system during embryogenesis and metamorphosis in Drosophila melanogaster.

In Drosophila melanogaster, combinatorial activities of four death genes, head involution defective (hid), reaper (rpr), grim, and sickle (skl), have been known to play crucial roles in the developmentally regulated programmed cell death (PCD) of various tissues. However, different expression patterns of the death genes also suggest distinct functions played by each. During early metamorphosis, a great number of larval neurons unfit for adult life style are removed by PCD. Among them are eight pairs of corazonin-expressing larval peptidergic neurons in the ventral nerve cord (vCrz). To reveal death genes responsible for the PCD of vCrz neurons, we examined extant and recently available mutations as well as RNA interference that disrupt functions of single or multiple death genes. We found grim as a chief proapoptotic gene and skl and rpr as minor ones. The function of grim is also required for PCD of the mitotic sibling cells of the vCrz neuronal precursors (EW3-sib) during embryonic neurogenesis. An intergenic region between grim and rpr, which, it has been suggested, may enhance expression of three death genes in embryonic neuroblasts, appears to play a role for the vCrz PCD, but not for the EW3-sib cell death. The death of vCrz neurons and EW3-sib is triggered by ecdysone and the Notch signaling pathway, respectively, suggesting distinct regulatory mechanisms of grim expression in a cell- and developmental stage-specific manner.

Dopamine D2 receptor as a cellular component controlling nocturnal hyperactivities in Drosophila melanogaster.

Dysfunctional regulation of brain dopamine (DA) functions has been found in patients with drug addiction and various neurological disorders that frequently accompany disturbance in sleep behavior. In this study, the roles of the dopaminergic nervous system on the regulation of daily locomotor activity rhythm were investigated in Drosophila melanogaster. Reduced synaptic DA release by expressing tetanus toxin gradually attenuated peak activity levels by altering activity patterns, particularly under constant darkness. Besides, flies with a mutant dopamine transporter fumin (fmn), in which the synaptic DA levels were elevated, displayed increased activities in both daytime and nighttime, but did more so at nighttime, suggesting that DA function is involved in regulation of fruit fly's nocturnal locomotor activities. Furthermore, flies treated with bromocriptine, an agonist of Drosophila dopamine D2 receptor (dD2R), exhibited nocturnal locomotor hyperactivity in a dose-dependent manner and this effect was inhibited in dD2R knockdown flies. When mutant flies null for period (per), timeless (tim), dClock (dClk), or cycle (cyc) were treated with bromocriptine, only cycle-null flies (cyc(01)) did not show induced nocturnal hyperactivities, suggesting that cyc might play a role in bromocriptine-induced nocturnal hyperactivities. Elevation of experimental temperature also increased nocturnal activities at the expense of daytime activities. The heat-induced increase in nocturnal activities gradually returned to basal levels at continuously elevated temperature. Inhibition of DA synthesis did not suppress heat-induced early development of nocturnal hyperactivity but prevented gradual decrement of initially elevated nocturnal activities, suggesting that DA impinges on certain adaptive roles in response to changes in environmental temperature. These results overall suggest that controlling dopaminergic transmission is important for daily locomotor behavior and bromocriptine-induced nocturnal hyperactivity which is mediated through dD2R receptor and CYC functions. In parallel to these results, excessive activation of dopaminergic neurotransmission, the primary cause of schizophrenia, is associated with abnormally elevated nocturnal locomotor activities through D2-type receptor in Drosophila. The results suggest that fruit flies are an excellent model system to provide some answers to previously unexplainable observations regarding the compromised dopaminergic nervous system and the related therapeutic agents.

Drosophila caspases involved in developmentally regulated programmed cell death of peptidergic neurons during early metamorphosis.

A great number of obsolete larval neurons in the Drosophila central nervous system are eliminated by developmentally programmed cell death (PCD) during early metamorphosis. To elucidate the mechanisms of neuronal PCD occurring during this period, we undertook genetic dissection of seven currently known Drosophila caspases in the PCD of a group of interneurons (vCrz) that produce corazonin (Crz) neuropeptide in the ventral nerve cord. The molecular death program in the vCrz neurons initiates within 1 hour after pupariation, as demonstrated by the cytological signs of cell death and caspase activation. PCD was significantly suppressed in dronc-null mutants, but not in null mutants of either dredd or strica. A double mutation lacking both dronc and strica impaired PCD phenotype more severely than did a dronc mutation alone, but comparably to a triple dredd/strica/dronc mutation, indicating that dronc is a main initiator caspase, while strica plays a minor role that overlaps with dronc's. As for effector caspases, vCrz PCD requires both ice and dcp-1 functions, as they work cooperatively for a timely removal of the vCrz neurons. Interestingly, the activation of the Ice and Dcp-1 is not solely dependent on Dronc and Strica, implying an alternative pathway to activate the effectors. Two remaining effector caspase genes, decay and damm, found no apparent functions in the neuronal PCD, at least during early metamorphosis. Overall, our work revealed that vCrz PCD utilizes dronc, strica, dcp-1, and ice wherein the activation of Ice and Dcp-1 requires a novel pathway in addition to the initiator caspases.

Comparative analysis of Pdf-mediated circadian behaviors between Drosophila melanogaster and D. virilis.

A group of small ventrolateral neurons (s-LN(v)'s) are the principal pacemaker for circadian locomotor rhythmicity of Drosophila melanogaster, and the pigment-dispersing factor (Pdf) neuropeptide plays an essential role as a clock messenger within these neurons. In our comparative studies on Pdf-associated circadian rhythms, we found that daily locomotor activity patterns of D. virilis were significantly different from those of D. melanogaster. Activities of D. virilis adults were mainly restricted to the photophase under light:dark cycles and subsequently became arrhythmic or weakly rhythmic in constant conditions. Such activity patterns resemble those of Pdf(01) mutant of D. melanogaster. Intriguingly, endogenous D. virilis Pdf (DvPdf) expression was not detected in the s-LN(v)-like neurons in the adult brains, implying that the Pdf(01)-like behavioral phenotypes of D. virilis are attributed in part to the lack of DvPdf in the s-LN(v)-like neurons. Heterologous transgenic analysis showed that cis-regulatory elements of the DvPdf transgene are capable of directing their expression in all endogenous Pdf neurons including s-LN(v)'s, as well as in non-Pdf clock neurons (LN(d)'s and fifth s-LN(v)) in a D. melanogaster host. Together these findings suggest a significant difference in the regulatory mechanisms of Pdf transcription between the two species and such a difference is causally associated with species-specific establishment of daily locomotor activity patterns.