The IgLON protein Lachesin is required for the blood-brain barrier in Drosophila

In the mammalian peripheral nervous system, nerve insulation depends on the integrity of paranodal junctions between axons and their ensheathing glia. Ultrastructurally, these junctions are similar to the septate junctions (SJ) of invertebrates. In Drosophila, SJ are found in epithelia and in the glia that form the blood-brain barrier (BBB). Drosophila NeurexinIV and Gliotactin, two components of SJ, play an important role in nerve ensheathment and insulation. Here, we report that Drosophila Lachesin (Lac), another SJ component, is also required for a functional BBB. In the developing nervous system, Lac is expressed in a dynamic pattern by surface glia and a subset of neurons. Ultrastructural analysis of Lac mutant embryos shows poorly developed SJ in surface glia and epithelia where Lac is expressed. Mutant embryos undergo a phase of hyperactivity, with unpatterned muscle contractions, and subsequently become paralyzed and fail to hatch. We propose that this phenotype reflects a failure in BBB function.

The inhibitorκB-ortholog Cactus is necessary for normal neuromuscular function in Drosophila melanogaster

The Drosophila inhibitor-kappaB ortholog Cactus acts as an inhibitor of the Rel-transcription factors Dorsal and Dif. In blastoderm cells and immune competent cells, Cactus inhibits Dorsal and Dif by preventing their nuclear localization. Cactus, Dorsal and Dif are also expressed in somatic muscles, where Cactus and Dorsal, but not Dif, are enriched at the neuromuscular junction. Mutations in dorsal cause neuromuscular defects and mislocalization of Cactus. Here, we investigated whether mutations in cactus affect the neuromuscular system and subcellular localization of Dorsal and Dif. Using locomotion assays, as well as physiological and immunochemical methods, we found that wild type Cactus is necessary for the normal function of the larval neuromuscular system. The phenotype comprises i) altered bouton numbers and impaired neurotransmitter release in the neuromuscular junctions in the abdominal segments, ii) muscular weakness and iii) poor locomotion performance, probably reflecting a general neuromuscular impairment. Interestingly, in cactus mutants the subcellular localization of Dorsal and Dif in muscle is not affected, whereas cactus protein is not detected in the nucleus. This suggests, together with the similarities between the phenotypes induced by cactus and dorsal mutations, that in larval muscles the function of Cactus might be cooperation to the transcriptional activity of Rel proteins more than their cytoplasmic retention. The similarities with inhibitor-kappaB/nuclear factor kappaB interactions and muscle pathology in mammals point to Drosophila as a suitable experimental system to clarify the complex interactions of these proteins in muscle postembryonic development and activity.

Real-time, in vivo analysis of malaria ookinete locomotion and mosquito midgut invasion

Invasion of the Anopheles mosquito midgut by the Plasmodium ookinete is a critical step in the malaria transmission cycle. We have generated a fluorescent P. berghei transgenic line that expresses GFP in the ookinete and oocyst stages, and used it to perform the first real-time analysis of midgut invasion in the living mosquito as well as in explanted intact midguts whose basolateral plasma membranes were vitally stained. These studies permitted detailed analysis of parasite motile behaviour in the midgut and cell biological analysis of the invasion process. Throughout its journey, the ookinete displays distinct modes of motility: stationary rotation, translocational spiralling and straight-segment motility. Spiralling is based on rotational motility combined with translocation steps and changes in direction, which are achieved by transient attachments of the ookinete's trailing end. As it moves from the apical to the basal side of the midgut epithelium, the ookinete uses a predominant intracellular route and appears to glide on the membrane in foldings of the basolateral domain. However, it traverses serially the cytoplasm of several midgut cells before entering and migrating through the basolateral intercellular space to access the basal lamina. The invaded cells commit apoptosis, and their expulsion from the epithelium invokes wound repair mechanisms including extensive lamellipodia crawling. A 'hood' of lamellipodial origin, provided by the invaded cell, covers the ookinete during its egress from the epithelium. The flexible ookinete undergoes shape changes and temporary constrictions associated with passage through the plasma membranes. Similar observations were made in both A. gambiae and A. stephensi, demonstrating the conservation of P. berghei interactions with these vectors.

The role of reactive oxygen species on Plasmodium melanotic encapsulation in Anopheles gambiae

Malaria transmission depends on the competence of some Anopheles mosquitoes to sustain Plasmodium development (susceptibility). A genetically selected refractory strain of Anopheles gambiae blocks Plasmodium development, melanizing, and encapsulating the parasite in a reaction that begins with tyrosine oxidation, and involves three quantitative trait loci. Morphological and microarray mRNA expression analysis suggest that the refractory and susceptible strains have broad physiological differences, which are related to the production and detoxification of reactive oxygen species. Physiological studies corroborate that the refractory strain is in a chronic state of oxidative stress, which is exacerbated by blood feeding, resulting in increased steady-state levels of reactive oxygen species, which favor melanization of parasites as well as Sephadex beads.

Drosophila tracheal morphogenesis: intricate cellular solutions to basic plumbing problems

The cellular architecture of tubular organs suggests striking similarities in the mechanisms of tubulogenesis between species. The formation of the Drosophila respiratory organ (trachea) highlights the basic principles of branch patterning and tube growth that generate a highly elaborate but stereotyped epithelial tubular network. Oriented cell migration, changes in cell shape, selective growth of the apical cell membrane and intracellular lumen formation are essential events in this process. These morphogenetic processes build four structurally distinct classes of tubes that facilitate optimal airflow and gas exchange with target tissues. The molecular players in these plots include attractant and repellent signals, differentiation factors that cause a high diversity of cell fates within the epithelium, and determinants of tube formation and dimensions.

Synaptic activity modifies the levels of Dorsal and Cactus at the neuromuscular junction of Drosophila

The Drosophila Rel transcription factor Dorsal and its inhibitor Cactus participate in a signal transduction pathway involved in several biologic processes, including embryonic pattern formation, immunity, and muscle development. In contrast with embryonic muscle, where Dorsal is reportedly absent, this protein and Cactus accumulates in the neuromuscular junctions in the muscle of both larvae and adults. The phenotype of homozygous dorsal mutant larvae suggested that Dorsal and Cactus maybe necessary for normal function and maintenance of the neuromuscular system. Here we investigate if these proteins can respond to synaptic activity. Using larval body wall preparations and antibodies specific for Dorsal or Cactus we show that the amount of these proteins at the neuromuscular junction is substantially decreased after electrical stimulation of the nerves or incubation in glutamate, the principal transmitter in this type of synapse. The specificity of the response was tested with a glutamate receptor antagonist (argiotoxin 636). Because the effect can be reproduced using a calcium ionophore (ionomycin treatment) as well as blocked by the inhibition of the muscle ryanodine receptor (tetracaine treatment), the involvement of calcium in this process seems likely. We also observed that the inhibition of the calcium dependent protein phosphatase calcineurin prevents the effect of glutamate on the fluorescence for Dorsal and Cactus, suggesting its participation in a signal transduction cascade that may activate Dorsal in the muscle independently of Toll. Our results are consistent with a novel function of the Rel factor Dorsal in a molecular pathway turned on by neural activity and/or contractile activity.

Grainy head controls apical membrane growth and tube elongation in response to Branchless/FGF signalling

Epithelial organogenesis involves concerted movements and growth of distinct subcellular compartments. We show that apical membrane enlargement is critical for lumenal elongation of the Drosophila airways, and is independently controlled by the transcription factor Grainy head. Apical membrane overgrowth in grainy head mutants generates branches that are too long and tortuous without affecting epithelial integrity, whereas Grainy head overexpression limits lumenal growth. The chemoattractant Branchless/FGF induces tube outgrowth, and we find that it upregulates Grainy head activity post-translationally, thereby controlling apical membrane expansion to attain its key role in branching. We favour a two-step model for FGF in branching: first, induction of cell movement and apical membrane growth, and second, activation of Grainy head to limit lumen elongation, ensuring that branches reach and attain their characteristic lengths.

Mutations in spalt cause a severe but reversible neurodegenerative phenotype in the embryonic central nervous system of Drosophila melanogaster

The gene spalt is expressed in the embryonic central nervous system of Drosophila melanogaster but its function in this tissue is still unknown. To investigate this question, we used a combination of techniques to analyse spalt mutant embryos. Electron microscopy showed that in the absence of spalt, the central nervous system cells are separated by enlarged extracellular spaces populated by membranous material at 60% of embryonic development. Surprisingly, the central nervous system from slightly older embryos (80% of development) exhibited almost wild-type morphology. An extensive survey by laser confocal microscopy revealed that the spalt mutant central nervous system has abnormal levels of particular cell adhesion and cytoskeletal proteins. Time-lapse analysis of neuronal differentiation in vitro, lineage analysis and transplantation experiments confirmed that the mutation causes cytoskeletal and adhesion defects. The data indicate that in the central nervous system, spalt operates within a regulatory pathway which influences the expression of the beta-catenin Armadillo, its ligand N-Cadherin, Notch, and the cell adhesion molecules Neuroglian, Fasciclin 2 and Fasciclin 3. Effects on the expression of these genes are persistent but many morphological aspects of the phenotype are transient, leading to the concept of sequential redundancy for stable organisation of the central nervous system.

The role of TGFβ signaling in the formation of the dorsal nervous system is conserved betweenDrosophilaand chordates

Transforming growth factor β signaling mediated by Decapentaplegic and Screw is known to be involved in defining the border of the ventral neurogenic region in the fruitfly. A second phase of Decapentaplegic signaling occurs in a broad dorsal ectodermal region. Here, we show that the dorsolateral peripheral nervous system forms within the region where this second phase of signaling occurs. Decapentaplegic activity is required for development of many of the dorsal and lateral peripheral nervous system neurons. Double mutant analysis of the Decapentaplegic signaling mediator Schnurri and the inhibitor Brinker indicates that formation of these neurons requires Decapentaplegic signaling, and their absence in the mutant is mediated by a counteracting repression by Brinker. Interestingly, the ventral peripheral neurons that form outside the Decapentaplegic signaling domain depend on Brinker to develop. The role of Decapentaplegic signaling on dorsal and lateral peripheral neurons is strikingly similar to the known role of Transforming growth factor β signaling in specifying dorsal cell fates of the lateral (later dorsal) nervous system in chordates (Halocythia, zebrafish, Xenopus, chicken and mouse). It points to an evolutionarily conserved mechanism specifying dorsal cell fates in the nervous system of both protostomes and deuterostomes.

Spalt modifies EGFR-mediated induction of chordotonal precursors in the embryonic PNS of Drosophila promoting the development of oenocytes

Genes of the spalt family encode nuclear zinc finger proteins. In Drosophila melanogaster, they are necessary for the establishment of head/trunk identity, correct tracheal migration and patterning of the wing imaginal disc. Spalt proteins display a predominant pattern of expression in the nervous system, not only in Drosophila but also in species of fish, mouse, frog and human, suggesting an evolutionarily conserved role for these proteins in nervous system development. Here we show that Spalt works as a cell fate switch between two EGFR-induced cell types, the oenocytes and the precursors of the pentascolopodial organ in the embryonic peripheral nervous system. We show that removal of spalt increases the number of scolopodia, as a result of extra secondary recruitment of precursor cells at the expense of the oenocytes. In addition, the absence of spalt causes defects in the normal migration of the pentascolopodial organ. The dual function of spalt in the development of this organ, recruitment of precursors and migration, is reminiscent of its role in tracheal formation and of the role of a spalt homologue, sem-4, in the Caenorhabditis elegans nervous system.

members only encodes a Drosophila nucleoporin required for Rel protein import and immune response activation

Many developmental and physiological responses rely on the selective translocation of transcriptional regulators in and out of the nucleus through the nuclear pores. Here we describe the Drosophila genemembers only (mbo) encoding a nucleoporin homologous to the mammalian Nup88. The phenotypes of mbo mutants andmbo expression during development are cell specific, indicating that the nuclear import capacity of cells is differentially regulated. Using inducible assays for nucleocytoplasmic trafficking we show that mRNA export and classic NLS-mediated protein import are unaffected inmbo mutants. Instead, mbo is selectively required for the nuclear import of the yeast transcription factor GAL4 in a subset of the larval tissues. We have identified the first endogenous targets of the mbo nuclear import pathway in the Rel proteins Dorsal and Dif. In mbo mutants the upstream signaling events leading to the degradation of the IκB homolog Cactus are functional, but Dorsal and Dif remain cytoplasmic and the larval immune response is not activated in response to infection. Our results demonstrate that distinct nuclear import events require different nucleoporins in vivo and suggest a regulatory role for mbo in signal transduction.

members only encodes a Drosophila nucleoporin required for rel protein import and immune response activation

Many developmental and physiological responses rely on the selective translocation of transcriptional regulators in and out of the nucleus through the nuclear pores. Here we describe the Drosophila gene members only (mbo) encoding a nucleoporin homologous to the mammalian Nup88. The phenotypes of mbo mutants and mbo expression during development are cell specific, indicating that the nuclear import capacity of cells is differentially regulated. Using inducible assays for nucleocytoplasmic trafficking we show that mRNA export and classic NLS-mediated protein import are unaffected in mbo mutants. Instead, mbo is selectively required for the nuclear import of the yeast transcription factor GAL4 in a subset of the larval tissues. We have identified the first endogenous targets of the mbo nuclear import pathway in the Rel proteins Dorsal and Dif. In mbo mutants the upstream signaling events leading to the degradation of the IkappaB homolog Cactus are functional, but Dorsal and Dif remain cytoplasmic and the larval immune response is not activated in response to infection. Our results demonstrate that distinct nuclear import events require different nucleoporins in vivo and suggest a regulatory role for mbo in signal transduction.

adrift, a novel bnl-induced Drosophila gene, required for tracheal pathfinding into the CNS

Neurons and glial cells provide guidance cues for migrating neurons. We show here that migrating epithelial cells also contact specific neurons and glia during their pathfinding, and we describe the first gene required in the process. In wild-type Drosophila embryos, the ganglionic tracheal branch navigates a remarkably complex path along specific neural and glial substrata, switching substrata five times before reaching its ultimate target in the CNS. In adrift mutants, ganglionic branches migrate normally along the intersegmental nerve, but sporadically fail to switch to the segmental nerve and enter the CNS; they wind up meandering along the ventral epidermis instead. adrift encodes a novel nuclear protein with an evolutionarily conserved motif. The gene is required in the trachea and is expressed in the leading cells of migrating ganglionic branches where it is induced by the branchless FGF pathway. We propose that Adrift regulates expression of tracheal genes required for pathfinding on the segmental nerve, and FGF induction of adrift expression in migrating tracheal cells promotes the switch from the intersegmental to the segmental nerve.

Muscle structure and innervation are affected by loss of Dorsal in the fruit fly, Drosophila melanogaster

In Drosophila, the Rel-protein Dorsal and its inhibitor, Cactus, act in signal transduction pathways that control the establishment of dorsoventral polarity during embryogenesis and the immune response during postembryonic life. Here we present data indicating that Dorsal is also involved in the control of development and maintenance of innervation in somatic muscles. Dorsal and Cactus are colocalized in all somatic muscles during postembryonic development. In larvae and adults, these proteins are distributed at low levels in the cytoplasm and nuclei and at much higher levels in the postsynaptic component of glutamatergic neuromuscular junctions. Absence of Dorsal, in homozygous dorsal mutant larvae results in muscle misinsertions, duplications, nuclear hypotrophy, disorganization of actin bundles, and altered subcellular distribution of Cactus. Some muscles show very abnormal neuromuscular junctions, and some motor axon terminals are transformed into growth cone-like structures embedded in synaptotagmin-enriched vesicles. The detailed phenotype suggests a role of Dorsal signalling in the maintenance and plasticity of the NMJ.

Dif and cactus are colocalized in the larval nervous system of Drosophila melanogaster

The Rel protein Dif is a transcription factor suggested to control part of the immune response in the fruit fly Drosophila melanogaster. In uninfected animals, Dif is normally located in the cytoplasm, most likely in a complex with an IkappaB molecule such as Cactus. Upon infection, Dif is enriched in the nucleus of immunoresponsive tissues such as fat body and blood cells. Rel proteins in mammals not only participate in the control of the immune response, but are also thought to play important roles in the function of the nervous system. Here, we demonstrate that both Dif and Cactus are expressed in the central nervous system (CNS) of Drosophila. Interestingly, Dif and Cactus colocalize in their distribution, suggesting a functional link between these proteins in the CNS. In the larval CNS, both Dif and Cactus are expressed at relatively low levels in most cells and at high levels in the mushroom bodies and in small subsets of neurosecretory cells. The cytoplasmic localization of Dif and Cactus in the CNS cells is not affected by bacterial challenge. Instead, we observed changes in nuclear versus cytoplasmic localization of Cactus (but not Dif) along the dark-light cycle, with a strong nuclear localization in perineurial glia toward the end of the dark period. In the CNS of the prepupa, the intensity of the immunostaining for both Dif and Cactus is higher than in the larva. Interestingly, in fat body of uninfected prepupae, the Dif localization was mainly nuclear, suggesting a function for Dif during the process of pupariation.

Genetic control of epithelial tube fusion during Drosophila tracheal development

During development of tubular networks such as the mammalian vascular system, the kidney and the Drosophila tracheal system, epithelial tubes must fuse to each other to form a continuous network. Little is known of the cellular mechanisms or molecular control of epithelial tube fusion. We describe the cellular dynamics of a tracheal fusion event in Drosophila and identify a gene regulatory hierarchy that controls this extraordinary process. A tracheal cell located at the developing fusion point expresses a sequence of specific markers as it grows out and contacts a similar cell from another tube; the two cells adhere and form an intercellular junction, and they become doughnut-shaped cells with the lumen passing through them. The early fusion marker Fusion-1 is identified as the escargot gene. It lies near the top of the regulatory hierarchy, activating the expression of later fusion markers and repressing genes that promote branching. Ectopic expression of escargot activates the fusion process and suppresses branching throughout the tracheal system, leading to ectopic tracheal connections that resemble certain arteriovenous malformations in humans. This establishes a simple genetic system to study fusion of epithelial tubes.

Electron microscopic analysis of Drosophila midline glia during embryogenesis and larval development using beta-galactosidase expression as endogenous cell marker

To thoroughly study developmental problems it is often desirable to identify specific cells at the resolution of the electron microscope (TEM). Specific antibodies, and immunogold and other antibody labelling techniques can be successfully used with the TEM. But for these techniques to be successful there must be substantial adjustments for each antibody and tissue analyzed. To develop a more generally applicable labelling method we took advantage of the enhancer trap technique in Drosophila. Enhancer trap fly strains show cell- and/or tissue-specific beta-galactosidase expression which can be visualized by a simple X-gal staining procedure. To combine the power of the enhancer trap approach with electron microscopy, we have improved the fixation and staining conditions, which allow detection of X-gal crystals (by TEM) and thus provide precise information on ultrastructural morphology. We have tested our technique using the well-known midline glial cells and examined these cells between late embryonic and pupal developmental stages. The four embryonic midline glial cells found in each neuromere reside ventrally and dorsally to the midline of the neuropile and are closely associated with unpaired neurons, major commissures, and other types of glial cells. During larval and pupal life dramatic cell growth and endomitotic nuclear replication occur in midline glial cells. By the end of larval life, the giant midline glial cells fragment to give rise to a variable number of small midline glial cells. Here we show that the combination of transmission electron microscopy with cytochemical detection of beta-galactosidase expression represents a promising and valuable tool for the study of the morphology and development of specific cell types.

Glial cells in insect ganglia

Glial cells associated with elements of central neuropils in several insect species were studied with conventional light and electron microscopical techniques, the Golgi procedure, and a combination of the latter with electron microscopy. Different types of cells located in the layer of cells covering the neuropil were found to send complex arborizations into synaptic neuropils. These arborizations grow in clusters that seem to represent discrete compartments circumscribing groups of synaptic terminals. The thinnest glial processes are found deep in the neuropil and consist of compact membrane leaflets lacking cell organelles and with reduced amounts of cytoplasmic matrix. Some of these glial processes also invest neuropil tracheoles in a manner reminiscent of the association between astrocyte end-feet and blood capillaries in the central nervous system of mammals. Other glial cells reside completely in the neuropil, where they enwrap fiber bundles in a similar manner to oligodendrocytes in the central nervous system of mammals.

Migration of neurons between ganglia in the metamorphosing insect nervous system

Migration of neurons over long distances occurs during the development of the adult central nervous system of the sphinx moth Manduca sexta, and the turnip moth Agrotis segetum. From each of the suboesophageal and three thoracic ganglia, bilaterally-paired clusters of immature neurons and associated glial cells migrate posteriorly along the interganglionic connectives, to enter the next posterior ganglion. The first sign of migration is observed at the onset of metamorphosis, when posterio-lateral cell clusters gradually separate from the cortex of neuronal cell bodies and enter the connectives. Cell clusters migrate posteriorly along the connective to reach the next ganglion over the first three days (approximately 15%) of pupal development. During migration, each cell cluster is completely enveloped by a single giant glial cell spanning the entire length of the connective between two adjacent ganglia. Intracellular cobalt staining reveals that each migrating neuron has an ovoid cell body and an extremely long leading process which extends as far as the next posterior ganglion; this is not a common morphology for migrating neurons that have been described in vertebrates. Once the cells arrive at the anterior cortex of the next ganglion, they rapidly intermingle with the surrounding neurons and so we were unable to determine the fate of the migrating neurons at their final location.

Evidence that locustatachykinin I is involved in release of adipokinetic hormone from locust corpora cardiaca

The glandular cells of the corpus cardiacum of the locust Locusta migratoria, known to synthesize and release adipokinetic hormones (AKH), are contacted by axons immunoreactive to an antiserum raised against the locust neuropeptide locustatachykinin I (LomTK I). Electron-microscopical immunocytochemistry reveals LomTK immunoreactive axon terminals, containing granular vesicles, in close contact with the glandular cells cells. Release of AKH I from isolated corpora cardiaca of the locust has been monitored in an in vitro system where the amount of AKH I released into the incubation saline is determined by reversed phase high performance liquid chromatography with fluorometric detection. We could show that LomTK I induces release of AKH from corpora cardiaca in a dose-dependent manner when tested in a range of 10-200 microM. This is thus the first clear demonstration of a substance inducing release of AKH, correlated with the presence of the substance in fibers innervating the AKH-synthesizing glandular cells, in the insect corpora cardiaca.

Postembryonic development of corazonin-containing neurons and neurosecretory cells in the blowfly, Phormia terraenovae

An antiserum against the cockroach cardioactive peptide corazonin was used to investigate the distribution of immunoreactive neurons and neurosecretory cells in the nervous system of the blowfly, Phormia terraenovae, during postembryonic development. A small number of corazonin-immunoreactive neurons was found at larval, pupal, and adult stages. At all postembryonic stages two cell groups were found in the protocerebrum of the brain: 1) two lateral cell clusters and 2) two median cells. In the larva eight bilateral cell pairs were found in thoracic and abdominal neuromeres of the fused ventral ganglion. The lateral brain neurons are located in the lateral neurosecretory cell group and extend axons with branches in several components of the retrocerebral neuroendocrine complex, in the stomatogastric nervous system of larvae and adults, and additionally in muscles of the alimentary canal in the adult. The most prominent element of these peripheral processes is a large plexus of varicose fibers located in the wall of the aorta, the main site for the release of neurohormones produced in the brain of blowflies. The presence of corazonin-immunoreactive material in the aortic plexus suggests that this peptide functions as a neurohormone. During metamorphosis, the immunoreactive neurons found in the thoracic-abdominal ganglion of the larva disappear, and in the brain new immunoreactive neurons are added to those that persist from larval stages. The bulk of the corazonin-immunoreactive material extracted from adult brains and corpora cardiaca-aorta complexes was found to co-elute with synthetic corazonin in reversed-phase high-performance liquid chromatography as monitored with enzyme-linked immunosorbent assay.

Segmental peptidergic innervation of abdominal targets in larval and adult dipteran insects revealed with an antiserum against leucokinin I

An antiserum against the cockroach neuropeptide leucokinin I (LKI) was used to study peptidergic neurons and their innervation patterns in larvae and adults of three species of higher dipteran insects, the flies Drosophila melanogaster, Calliphora vomitoria, and Phormia terraenovae, as well as larvae of a primitive dipteran insect, the crane fly Phalacrocera replicata. In the larvae of the higher dipteran flies, the antiserum revealed three pairs of cells in the brain, three pairs of ventro-medial cells in the subesophageal ganglion, and seven pairs of ventro-lateral cells in the abdominal ganglia. Each of these 14 abdominal leucokinin-immunoreactive (LKIR) neurons innervates a single muscle of the abdominal body wall (muscle 8), which is known to degenerate shortly after adult emergence. Conventional electron microscopy demonstrates that this muscle is innervated by at least one axon containing clear vesicles and two axons containing dense-cored vesicles. Electron-microscopical immunocytochemistry shows that the LKIR axon is one of these two axons with dense-cored vesicles and that it forms terminals on the sarcolemma of its target muscle. The abdominal LKIR neurons appear to survive metamorphosis. In the adult fly, the efferent abdominal LKIR neurons innervate the spiracles, the heart, and neurohemal regions of the abdominal wall. In the crane fly larva, dorso-medial and ventrolateral LKIR cell bodies are located in both thoracic and abdominal ganglia of the ventral nerve cord. As in the larvae of the other flies, the abdominal ventrolateral LKIR neurons form efferent axons. However, in the crane fly larva there are two pairs of efferent LKIR neurons in each of the abdominal ganglia and their peripheral targets include neurohemal regions of the dorsal transverse nerves. An additional difference is that in the crane fly, a caudal pair of LKIR axons originating from the penultimate pair of dorso-median LKIR cells in the terminal ganglion innervate the hind-gut.