The insect homologue of the amyloid precursor protein interacts with the heterotrimeric G protein Go alpha in an identified population of migratory neurons.

The amyloid precursor protein (APP) is the source of Abeta fragments implicated in the formation of senile plaques in Alzheimer's disease (AD). APP-related proteins are also expressed at high levels in the embryonic nervous system and may serve a variety of developmental functions, including the regulation of neuronal migration. To investigate this issue, we have cloned an orthologue of APP (msAPPL) from the moth, Manduca sexta, a preparation that permits in vivo manipulations of an identified set of migratory neurons (EP cells) within the developing enteric nervous system. Previously, we found that EP cell migration is regulated by the heterotrimeric G protein Goalpha: when activated by unknown receptors, Goalpha induces the onset of Ca2+ spiking in these neurons, which in turn down-regulates neuronal motility. We have now shown that msAPPL is first expressed by the EP cells shortly before the onset of migration and that this protein undergoes a sequence of trafficking, processing, and glycosylation events that correspond to discrete phases of neuronal migration and differentiation. We also show that msAPPL interacts with Goalpha in the EP cells, suggesting that msAPPL may serve as a novel G-protein-coupled receptor capable of modulating specific aspects of migration via Goalpha-dependent signal transduction.

Remodeling of motor terminals during metamorphosis of the moth Manduca sexta: expression patterns of two distinct isoforms of Manduca fasciclin II.

During metamorphosis of the moth Manduca sexta, the neuromuscular system of the thoracic legs is reorganized dramatically. Larval leg muscles degenerate at the end of larval life, and new adult leg muscles develop during the ensuing pupal stage. Larval leg motoneurons persist, but undergo substantial remodeling of central and peripheral processes. As part of our on-going investigation of mechanisms underlying the remodeling of motor terminals, we have used antisera generated against Manduca-specific isoforms of the homophilic adhesion molecule fasciclin II (MFas II) to label motor terminals during metamorphosis. Antisera generated against the glycosyl-phosphatidylinositol (GPI) -linked isoform of MFas II (GPI-MFas II) labeled the motor nerves at all stages and seemed to be associated with glial cells ensheathing the peripheral nerves. In addition, the anti-GPI-MFas II antisera labeled regions associated with synaptic boutons at both larval and adult stages. In contrast, antisera generated against a transmembrane isoform of MFas II (TM-MFas II) only labeled specific neuronal processes at discrete intervals during remodeling. Identified leg motoneurons (such as the femoral depressor motoneuron) expressed detectable levels of TM-MFas II in their peripheral processes only during phases of motor-terminal retraction and initial stages of motor-terminal re-growth. Putative modulatory neurons (such as the unpaired median neurons), however, expressed TM-MFas II in their processes during larval stages as well as during remodeling. Use of the isoform-specific anti-MFas II antisera provided a novel method for visualizing remodeling of motor terminals during metamorphosis and helped distinguish different components of the motor nerves and neuromuscular junction.

Sex-specific differentiation of a male-specific abdominal muscle, the Muscle of Lawrence, is abnormal in hydroxyurea-treated and in fruitless male flies.

A prominent sex-specific abdominal muscle in male Drosophila is the Muscle of Lawrence (MOL), which is induced by male-specific innervation. We have examined MOL development in wild-type males, in males fed hydroxyurea to ablate the muscle precursors and in fruitless mutants, in which the MOL muscle develops aberrantly. One striking feature of MOLs in wild-type males was the presence of additional muscle nuclei compared with neighboring muscles or MOL-homologues in females. We tested whether muscle length and the sex-specific expression of a reporter gene depended critically on the number of nuclei present within a MOL fiber. MOL fibers developing from a reduced myoblast pool in hydroxyurea-affected hemisegments were recognizable by their attachment points and still contained more nuclei than did neighboring medial fibers, suggesting that these MOL fibers were able to actively recruit myoblasts nearly as well as wild-type MOLs. However, many of the hydroxyurea-affected MOL fibers were incapable of the normal male-specific expression of a muscle-specific reporter gene. We suggest that early events in MOL development, such as finding the correct muscle attachment points, are relatively insensitive to the number of MOL nuclei compared with later events, such as the sex-specific expression of a reporter gene. In fruitless mutant males, MOL-position fibers are smaller and had substantially fewer nuclei compared to wild-type MOLs. Since the number and distribution of muscle precursors was the same in fruitless mutant and wild-type animals, we propose that one fru+ function is to direct the male-specific recruitment of myoblasts into MOL-myotubes. However, fruitless+ must have more than one role in MOL fiber development, since simple reduction in the number of muscle nuclei, as demonstrated by the hydroxyurea ablations, is insufficient to account for all of the MOL muscle phenotypes in fruitless mutant males.