Duchenne and Becker muscular dystrophies are caused by defects of dystrophin, which forms a part of the membrane cytoskeleton of sp d cells such as muscle. It has been previously shown that the dystrophin-asocited protein Al (59-kDa DAP) is actually a heterogeneous group of phosphorylated proteins consisting of an acidic (a-Al) and a distinct basic ((-Al) component. Partial peptide sequence of the Al complex purified from rabbit muscle permitted the design of oligonucleotide probes that were used to isolate a cDNA for one human isoform ofAl. This cDNA encodes a basic Al isoform that is distinct from the recently described syntrophins in Torpedo and mouse and is expressed in many tissues with at least five distinctmRNA speciesof5.9, 4.8, 4.3, 3.1, and 1.5 kb. A comparison of our human cDNA sequence with the GenBank expressed sequence tag (EST) data base has identified a relative from human skeletal muscle, EST25263, which is probably a human homologue of the published mouse syntrophin 2. We have mapped the human basic component of Al and EST25263 genes to chromosomes 8q23-24 and 16, respectively.Dystrophin is the protein product of a large X chromosomeencoded gene that, when defective, can lead to Duchenne and Becker muscular dystrophies (1). When dystrophin is purified from skeletal muscle membranes by absorption onto wheat germ agglutinin-Sepharose, it is found in association with a large oligomeric complex of membrane glycoproteins, the dystrophin-associated glycoprotein (DAG) complex (DAGC) (2). The dystrophin-associated proteins (DAPs) named Al (62 kDa), A2 (52 kDa), A3 (43 kDa), A4 (36 kDa), and A5 (24 kDa), respectively, correspond to the 59-kDa DAP (59-DAP), 50-kDa DAG, 43-kDa DAG, 35-kDa DAG, and 25-kDa DAP reported elsewhere (3, 4). In addition, AO (94 kDa) is distinct from the 156-kDa DAG; the latter stains weakly with Coomp-;sie brilliant blue *1F These proteins, together with dystrcy'in, a-* thought tv participate in the actin-based membrane cytoskeleton of the muscle cell to maintain its stability. The 156-kDa DAG, dystroglycan, biochemically interacts with the extracellular component laminin, functionally implicating dystrophin and the DAGC as a link between the extracellular matrix and the membrane cytoskeleton (5).The site of interaction between dystrophin and the DAGC has been mapped to within the cysteine-rich domain and the first half of the C-terminal domain of dystrophin (6, 7), suggesting that the DAGC may also interact with the C-terminal dystrophin protein of 71 kDa (Dp7l) (8) and the autosomal near-relative of dystrophin, dystrophin-related protein (DRP or utrophin) (9). Al/59-DAP and its Torpedo homologue, 58K (10), have recently been shown by two separate groups to coimmunoprecipitate with dystrophin (11,12). The Torpedo 58K and two homologues in mouse have recently been cloned and named syntrophins (13).A separate study has shown that purified Al/59-DAP consists ofan acidic (a-Al) and a basic ((3-Al) Al population, which can be discriminated by a monoclonal antibody (14 cDNA C...

The cellular localization of the peptide neurotransmitter proctolin was determined for larvae of the fruitfly Drosophila melanogaster. Proctolin was recovered from the CNS, hindgut, and segmental bodywall using reverse-phase HPLC, and characterized by bioassay, immunoassay, and enzymatic analysis. A small, stereotyped population of proctolin-immunoreactive neurons was found in the larval CNS. Several of the identified neurons may be efferents. In the periphery, proctolin-immunoreactive neuromuscular endings were identified on both visceral and skeletal muscle fibers. On the hindgut, the neuropeptide is associated with endings on intrinsic circular muscle fibers. We propose that the hindgut muscle fibers are innervated by central neurons homologous to previously described proctolinergic efferents of grasshoppers. The segmental bodywall innervation consists of a pattern of segment-specific junctions on several singly identifiable muscle fibers. While it is generally accepted that Drosophila muscle fibers are innervated by glutamatergic motoneurons, our data indicate that a specialized subset of muscle fibers are also innervated by peptidergic efferents.

No abstract

No abstract

The neuromuscular connections of Drosophila are ideally suited for studying synaptic function and development. Hypotheses about cell recognition can be tested in a simple array of pre- and postsynaptic elements. Drosophila muscle fibers are multiply innervated by individually identifiable motoneurons. The neurons express several synaptic cotransmitters, including glutamate, proctolin, and octopamine, and are specialized by their synaptic morphology, neurotransmitters, and connectivity. During larval development the initial motoneuron endings grow extensively over the surface of the muscle fibers, and differentiate synaptic boutons of characteristic morphology. While considerable growth occurs postembryonically, the initial wiring of motoneurons to muscle fibers is accomplished during mid-to-late embryogenesis (stages 15-17). Efferent growth cones sample multiple muscle fibers with rapidly moving filopodia. Upon reaching their target muscle fibers, the growth cones rapidly differentiate into synaptic contacts whose morphology prefigures that of the larval junction. Mismatch experiments show that growth cones recognize specific muscle fibers, and can do so when the surrounding musculature is radically altered. However, when denied their normal targets, motoneurons can establish functional synapses on alternate muscle fibers. Blocking synaptic activity with either injected toxins or ion channel mutants does not derange synaptogenesis, but may influence the number of motor ending processes. The molecular mechanisms governing cellular recognition during synaptogenesis remain to be identified. However, several cell surface glycoproteins known to mediate cellular adhesion events in vitro are expressed by the developing synapses. Furthermore, enhancer detector lines have identified genes with expression restricted to small subsets of muscle fibers and/or motoneurons during the period of synaptogenesis. These observations suggest that in Drosophila a mechanism of target chemoaffinity may be involved in the genesis of stereotypic synaptic wiring.

The tripeptide, L-prolyl-L-leucylglycinamide (PLG) reverses the sedative effects of deserpidine in mice and monkeys treated with pargyline and DOPA. It is effective both orally and when injected intraperitoneally, some of its action possibly being exerted upon the catecholamine system.

Abnormalities of dystrophin, a cytoskeletal protein of muscle and nerve, are generally considered specific for Duchenne and Becker muscular dystrophy. However, several patients have recently been identified with dystrophin deficiency who, before dystrophin testing, were considered to have Fukuyama congenital muscular dystrophy (FCMD) on the basis of clinical findings. Epidemiologic data suggest that only 1/3500 males with autosomal recessive FCMD should have abnormal dystrophin. To explain the observation of 3/23 FCMD males with abnormal dystrophin, we propose that dystrophin and the FCMD gene product interact and that the earlier onset and greater severity of these patients' phenotype (relative to Duchenne muscular dystrophy) are due to their being heterozygous for the FCMD mutation in addition to being henizygous for Duchenne muscular dystrophy, a genotype that is predicted to occur in 1/175,000 Japanese males. This model may help explain the genetic basis for some of the clinical and pathological variability seen among patients with FCMD, and it has potential implications for understanding the inheritance of other autosomal recessive disorders in general. For example, sex ratios for rare autosomal recessive disorders caused by mutations in proteins that interact with X chromosome-linked gene products may display predictable deviation from 1:1.

Central dopaminergic (DA) function in children and adults was assessed by monitoring plasma-free levels of the dopamine metabolite homovanillic acid (pHVA) before and after a single oral dose and chronic oral administration of debrisoquin. Debrisoquin inhibits peripheral metabolism of dopamine to HVA and does not cross the blood-brain barrier. By reducing peripheral formation of HVA through the use of debrisoquin, the remaining HVA in plasma more accurately reflects central DA activity. Debrisoquin administration resulted in marked reductions of pHVA in each of 12 patients studied. Eleven of the 12 subjects tolerated debrisoquin without physical or behavioral side effects. The debrisoquin administration method appears to be a safe and potentially valid technique for evaluating aspects of central dopaminergic function in children and adults.