ABSTRACT
Monoclonal antibody 6F8 was used to characterize and clone fasciclin IV, a new axonal glycoprotein in the grasshopper, and to study its function during growth cone guidance. Fasciclin IV is dynamically expressed on a subset of axon pathways in the developing CNS and on circumferential bands of epithelial cells in developing limb buds. One of these bands corresponds to the location where the growth cones of the Ti1 pioneer neurons make a characteristic turn while extending toward the CNS. Embryos cultured in the 6F8 antibody or Fab exhibit aberrant formation of this axon pathway. cDNA sequence analysis suggests that fasciclin IV has a signal sequence; long extracellular, transmembrane, and short cytoplasmic domains; and shows no homology with any protein in the available data bases. Thus, fasciclin IV appears to be a novel integral membrane protein that functions in growth cone guidance.
Subject(s)
Axons/physiology , Cell Adhesion Molecules, Neuronal/genetics , Cell Adhesion Molecules, Neuronal/physiology , Gene Expression , Grasshoppers/embryology , Semaphorins , Amino Acid Sequence , Animals , Antibodies, Monoclonal , Cell Adhesion Molecules, Neuronal/chemistry , DNA/chemistry , DNA/genetics , Epithelium/metabolism , Extremities/embryology , Grasshoppers/genetics , Membrane Proteins/chemistry , Membrane Proteins/genetics , Membrane Proteins/physiology , Molecular Sequence Data , Nervous System/embryology , Nervous System/metabolism , Open Reading FramesABSTRACT
In addition to its expression on subsets of axons, grasshopper Semaphorin I (Sema I, previously called Fasciclin [Fas] IV) is expressed on an epithelial stripe in the limb bud, where it functions in the guidance of two sensory growth cones as they abruptly turn upon encountering this sema I boundary. We report here on the cloning and characterization of two sema genes in Drosophila, one in human, and the identification of two related viral sequences, all of which encode proteins with conserved Semaphorin domains. Drosophila sema (D-Sema) I is a transmembrane protein, while D-Sema II and human Sema III are putative secreted proteins that are similar to the recently reported chick collapsin. D-Sema I and D-Sema II are expressed by subsets of neurons and muscles. Genetic analysis in Drosophila reveals that semall is an essential gene that is required for both proper adult behavior and survival.
Subject(s)
Cell Adhesion Molecules, Neuronal/genetics , Drosophila melanogaster/genetics , Genes, Insect , Nervous System/embryology , Semaphorins , Amino Acid Sequence , Animals , Cloning, Molecular , Drosophila melanogaster/embryology , Gene Expression , Genes , Humans , Molecular Sequence Data , Nervous System/growth & development , Oligodeoxyribonucleotides/chemistry , RNA, Messenger/geneticsABSTRACT
Previous studies showed that grasshopper semaphorin I, a transmembrane semaphorin, functions in vivo to steer a pair of growth cones, prevent defasciculation, and inhibit branching; and that chick collapsin, a secreted semaphorin, can function in vitro to cause growth cone collapse. Semaphorin II, a secreted semaphorin in Drosophila, is transiently expressed by a single large muscle during motoneuron outgrowth and synapse formation. To test the in vivo function of semaphorin II, we created transgenic Drosophila that generate ectopic semaphorin II expression by muscles that normally do not express it. The results show that semaphorin II can function in vivo as a selective target-derived signal that inhibits the formation of specific synaptic terminal arbors.