Growth cone behavior underlying the development of stereotypic synaptic connections in Drosophila embryos

Abstract

Each muscle fiber in the segmented body wall of Drosophila larvae is innervated by anatomically stereotyped neuromuscular junctions. These synapses arise through the selective choices of motoneuronal growth cones at their peripheral targets. Using digital optical microscopy of staged intracellular dye fills, we have singly identified embryonic motoneurons and have examined individual growth cones when they contact and differentiate at the target cells. There is a precise connectivity between motoneuron and muscle fiber, which is the direct consequence of growth cone behavior. We have also found that Drosophila muscle fibers possess molecularly heterogeneous cell surfaces that may be involved in growth cone recognition of appropriate targets. Fasciclin III, a homophilic adhesion molecule, is coexpressed by several of the efferent growth cones and in a site-specific fashion by the target muscle fiber's membrane. The fasciclin III expression is transient, corresponding to the period in embryogenesis when the first neuromuscular contacts are made. Upon encountering the target cell surface, the growth cones can sprout stereotypically arrayed filopodial processes, orient along the anterior-posterior axis, and turn in predictable directions. Subsequently, terminal branches are established in a nonrandom order. These phenomena were found to occur in two motoneurons that innervate adjacent muscle fiber targets, and may be general features of neuromuscular synaptogenesis in Drosophila.

Spatial and Temporal Control of Gene Expression in Drosophila Using the Inducible GeneSwitch GAL4 System. I. Screen for Larval Nervous System Drivers

“…The coverslips were then mounted on a microscope slide and examined under fluorescent epiillumination using a 103 0.45 NA planapochromatic objective. For the secondary F 1 screen, four to six filleted larval body wall preparations (Halpern et al 1991) from each enhancer-trap line retained after the primary screen were examined by whole-field epifluorescence.…”

“…Immunohistohemistry: Filleted larval body wall preparations (Halpern et al 1991) were fixed in 4% paraformaldehye for 1 hr, followed by 4 3 15-min washes in phosphate-buffered saline (0.9% NaCl, 10 mm NaH 2 PO 4 , pH 7.2) containing 0.3% Triton X-100 (TBS), blocked for 1 hr in 1% BSA in TBS, and incubated in primary antibody overnight at 4°. After 4 3 15-min washes in TBS, larvae were incubated in secondary antibody for 4 hr at room temperature, washed 4 3 15 min in TBS, and mounted in antifade (Invitrogen, San Diego).…”

Target recognition at the tips of postsynaptic filopodia: accumulation and function of Capricious

“…5CЈ). By this stage, MN13s (including RP1 and RP4 neurons) had begun to arborize along the proximal edge of M13 (Sink and Whitington, 1991;Halpern et al, 1991). By contrast, the growth cones of MN12s (including RP5) had moved to a more distal region.…”

A neurotransmitter transporter encoded by the Drosophila inebriated gene

“…Several transmitters have been reported at the motor nerve terminal that could be potential substrates for the ine transporter. These transmitters include glutamate itself and octopamine (40,41). Alternatively, the signaling system could result from intercellular communication between an interneuron and its target motor neuron (Fig.…”