At chemical synapses, neurotransmitters are packaged into synaptic vesicles that release their contents in response to depolarization. Despite its central role in synaptic function, regulation of the machinery that loads vesicles with neurotransmitters remains poorly understood. We find that synaptic glutamate signaling in a C. elegans chemosensory circuit is regulated by antagonistic interactions between the canonical vesicular glutamate transporter EAT-4/VGLUT and another vesicular transporter, VST-1. Loss of VST-1 strongly potentiates glutamate release from chemosensory BAG neurons and disrupts chemotaxis behavior. Analysis of the circuitry downstream of BAG neurons shows that excess glutamate release disrupts behavior by inappropriately recruiting RIA interneurons to the BAG-associated chemotaxis circuit. Our data indicate that in vivo the strength of glutamatergic synapses is controlled by regulation of neurotransmitter packaging into synaptic vesicles via functional coupling of VGLUT and VST-1.

Nervous system development is instructed by genetic programs and refined by distinct mechanisms that couple neural activity to gene expression. How these processes are integrated remains poorly understood. Here, we report that the regulated release of insulin-like peptides (ILPs) during development of the Caenorhabditis elegans nervous system accomplishes such an integration. We find that the p38 MAP kinase PMK-3, which is required for the differentiation of chemosensory BAG neurons, limits an ILP signal that represses expression of a BAG neuron fate. ILPs are released from BAGs themselves in an activity-dependent manner during development, indicating that ILPs constitute an autocrine signal that regulates the differentiation of BAG neurons. Expression of a specialized neuronal fate is, therefore, coordinately regulated by a genetic program that sets levels of ILP expression during development, and by neural activity, which regulates ILP release. Autocrine signals of this kind might have general and conserved functions as integrators of deterministic genetic programs with activity-dependent mechanisms during neurodevelopment.

24Nervous system development is instructed both by genetic programs and activity-dependent 25 refinement of gene expression and connectivity. How these mechanisms are integrated remains 26 poorly understood. Here, we report that the regulated release of insulin-like peptides (ILPs) 27 during development of the C. elegans nervous system accomplishes such an integration. We 28 find that the p38 MAP kinase PMK-3, which is required for the differentiation of chemosensory 29 BAG neurons, functions by limiting expression of an autocrine ILP signal that represses a 30 chemosensory-neuron fate. ILPs are released from BAGs in an activity-dependent manner 31 during embryonic development, and regulate neurodifferentiation through a non-canonical 32 insulin receptor signaling pathway. The differentiation of a specialized neuron-type is, therefore, 33 coordinately regulated by a genetic program that controls ILP expression and by neural activity, 34 which regulates ILP release. Autocrine signals of this kind may have general and conserved 35 functions as integrators of deterministic genetic programs with activity-dependent mechanisms 36 during neurodevelopment. 37 38 2017). How these two different mechanisms -one specified and the other activity-dependent -47 are integrated during nervous system development remains poorly understood. 48The C. elegans nervous system displays a wide range of neuronal diversity, and is a 49 powerful model to study neuronal differentiation (White et al. 1986;Hobert et al. 2016). The 50 mostly invariant cell lineage that generates the C. elegans nervous system (Sulston 1977; 51 Sulston 1983) suggests that neuronal differentiation in C. elegans is principally determined by 52 genetic programs intrinsic to the cell-lineage. Indeed, many studies have identified transcription 53 factors that act in specific sub-lineages to promote specific neural fates (Hobert 2016). However, 54there are also important roles for neuronal activity during development of the C. elegans nervous 55 system. For example, there is a striking role for activity of embryonic AWC chemosensory 56 neurons in determining their differentiation into functionally distinct subtypes (Troemel 1999; 57 Sagasti 2001). More recently, it has been found that there is a critical period during which neural 58 activity instructs circuit assembly in the C. elegans motor system (Barbagallo et al. 2017). Post-59 developmentally, neural and sensory activity is required for maintaining the proper morphology 60 of chemosensory neurons (Peckol 1999; Mukhopadhyay et al. 2008), and for expression of 61 chemosensory receptors and neuropeptides that define specific chemosensory neuron fates 62 (Peckol et al. 2001; Gruner et al. 2014; Rojo Romanos et al. 2017). Like the vertebrate nervous 63 system, therefore, development of the C. elegans nervous system requires both lineally 64 programmed gene regulation and neural activity. 65 We have investigated mechanisms required for the development of a pair of C. elegans 66 sensory neurons -the BAGs, which se...

At chemical synapses, neurotransmitters are packaged into synaptic vesicles that release their contents in response to depolarization. Despite its central role in synaptic function, regulation of the machinery that loads vesicles with neurotransmitters remains poorly understood. We find that synaptic glutamate signaling in a C. elegans chemosensory circuit is regulated by antagonistic interactions between the canonical vesicular glutamate transporter EAT-4/VGLUT and another vesicular transporter, VST-1. Loss of VST-1 strongly potentiates glutamate release from chemosensory BAG neurons and disrupts chemotaxis behavior. Analysis of the circuitry downstream of BAG neurons shows that excess glutamate release disrupts behavior by inappropriately recruiting RIA interneurons to the BAG-associated chemotaxis circuit. Our data indicate that in vivo the strength of glutamatergic synapses is controlled by regulation of neurotransmitter packaging into synaptic vesicles via functional coupling of VGLUT and VST-1.