Millington, Grethel et al. (2013) International Worm Meeting "A forward genetic screen identifies modifiers of a voltage- and Ca2+-activated K+ channel in left-right neuronal asymmetry."

Chang, Chieh, Chuang, Chiou-Fen, Millington, Grethel

[International Worm Meeting, 2013]

The developing nervous system generates a large diversity of cell types with distinct patterns of gene expression and functions. One way to establish neuronal diversity is to specify neuronal subtypes across the left-right axis. The C. elegans left and right AWC olfactory neurons communicate to specify asymmetric subtypes, AWCOFF and AWCON. The default AWCOFF is specified by a Ca2+ regulated kinase cascade that is activated by influx of Ca2+ through the voltage-gated Ca2+ channel UNC-2/UNC-36. Intercellular communication between the two AWC neurons and other neurons through the NSY-5/innexin gap junction network antagonizes unc-2/unc-36 Ca2+ signaling in the induced AWCON cell. However, the mechanisms by which nsy-5 inhibits unc-2/unc-36 Ca2+ signaling is largely unknown. A previous study implicated a role of SLO-1 (Ca2+-activated large conductance "BK" K+ channel) in promoting AWCON. However, how slo-1 regulates AWCON choice has not been studied. Activation of vertebrate SLO-1 channels causes transient membrane hyperpolarization, which makes it an important negative feedback system for Ca2+ entry through voltage-activated Ca2+ channels. Consistent with the physiological roles of SLO-1, our data suggest that slo-1 acts downstream of nsy-5 to inhibit unc-2/unc-36 Ca2+ signaling in the specification of AWCON. To identify the genes required for slo-1 function in inhibiting unc-2/unc-36 Ca2+ signaling for promoting AWCON, we performed a non-biased forward genetic screen to isolate mutants that suppress the slo-1(gf) phenotype. vy11 is one of the mutants identified from this screen. The phenotype of vy11 mutants is suppressed by loss-of-function mutations in the Ca2+ channel gene unc-36, suggesting that the vy11 gene acts upstream of the unc-2/unc-36 Ca2+ signaling pathway. Together, our results suggest a model in which nsy-5 inhibits unc-2/unc-36 Ca2+ signaling through slo-1 and the vy11 gene. Our ongoing cloning of the vy11 gene will elucidate the underlying molecular mechanisms of the model.

Alqadah, Amel et al. (2015) International Worm Meeting "SLO K+ channels couple gap junctions to inhibit Ca2+ signaling in olfactory neuron diversification."

Yi-Wen, Hsieh, Grethel, Millington, Jennifer A., Schumacher, Alqadah, Amel, Xiaohong, Wang, Brittany, Bayne, Chiou-Fen, Chuang

[International Worm Meeting, 2015]

The nervous system generates a tremendous diversity of cell types that enable formation of functional neural circuits for information processing and mediating behaviors. Cellular diversity is especially important in the developing sensory system as it allows animals to detect different cues in the environment. However, the molecular mechanisms that generate neuronal diversification are not yet fully revealed. One way to generate cellular diversity in the nervous system is to specify different fates and functions of individual cell types across the left-right axis. Left-right asymmetry in the nervous system is present throughout the animal kingdom. The C. elegans AWC olfactory neuron pair communicates to specify asymmetric subtypes, AWCOFF and AWCON across the left-right axis. The default AWCOFF is specified by a Ca2+-regulated kinase cascade that is activated by influx of Ca2+ through the voltage-gated Ca2+ channel UNC-2/UNC-36. Intercellular communication between AWC and other neurons in a transient NSY-5 gap junction network antagonizes UNC-2/UNC-36 calcium channels in the future AWCON cell, but how calcium signaling is downregulated by NSY-5 is only partly understood.We show that voltage- and calcium-activated SLO BK potassium channels mediate gap junction signaling to inhibit calcium pathways for asymmetric AWC differentiation. Activation of vertebrate SLO-1 channels causes transient membrane hyperpolarization, which makes it an important negative feedback system for calcium entry through voltage-activated calcium channels. Consistent with the physiological roles of SLO-1, our genetic results suggest that slo-1 and slo-2 act redundantly downstream of nsy-5 to inhibit unc-2/unc-36 Ca2+ signaling in the specification of AWCON. nsy-5-dependent asymmetric expression of slo-1/slo-2 in the AWCON neuron is necessary and sufficient for AWC asymmetry. SLO-1/SLO-2 localize close to UNC-2 in AWC, consistent with functional coupling between these channels in AWC asymmetry. Furthermore, slo-1/slo-2 regulate synaptic communication between AWC neurons to control AWC asymmetry. Together, these results provide an unprecedented molecular link between gap junctions and calcium pathways for terminal neuron differentiation.