Two chemoreceptors mediate developmental effects of dauer pheromone in C. elegans

Olfactory plasticity is regulated by pheromonal signaling in Caenorhabditis elegans

Population density-dependent dispersal is a well-characterized strategy of animal behavior in which dispersal rate increases when population density is higher. Caenorhabditis elegans shows positive chemotaxis to a set of odorants, but the chemotaxis switches from attraction to dispersal after prolonged exposure to the odorants. We show here that this plasticity of olfactory behavior is dependent on population density and that this regulation is mediated by pheromonal signaling. We show that a peptide, suppressor of NEP-2 (SNET-1), negatively regulates olfactory plasticity and that its expression is down-regulated by the pheromone. NEP-2, a homolog of the extracellular peptidase neprilysin, antagonizes SNET-1, and this function is essential for olfactory plasticity. These results suggest that population density information is transmitted through the external pheromone and endogenous peptide signaling to modulate chemotactic behavior.

The homeodomain protein hmbx-1 maintains asymmetric gene expression in adult C. elegans olfactory neurons

Differentiated neurons balance the need to maintain a stable identity with their flexible responses to dynamic environmental inputs. Here we characterize these opposing influences on gene expression in Caenorhabditis elegans olfactory neurons. Using transcriptional reporters that are expressed differentially in two olfactory neurons, AWC(ON) and AWC(OFF), we identify mutations that affect the long-term maintenance of appropriate chemoreceptor expression. A newly identified gene from this screen, the conserved transcription factor hmbx-1, stabilizes AWC gene expression in adult animals through dosage-sensitive interactions with its transcriptional targets. The late action of hmbx-1 complements the early role of the transcriptional repressor gene nsy-7: Both repress expression of multiple AWC(OFF) genes in AWC(ON) neurons, but they act at different developmental stages. Environmental signals are superimposed onto this stable cell identity through at least two different transcriptional pathways that regulate individual chemoreceptor genes: a cGMP pathway regulated by sensory activity, and a daf-7 (TGF-beta)/daf-3 (SMAD repressor) pathway regulated by specific components of the density-dependent C. elegans dauer pheromone.

Histone tales: echoes from the past, prospects for the future

Recent studies of the nematode dauer state provide new insights into epigenetic processes that underlie cellular memory.

Recent studies of the nematode dauer state provide new insights into epigenetic processes that underlie cellular memory.

The HMX/NKX homeodomain protein MLS-2 specifies the identity of the AWC sensory neuron type via regulation of the ceh-36 Otx gene in C. elegans

The differentiated features of postmitotic neurons are dictated by the expression of specific transcription factors. The mechanisms by which the precise spatiotemporal expression patterns of these factors are regulated are poorly understood. In C. elegans, the ceh-36 Otx homeobox gene is expressed in the AWC sensory neurons throughout postembryonic development, and regulates terminal differentiation of this neuronal subtype. Here, we show that the HMX/NKX homeodomain protein MLS-2 regulates ceh-36 expression specifically in the AWC neurons. Consequently, the AWC neurons fail to express neuron type-specific characteristics in mls-2 mutants. mls-2 is expressed transiently in postmitotic AWC neurons, and directly initiates ceh-36 expression. CEH-36 subsequently interacts with a distinct site in its cis-regulatory sequences to maintain its own expression, and also directly regulates the expression of AWC-specific terminal differentiation genes. We also show that MLS-2 acts in additional neuron types to regulate their development and differentiation. Our analysis describes a transcription factor cascade that defines the unique postmitotic characteristics of a sensory neuron subtype, and provides insights into the spatiotemporal regulatory mechanisms that generate functional diversity in the sensory nervous system.