Multiple doublesex-Related Genes Specify Critical Cell Fates in a C. elegans Male Neural Circuit

Abstract

BackgroundIn most animal species, males and females exhibit differences in behavior and morphology that relate to their respective roles in reproduction. DM (Doublesex/MAB-3) domain transcription factors are phylogenetically conserved regulators of sexual development. They are thought to establish sexual traits by sex-specifically modifying the activity of general developmental programs. However, there are few examples where the details of these interactions are known, particularly in the nervous system.Methodology/Principal FindingsIn this study, we show that two C. elegans DM domain genes, dmd-3 and mab-23, regulate sensory and muscle cell development in a male neural circuit required for mating. Using genetic approaches, we show that in the circuit sensory neurons, dmd-3 and mab-23 establish the correct pattern of dopaminergic (DA) and cholinergic (ACh) fate. We find that the ETS-domain transcription factor gene ast-1, a non-sex-specific, phylogenetically conserved activator of dopamine biosynthesis gene transcription, is broadly expressed in the circuit sensory neuron population. However, dmd-3 and mab-23 repress its activity in most cells, promoting ACh fate instead. A subset of neurons, preferentially exposed to a TGF-beta ligand, escape this repression because signal transduction pathway activity in these cells blocks dmd-3/mab-23 function, allowing DA fate to be established. Through optogenetic and pharmacological approaches, we show that the sensory and muscle cell characteristics controlled by dmd-3 and mab-23 are crucial for circuit function.Conclusions/SignificanceIn the C. elegans male, DM domain genes dmd-3 and mab-23 regulate expression of cell sub-type characteristics that are critical for mating success. In particular, these factors limit the number of DA neurons in the male nervous system by sex-specifically regulating a phylogenetically conserved dopamine biosynthesis gene transcription factor. Homologous interactions between vertebrate counterparts could regulate sex differences in neuron sub-type populations in the brain.

TGF-β signaling in C. elegans

“…To specify ray identities, DBL-1 pathway signaling regulates the expression of two transcription factors. DBL-1 pathway activity establishes dopaminergic fates in the A neurons of rays 5, 7, and 9 by blocking the activity of DMD-3/ DM (Doublesex/MAB-3) domain transcription factor (Siehr et al, 2011). DBL-1 pathway signaling is required for the expression of ceh-13 / labial Hox family transcription factor in the Bγ rectal blast cell lineage and ray complexes 5, 7, and 9, though males lacking ceh-13 still have functional copulatory structures (Stoyanov et al, 2003).…”

The roles of Dmrt (Double sex/Male-abnormal-3 Related Transcription factor) genes in sex determination and differentiation mechanisms: Ubiquity and diversity across the animal kingdom

“…Later studies showed that mab-3, which represses the transcription of genes related to the production of yolk proteins [25], is required for transcription of male-specific genes in sensory neurons of the head and tail [26][27][28] and is necessary for male-specific muscle differentiation [29]. Behavioral assays showed that male mab-3 mutants present deficits in attraction to and interaction with hermaphrodites [27].…”

“…Male mab-23 mutants have morphological abnormalities in their tails, gonads and nervous system, and are unable to sire progeny. In males, mab-23 has been implicated in the patterning of the nervous system [28,29], the development of male-specific muscles [28,29] and the development of ''+'' and ''++'': low and high level of expression respectively; ''-'': no expression detected; NP: not performed.…”

“…the proctodeum [28]. Mab-23 mutants are defective in the stereotyped sequence of copulatory behavior and show impairments in the transfer of sperm during copulation [28,29].…”

“…Mab-23 mutants are defective in the stereotyped sequence of copulatory behavior and show impairments in the transfer of sperm during copulation [28,29]. In hermaphrodites, mab-23 is expressed in both sex-and non-sex-specific tissues; however, hermaphrodite mab-23 mutants do not show any detectable phenotype, suggesting that this gene is unnecessary or functionally redundant in hermaphrodites [29].…”