A chromosome walk linking the gatA and alcC genes of Aspergillus nidulans

The amdA gene of Aspergillus nidulans has been mapped to linkage group VII, between the gatA and alcC genes (Jones and Sealy- Lewis 1990 Curr. Genet. 17:81-85). As clones of both of the genes flanking amdA were available, they were used as starting points for chromosome walking towards amdA. The relative orientation of these genes on linkage group VII was not known at the time. Therefore, both walks extended in both directions until overlapping clones from the different walks were detected. The total distance covered by all walks is approximately 240 kb

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

In 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.In 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.In 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

A Cholinergic-Regulated Circuit Coordinates the Maintenance and Bi-Stable States of a Sensory-Motor Behavior during Caenorhabditis elegans Male Copulation

Penetration of a male copulatory organ into a suitable mate is a conserved and necessary behavioral step for most terrestrial matings; however, the detailed molecular and cellular mechanisms for this distinct social interaction have not been elucidated in any animal. During mating, the Caenorhabditis elegans male cloaca is maintained over the hermaphrodite's vulva as he attempts to insert his copulatory spicules. Rhythmic spicule thrusts cease when insertion is sensed. Circuit components consisting of sensory/motor neurons and sex muscles for these steps have been previously identified, but it was unclear how their outputs are integrated to generate a coordinated behavior pattern. Here, we show that cholinergic signaling between the cloacal sensory/motor neurons and the posterior sex muscles sustains genital contact between the sexes. Simultaneously, via gap junctions, signaling from these muscles is transmitted to the spicule muscles, thus coupling repeated spicule thrusts with vulval contact. To transit from rhythmic to sustained muscle contraction during penetration, the SPC sensory-motor neurons integrate the signal of spicule's position in the vulva with inputs from the hook and cloacal sensilla. The UNC-103 K+ channel maintains a high excitability threshold in the circuit, so that sustained spicule muscle contraction is not stimulated by fewer inputs. We demonstrate that coordination of sensory inputs and motor outputs used to initiate, maintain, self-monitor, and complete an innate behavior is accomplished via the coupling of a few circuit components

Regulation of sex-specific differentiation and mating behavior in C. elegans by a new member of the DM domain transcription factor family

Mutations in Caenorhabditis elegans gene mab-23 cause abnormal male tail morphology and abolish male fecundity but have no obvious effect in the hermaphrodite. Here we show that mab-23 encodes a DM (Doublesex/MAB-3) domain transcription factor necessary for specific aspects of differentiation in sex-specific tissues of the male. mab-23 is required for the patterning of posterior sensory neurons in the male nervous system, sex muscle differentiation, and morphogenesis of the posterior hypodermis, spicules, and proctodeum. Failure of mab-23 mutant males to sire progeny is due primarily to defective sex muscle-mediated turning during copulatory behavior and likely compounded by impairment of sperm passage through the proctodeum. In the male nervous system, mab-23 refines ray neuron subtype distribution by restricting expression of dopaminergic neurotransmitter identity through interactions with the Hox gene egl-5 and a TGF-β-related signaling pathway. mab-23 has distinct roles and functions independent of mab-3, indicating different aspects of C. elegans male sexual differentiation are coordinated among DM domain family members. Our results support the hypothesis that DM domain genes derive from an ancestral male sexual regulator and suggest how regulation of sexual development has evolved in distinct ways in different phyla

Polycomb-like genes are necessary for specification of dopaminergic and serotonergic neurons in Caenorhabditis elegans

The molecular mechanisms underlying the formation of neurons with defined neurotransmitters are not well understood. In this study, we demonstrate that the PcG-like genes in Caenorhabditis elegans, sop-2 and sor-3, regulate the formation of dopaminergic and serotonergic neurons and several other neuronal properties. sor-3 encodes a novel protein containing an MBT repeat, a domain that contains histone-binding activity and is present in PcG proteins SCM and Sfmbt in other organisms. We further show that mutations in sor-3 lead to ectopic expression of Hox genes and cause homeotic transformations. Specification of certain neuronal identities by these PcG-like genes appears to involve regulation of non-Hox gene targets. Our studies revealed that the PcG-like genes are crucial for coordinately regulating the expression of discrete aspects of neuronal identities in C. elegans

The <i>C. elegans</i> Male Exercises Directional Control during Mating through Cholinergic Regulation of Sex-Shared Command Interneurons

<div><p>Background</p><p>Mating behaviors in simple invertebrate model organisms represent tractable paradigms for understanding the neural bases of sex-specific behaviors, decision-making and sensorimotor integration. However, there are few examples where such neural circuits have been defined at high resolution or interrogated.</p><p>Methodology/Principal Findings</p><p>Here we exploit the simplicity of the nematode <i>Caenorhabditis elegans</i> to define the neural circuits underlying the male’s decision to initiate mating in response to contact with a mate. Mate contact is sensed by male-specific sensilla of the tail, the rays, which subsequently induce and guide a contact-based search of the hermaphrodite’s surface for the vulva (the vulva search). Atypically, search locomotion has a backward directional bias so its implementation requires overcoming an intrinsic bias for forward movement, set by activity of the sex-shared locomotory system. Using optogenetics, cell-specific ablation- and mutant behavioral analyses, we show that the male makes this shift by manipulating the activity of command cells within this sex-shared locomotory system. The rays control the command interneurons through the male-specific, decision-making interneuron PVY and its auxiliary cell PVX. Unlike many sex-shared pathways, PVY/PVX regulate the command cells via cholinergic, rather than glutamatergic transmission, a feature that likely contributes to response specificity and coordinates directional movement with other cholinergic-dependent motor behaviors of the mating sequence. PVY/PVX preferentially activate the backward, and not forward, command cells because of a bias in synaptic inputs and the distribution of key cholinergic receptors (encoded by the genes <i>acr-18, acr-16</i> and <i>unc-29</i>) in favor of the backward command cells.</p><p>Conclusion/Significance</p><p>Our interrogation of male neural circuits reveals that a sex-specific response to the opposite sex is conferred by a male-specific pathway that renders subordinate, sex-shared motor programs responsive to mate cues. Circuit modifications of these types may make prominent contributions to natural variations in behavior that ultimately bring about speciation.</p></div

Male mating behavior is characterized by distinct patterns of locomotion.

<p>A cartoon depicting the key changes observed in male movement and body posture that are triggered by mate contact. <b><i>A.</i></b> In the absence of mate contact, male locomotion resembles that of the hermaphrodite: the male moves with a forward locomotion bias and the sinusoidal body wave driving movement propagates along the full length of the body. <b><i>B.</i></b> Contact with a mate via the male tail induces contact response: the male presses his tail against the hermaphrodite surface and commences backward movement. <b><i>C.</i></b> Backward locomotion continues until the vulva is sensed, whereupon the male pauses and prods for the vulva slit opening with his copulatory spicules. The male sensory rays (shown in the inset for <i>B</i>), which sense hermaphrodite contact, are essential for the induction and maintenance of tail apposition and for directional control on the hermaphrodite surface.</p

Optogenetic manipulation of PVY and PVX activity affects male movement.

<p><b><i>A, B.</i></b> PVY and PVX artificial stimulation, using ChR2, induces backward locomotion that is male-specific and depends on sex-shared locomotory system cells. The graphs show the impact of ChR2 activation on <i>Pnlp-14::ChR2-YFP</i> transgenic animal locomotion. Except for H (hermaphrodites) in <i>(A)</i>, all animals tested were transgenic males (in <i>(A),</i> male treatments are designated “M”). Except for the “-ATR M” control treatment in <i>(A)</i>, all animals were cultured and assayed in the presence of OP50 <i>E.coli</i> food supplemented with ATR. The X-axis indicates the food supplementation conditions (+ATR or –ATR), animal sex or which cells were ablated. The controls in <i>(B)</i> correspond to mock-ablated animals. The Y-axis shows the distance traveled (in µm) in response to the flash, with the negative values indicating backward (BK) movement and the positive values indicating forward (FWD) movement (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060597#s4" target="_blank">Materials and Methods</a>). Statistical comparisons to the relevant controls were made using a ranksum test for differences in the median. Tabled below each graph is the percentage of animals in each treatment that backed, paused or continued to move forward (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060597#s4" target="_blank">Materials and Methods</a> for the µm range of each category). <i>n</i> is the number of worms assayed in each treatment. <b><i>C</i></b><b>.</b> Artificial hyperpolarization of PVY and PVX blocks backing in the context of mating. Shown is the pausing frequency of <i>Pnlp-14::NpHR-EYFP</i> males in response to yellow light flashes. The X-axis shows the food supplementation and mating (Mating or Not Mating) conditions used. The Y-axis indicates the percentage of light flashes (out of 5) that induced pausing. <i>n</i>: -ATR Mating, 26; +ATR Mating, 28; -ATR Not Mating, 10; +ATR Not Mating, 10. Comparisons between –ATR and +ATR treatments were made using a ranksum test. Significance, *p<0.05; **p<0.005.</p

Male movement during mating depends on sex-shared and male-specific interneurons.

<p><b><i>A.</i></b> Schematic of an adult male (lateral view, left side) showing the anatomical location of cells ablated in experiments shown in <i>B–D</i> and in Fig. 3. Sex-shared cells (pink); male-specific cells (blue). The backward command interneurons (only the left AVA neuron is shown) have cell bodies in the head and send a process along the ventral nerve cord (VNC) where they synapse with motor neurons required for locomotion (the distribution of cell bodies for only a single motor neuron class is shown). PVY and PVX (located in the male pre-anal ganglion) receive inputs from the ray sensory neurons and have outputs onto the command interneuron processes. <b><i>B–D.</i></b> The impact of cell-specific ablations on three aspects of vulva search behavior related to locomotory control. <b><i>B</i></b><b>.</b> Contact response efficiency. <b><i>C.</i></b> Scanning speed. <b><i>D.</i></b> The number of times tail contact was lost per mating. The X-axis indicates the cells ablated in each treatment. A box plot representation of the data is shown, with median and mean values indicated by the line and the black dot within the box, respectively. Comparisons to the control (mock-ablated) were made using a ranksum test. The number of males assayed for each treatment, n: Control = 63; -PVY-PVX = 15; -PVY = 19; -PVX = 8; -AVA = 22. Significance, *p<0.05; **p<0.005.</p