Neuropeptide signalling shapes feeding and reproductive behaviours in male C. elegans

Sexual dimorphism occurs where different sexes of the same species display differences in characteristics not limited to reproduction. For the nematode Caenorhabditis elegans, in which the complete neuroanatomy has been solved for both hermaphrodites and males, sexually dimorphic features have been observed both in terms of the number of neurons and in synaptic connectivity. In addition, male behaviours, such as food-leaving to prioritise searching for mates, have been attributed to neuropeptides released from sex-shared or sex-specific neurons. In this study, we show that the lury-1 neuropeptide gene shows a sexually dimorphic expression pattern; being expressed in pharyngeal neurons in both sexes but displaying additional expression in tail neurons only in the male. We also show that lury-1 mutant animals show sex differences in feeding behaviours, with pharyngeal pumping elevated in hermaphrodites but reduced in males. LURY-1 also modulates male mating efficiency, influencing motor events during contact with a hermaphrodite. Our findings indicate sex-specific roles of this peptide in feeding and reproduction in C. elegans, providing further insight into neuromodulatory control of sexually dimorphic behaviours.

Anisotropy of plasmalemmal sterols and cell mating require StARkin domain proteins Ysp2 and Lam4

In the budding yeast S. cerevisiae Cdc42 is required for polarized growth and the formation of mating projections (shmoos). Negatively charged lipids including phosphatidylserine and phosphatidylinositol 4,5-bisphosphate support a positive feedback loop that recruits Cdc42 effectors and MAP kinase scaffolds, many of which contain polybasic patches that directly interact with the membrane. Here, using genetically encoded sterol sensor ALOD4 we find that ergosterol is accumulated in the cytosolic leaflet of buds and shmoos. The accumulation of ergosterol in the plasma membrane requires both Osh and Lam proteins however cells lacking Ysp2/Lam2 and Lam4 displayed a reversal in the polarity of ergosterol. The redistribution of ergosterol impairs the polarization of phosphatidylserine and phosphatidylinositol 4,5-bisphophate which further impacts shmoo formation, MAPK signaling and mating efficiency. Our observations demonstrate that the ability of Lam proteins to deliver ergosterol from the plasma membrane to the ER helps maintain a gradient of ergosterol which in turn supports robust cell polarity.SummaryThe sterol sensor ALOD4 is enriched at sites of polarized growth. Elimination of the Osh proteins solubilized the ALOD4 whereas elimination of Ysp2 and Lam4 reversed ALOD4 polarization. Cells lacking Ysp2 and Lam4 have defects in mating and MAP kinase signaling.

Kel1 is a phosphorylation-regulated noise suppressor of the pheromone signaling pathway

Mechanisms have evolved that allow cells to detect signals and generate an appropriate response. The accuracy of these responses relies on the ability of cells to discriminate between signal and noise. How cells filter noise in signaling pathways is not well understood. We have analyzed noise suppression in the yeast pheromone signaling pathway. By combining synthetic genetic array screening, mass spectrometry and single-cell time-resolved microscopy, we discovered that the poorly characterized protein Kel1 serves as a major noise suppressor of the pathway. At the molecular level, Kel1 suppresses spontaneous activation of the pheromone response by inhibiting membrane recruitment of Ste5 and Far1. Kel1 is regulated by phosphorylation, and only the hypophosphorylated form of Kel1 suppresses signaling, reduces noise and prevents pheromone-associated cell death. Our data indicate that in response to pheromone the MAPKs Fus3 and Kss1 phosphorylate Kel1 to relieve inhibition of the pheromone pathway. Taken together, Kel1 serves as a phospho-regulated suppressor of the pheromone pathway to reduce noise, inhibit spontaneous activation of the pathway, regulate mating efficiency and to prevent pheromone-associated cell death.

Phosphorylated Gβ is a directional cue during yeast gradient tracking

Budding yeast cells interpret shallow pheromone gradients from cells of the opposite mating type, polarize their growth toward the pheromone source, and fuse at the chemotropic growth site. We previously proposed a deterministic, gradient-sensing model that explains how yeast cells switch from the intrinsically positioned default polarity site (DS) to the gradient-aligned chemotropic site (CS) at the plasma membrane. Because phosphorylation of the mating-specific Gβ subunit is thought to be important for this process, we developed a biosensor that bound to phosphorylated but not unphosphorylated Gβ and monitored its spatiotemporal dynamics to test key predictions of our gradient-sensing model. In mating cells, the biosensor colocalized with both Gβ and receptor reporters at the DS and then tracked with them to the CS. The biosensor concentrated on the leading side of the tracking Gβ and receptor peaks and was the first to arrive and stop tracking at the CS. Our data showed that the concentrated localization of phosphorylated Gβ correlated with the tracking direction and final position of the G protein and receptor, consistent with the idea that gradient-regulated phosphorylation and dephosphorylation of Gβ contributes to gradient sensing. Cells expressing a nonphosphorylatable mutant form of Gβ exhibited defects in gradient tracking, orientation toward mating partners, and mating efficiency.

Pheromone Mediated Sexual Reproduction of Pennate Diatom Cylindrotheca closterium

Benthic diatoms dominate primary production in marine subtidal and intertidal environments. Their extraordinary species diversity and ecological success is thought to be linked with their predominantly heterothallic sexual reproduction. Little is known about pheromone involvement during mating of pennate diatoms. Here we describe pheromone guided mating in the coastal raphid diatom Cylindrotheca closterium. We show that the two mating types (mt+ and mt−) have distinct functions. Similar to other benthic diatoms, mt+ cells are searching for the mt− cells to pair. To enhance mating efficiency mt− exudes an attraction pheromone which we proved by establishing a novel capillary assay. Further, two more pheromones produced by mt− promote the sexual events. One arrests the cell cycle progression of mt+ while the other induces gametogenesis of mt+. We suggest that C. closterium shares a functionally similar pheromone system with other pennate diatoms like Seminavis robusta and Pseudostaurosira trainorii which synchronize sexual events and mate attraction. Remarkably, we found no evidence of mt+ producing pheromones, which differentiates C. closterium from other pennates and suggests a less complex pheromone system in C. closterium.

Pheromone Mediated Sexual Reproduction of Pennate Diatom Cylindrotheca Closterium

Benthic diatoms dominate primary production in marine subtidal and intertidal environments. Their extraordinary species diversity and ecological success is thought to be linked with their motility and predominantly heterothallic sexual reproduction. Little is known about pheromone involvement during mating of pennate diatoms. Here we describe pheromone guided mating in the coastal raphid diatom Cylindrotheca closterium. We show that the two mating types (mt+ and mt¯) have distinct functions. Similar to other benthic diatoms, mt+ cells are searching for the mt¯ cells to pair. To enhance mating efficiency mt¯ exudes an attraction pheromone, which we proved by establishing a novel capillary assay. Further, two more pheromones produced by mt¯ promote the sexual events. One arrests the cell cycle progression of mt+ while the other induces gametogenesis of mt+. We suggest that C. closterium shares a functionally similar pheromone system with other pennate diatoms like Seminavis robusta and Pseudostaurosira trainorii which synchronize sexual events and mate attraction. Remarkably, we found no evidence of mt+ producing pheromones, which differentiates C. closterium from other pennates and suggests a less complex pheromone system in C. closterium.

Deletion of ptn1, a PTEN/TEP1 Orthologue, in Ustilago maydis Reduces Pathogenicity and Teliospore Development

The PTEN/PI3K/mTOR signal transduction pathway is involved in the regulation of biological processes such as metabolism, cell growth, cell proliferation, and apoptosis. This pathway has been extensively studied in mammals, leading to the conclusion that PTEN is a major tumor suppressor gene. PTEN orthologues have been characterized in a variety of organisms, both vertebrates and non-vertebrates, and studies of the associated PTEN/PI3K/mTOR pathway indicate that it is widely conserved. Studies in fungal systems indicated a role of PTEN in fungal defense mechanisms in Candida albicans, and in the developmental process of sporulation in Saccharomyces cerevisiae. The present study was aimed at investigating the role of the PTEN ortholog, ptn1, in Ustilago maydis, the pathogen of maize. U. maydis ptn1 mutant strains where ptn1 gene is deleted or overexpressed were examined for phenotypes associate with mating, virulence and spore formation. While the overexpression of ptn1 had no substantial effects on virulence, ptn1 deletion strains showed slight reductions in mating efficiency and significant reductions in virulence; tumor formation on stem and/or leaves were severely reduced. Moreover, tumors, when present, had significantly lower levels of mature teliospores, and the percent germination of such spores was similarly reduced. Thus, ptn1 is required for these important aspects of virulence in this fungus.