Rhonda Hyde et al. (2003) International Worm Meeting "Identifying candidate genes involved in serotonin modulation of a C. elegans behavioral circuit"

Rhonda Hyde, Pierre-Olivier Barome, Anne C Hart, Laurent Segalat, Michael Y Chao

[International Worm Meeting, 2003]

In the nervous system, G-protein coupled receptors (GPCRs) mediate slow synaptic transmission through the activation of signaling cascades. GPCRs have been shown to alter synaptic transmission both presynaptically by affecting neurotransmitter release and postsynaptically by modulating receptor function and localization. Work in our lab has shown that avoidance of the chemical repellant 1-octanol is modulated by serotonin. Laser ablation experiments reveal that well-fed animals sense the presence of octanol through the ASH sensory neurons while octanol detection in starved animals involves ASH and two other pairs of sensory neurons, ADL and AWB (1). This food-dependent effect can be mimicked with exogenous serotonin, consistent with increased levels of serotonin in animals on food. These studies show that feeding status and endogenous serotonin levels are responsible for selective signaling by sensory neurons in octanol avoidance. We are interested in identifying the serotonin GPCRs that modulate octanol avoidance to determine the sites of action of serotonin in the avoidance circuit. There are 2 characterized C. elegans serotonin GPCRs, 5-HT-Ce (2) and 5-HT2-Ce (3). From a search of the C. elegans genome, we identified 10 additional receptors that share sequence similarity to the 5-HT-Ce receptor. Transcriptional fusion constructs will be used to determine the expression patterns of each receptor. Receptors that are expressed in either the sensory neurons or command interneurons are strong candidates for modulating the octanol avoidance response. RNAi will be used to determine their functional significance in avoidance behavior. A previous screen conducted by Hana Fukuto in the lab identified mutant strains with defective octanol responses off food but normal responses on food. Exogenous serotonin restores normal response to octanol in all but one strain. This mutant strain also has defects in other serotoninergic behaviors. We are mapping and further characterizing the corresponding gene to determine its role in serotonin signaling. References: (1) Chao et al ECWM 2002, IWM 2003 (2) Olde and McCombie J Mol Neurosci 1997 (3) Hamdan et al J. Neurochem 1999

Virginie Hachet et al. (2006) European Worm Meeting "Centrosomes Dictate Timing of Mitotic Entry in C. elegans Embryos"

Pierre Gonczy, Virginie Hachet

[European Worm Meeting, 2006]

Virginie Hachet and Pierre Gonczy Mitosis is a tightly regulated process that allows equal repartition of the genetic material to daughter cells. Activation of the Cyclin B1/Cdk1 complex is key for initiating entry into mitosis. Intriguingly, in human cells, the active form of Cyclin B1/Cdk1 is detected first at centrosomes, the major microtubule organizing centre (MTOC) of animal cells. However, it is not known in any systems whether centrosomes are required for promoting mitotic entry. We set out to investigate the mechanisms underlying timing of mitotic entry, in the early C. elegans embryo. To this end, we developed a novel assay to monitor timing of mitotic entry with high spatial and temporal resolution. Using this assay, we showed that neither anterior-posterior (A-P) polarity, nor microtubules, dictate timing of mitotic entry. By contrast, we established that centrosome integrity is essential. Moreover, we found that the centrosomal Aurora-A kinase AIR-1 is essential for proper mitotic timing. Finally, by using appropriate mutant embryos, we could demonstrate that centrosomes are not only necessary but also sufficient to promote entry into mitosis. Our findings lead us to propose that centrosomes serve as integrative centres for mitotic regulators and thus dictate the timing of mitotic entry.

Doroquez, D. B. et al. (2009) International Worm Meeting "The Role of Intracellular Trafficking in Modulating Ciliary Structure and Function in C. elegans."

Olivier-Mason, A., Yates III, J. R., Sengupta, P., Doroquez, D. B., Sarkeshik, A.

[International Worm Meeting, 2009]

Primary cilia are organelles that serve as environmental sensors, and are present on nearly all cell types in vertebrates. Each cilium consists of a central microtubular axoneme surrounded by a membrane. The structure and biogenesis of these organelles are highly conserved from algae to humans, allowing for parallel studies of cilia in many model systems. Defects in cilia biology are implicated in multiple diseases, including polycystic kidney disease, Bardet-Biedl syndrome and sensory pathologies. C. elegans is an ideal system to study cilia with its experimental tractability and the ability to analyze its 60 ciliated sensory neurons. These cilia are essential for sensory functions, such as chemosensation and olfaction. Individual olfactory neurons exhibit highly specialized cilia structures that are essential for their unique sensory functions. Cell-specific mechanisms of intraflagellar transport (IFT) and sensory signaling contribute to ciliary structural and morphological diversity. In particular, sensory signaling is required to modulate the specialized architecture of AWB olfactory neuron cilia and this modulation is dependent on vesicular trafficking. Little is known about the regulation of vesicular trafficking in cilia formation and maintenance. Defects in trafficking are likely to affect cilia structure and function due to altered transport and localization of ciliary signaling molecules resulting in defective cellular homeostasis. The overall goal of this project is to study the role of intracellular trafficking in the generation and maintenance of cilia morphology in C. elegans. In order to identify components involved in C. elegans cilia biology, we have taken a proteomics-based approach. We have identified proteins associated with different IFT complex proteins and motors via mass spectrometry. Many predicted IFT-associated components were identified in this analysis, suggesting that this approach may allow us to identify new cilia-related components [Olivier-Mason et al. abstract]. We have identified vesicular trafficking proteins associated with IFT complex proteins. We are characterizing the roles of identified vesicular trafficking proteins in the regulation of cell-specific cilia biogenesis, the localization of ciliary transmembrane proteins, and the maintenance of sensory signaling. These experiments will elucidate the role of vesicular transport in the regulation of cilia structure, and provide new information about how these sensory organelles are built and maintained. These studies may provide insights into the basic biology underlying ciliopathies.