INC · Innate Neuronal Circuits

Innate Neuronal Circuits

Executive Summary: Sexual behaviours have the most fundamental importance to the animal and therefore it is not surprising that they represent a robust set of innate responses. Innate behaviours are ideal to study behaviour at the circuit level because they are likely hardwired and invariant from animal to animal. During courtship male and female flies perform gender specific behavior. We proposed to find the neurons involved in female receptivity because females integrate information about the male and her internal state and decide whether there will be copulation. We probed the circuit of female receptivity with two approaches: anatomical tracing and behavioural screening. A. Identification of neurons that receive input from courtship related projection neurons Studies of the connectivity of olfactory projection neurons within the fruitless expressing neurons show that at the third order neurons level there are male specific neurons. The questions we wanted to address were whether the fruitless expressing PNs connect to neurons that are not fruitless positive and whether we can identify other sexual dimorphisms within these third order neurons. Using photoactivatableGFP to activate the area of the axonal arbors of the projection neurons, we identified one set of neurons that becomes consistently activated and that is not fruitless positive. We saw other fruitless negative neurons light up but less consistently and with location that are harder to identify from one brain to the next. In this analysis we did not identify further sexual dimorphisms. We have established in the lab the 2-photon laser guided tracing of circuits that we are using also in other projects. B. Screen for behavioral mutants B.1 Small screen We did an inhibitory screen of 10 candidate enhancer-trap lines. We identified one positive line apterous-GAL4. We have characterized further the phenotype that results form the inhibition of apterous neurons. We observed that apterous does not label the sensory areas already known to be involved in receptivity and we confirmed that the effect is indeed neuronal. We confirmed that the females are courted by the males normally. We observed that the line although less receptive does not lay more eggs, therefore does not mimic the post-mating switch. We are using an intersectional approaches to find in detail which of the apterous positive neurons are involved in the phenotype. Once we finish these experiments we will write the manuscript B.2 Large screen: We tested 1042 lines from putative-enhancer-GAL4 collection of the Rubin lab. Initially, we screened for a fertility phenotype as it is a much faster process. We identified 75 lines in which at least 32% females tested did not produce progeny. We then tested receptivity in the lines that show a fertility defect. 25 lines have reduced receptivity. The 25 lines identified in the screen will be the basis for the projects in the lab in the following years.

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