823C Poster - 13. Neural development and physiology
Saturday April 09, 1:30 PM - 3:30 PM

Authors:
Priscilla Valentino ^1,2; Ted Erclik ^1,2

Affiliations:
1) University of Toronto, Toronto, Ontario, Canada; 2) University of Toronto: Mississauga, Mississauga, Ontario, Canada

Keywords:
d. neuronal specification; o. stem cells

In the Drosophila visual system, photoreceptors in the compound eye project visual information to neurons in the underlying optic lobe for processing. The largest neuropil of the optic lobe is the medulla, which mediates motion and colour processing, and is comprised of over 90 cell types. The medulla develops from a larval crescent of neuroepithelial (NE) cells termed the outer proliferation centre (OPC). In the 3^rd instar larva, the NE cells of the OPC are converted into neuroblasts, which then asymmetrically divide to generate the 90 types of medulla neurons. Previous studies have shown that two axes of positional information are required for neuronal specification. In the temporal axis, 5 transcription factors are sequentially expressed in the medulla neuroblasts as they age. In the spatial axis, the OPC is patterned into 5 spatial compartments by the non-overlapping expression of 3 homeobox transcription factors; Vsx1 in the center of the crescent, Optix in the adjacent arms and Rx in the tips. Thus, distinct neuronal types can be assigned unique spatio-temporal birth addresses based on the spatial compartment and temporal window from which they were born. Surprisingly, it has also been observed that neurons with identical spatio-temporal birth addresses can assume different fates based on whether they are born in the dorsal or ventral half of the OPC, suggesting that the dorsal and ventral halves of the OPC crescent are also spatially patterned. Here, using a technique involving micropipette-based cell isolation and RNA-seq, we identify 4 transcription factors that are differentially expressed in the dorsal and ventral halves of the OPC NE; salm and salr are expressed in all dorsal OPC cells, whereas disco and disco-r are expressed in all ventral cells. We show that the expression patterns of these genes meet to form a sharp dorsal-ventral boundary in the Vsx1 region of the OPC. We further demonstrate that salm/salr and disco/disco-r negatively cross-regulate each other in the OPC NE to maintain this dorsal-ventral compartment boundary. Loss- and gain-of-function experiments are currently underway to determine whether these genes contribute to medulla neuronal specification. It is anticipated that investigating the neurogenic role of these genes in the medulla will further our understanding of how neural diversity is generated at the intersection of temporal and spatial inputs.