850C Poster - 13. Neural development and physiology
Saturday April 09, 1:30 PM - 3:30 PM

Authors:
Khaled Ben el kadhi ¹; Claude Desplan ^1,2

Affiliations:
1) New York University Abu Dhabi, Abu Dhabi, UAE; 2) New York University, NY, USA

Keywords:
o. stem cells; c. neural stem cells

The Drosophila compound eye is composed of 800 unit eyes; each contains 8 photoreceptors (PRs). The visual information collected by the PRs is transferred to the 4 visual processing centers of the optic lobe, the lamina, medulla, lobula and lobula plate. The medulla is the most complex structure of the optical lobe, it consists of 40,000 neurons. These neurons are the progeny of 800 medulla NeuroBlasts (NBs) that derive from a larval neuroepithelium, the Outer Proliferation Center (OPC). The OPC's NBs divide asymmetrically to self-renew and to produce a Ganglion Mother Cell (GMC) that will produce two different medulla neurons. It was shown that the sequential expression of 6 temporal transcription factors (tTF) (Hth-Klu-Ey-Slp-D-Tll) in NBs generates neuronal diversity. Although the tTF cascade was identified, we do not have dynamic information about the timing mechanisms, the duration of each temporal identity and how the transition occurs between tTFs.
The general aim of my work is to develop a NBs primary culture to define the molecular clock of the tTF cascade using live-imaging (L-I).
We used the CRISPR-Cas9 system to endogenously tag the tTFs with different fluorescent proteins and/or transcriptional reporters MS2 or PP7. Using L-I we quantified the duration of multiple competence windows, the number of cell divisions as well as the duration of the transitions. To test if the molecular clock of the tTFs cascade is intrinsic to the NB. we set a quasi-isolated NB culture (qiNBc). We found that the transition between tTFs is maintained in qiNBc, suggesting that the transition signal is intrinsic to NB or comes from its progeny. We tested this hypothesis by selectively destructing the GMC or neurons (N) using Laser microablation techniques.
Obtaining these dynamic data will allow us to decipher the molecular clock of tTFs and provide essential information about the mechanisms responsible for the neuronal diversity in the Drosophila optic lobe, which will likely also apply to temporal patterning observed in mammals. More importantly, this will also enable us to understand how to program a naive neural stem cell to produce a specific type of neuron that could be used for cell replacement therapy.