Comparative analysis of Delta-like 1 regulatory elements during brain development and evolution using transgenic mice.

LÓPEZ-LEAL RODRIGO; KAMM GRETEL B.; RUBINSTEIN MARCELO; FRANCHINI LF

Congreso; VI International Meeting of the Latin American Society for Developmental Biology; 2012

The gene Delta-like 1 (Dll1) has been implicated in the proliferation/differentiation switch of neural precursors during brain development. Dll1 encodes a ligand of Notch1 that inhibits neuronal precursors differentiation allowing them to proliferate increasing the undifferentiated progenitor pool. The expression of Dll1 is thighly controlled during brain development but the regions and mechanisms controlling its expression are not completely known. Previous works have shown that a region located 4.3 kb upstream of Dll1 (4.3-Dll1) drives the expression of the reporter gene lacZ in a subdomain of the endogenous expression pattern. In additon, in our laboratory we have identified an additional region located at 5.9 kb of Dll1 (5.9-Dll1) that controls the expression of a reporter gene in an overlapping manner to the endogenous gene pattern. Using transgenic mice expressing reporter genes under the control of 4.3-Dll1 and/or 5.9-Dll1 we have performed a detailed temporo-spatial study of coexpression and colocalization during mouse development in order to identify the unique properties of each regulatory region. In addition, we have found that the enhancer 5.9-Dll1 underwent lineage-specific evolution in the lineage leading to primates acquiring 6 primate specific substitutions in the central region of the enhancer that is otherwise very well conserved in all vertebrates. We found that swapping the six primate-specific nucleotides into the mouse enhancer expanded the spatio-temporal expression domain of a reporter gene in the developing neocortex between embryonic day (E)14.5 to E16.5 and at postnatal day 1. Moreover, swapping the ancestral nucleotides back into the human ortholog impaired enhancer function within the nervous system beyond E14.5 indicating that these substitutions could be critical for proper DLL1 expression at later stages of brain development. We propose that a spatio-temporal switch of DLL1 expression driven by these six primate-specific substitutions could have contributed to increase the number of neural precursors in the telencephalon and, ultimately, to shape the enlarged primate brain. Our data brings new information into the understanding of the regulation of Dll1 expression during brain development and evolution.