Ghanem, A.M.; (2010) Molecular regulation of Sox2 expression during differentiation of chick embryonic stem cells. Doctoral thesis , UCL (University College London).

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Abstract

The transcription factor Sox2 has a key role not only in maintaining stem state but also in specification of neural fate of embryonic cells. Multiple regulatory elements have been identified in the Sox2 locus (Uchikawa et al, 2003). In the developing embryo, these regulatory elements are activated differentially in time and space. We studied the activity of 25 defined regulatory elements of the Sox2 promoter in three different lines of chick ES cells. By transfection of plasmids encoding Enhanced Green Fluorescent Protein (EGFP) and the minimal promoter thymidine kinase (tk) coupled with individual Sox2 regulatory elements we find that the Sox2 enhancer N2 has the highest activity in proliferating chick cell lines compared with other enhancer regions. Under conditions that induce ES cells to differentiate into neurons the activity of the N2 enhancer increased along with an increase in levels of expression of Sox2 mRNA. Further analysis of the N2 enhancer sequence identified two subregions with 176 and 73 base pairs (bp) which are highly conserved between chick, mouse and man. Functional studies performed with the tk-EGFP reporter plasmids under the control of five regulatory sequences containing the mouse N2 enhancer in its full length, its two sub-regions (176 and 73 bp) or sequences composed of the full length of the mouse N2 from which each of the two sub-regions 176 bp and 73 bp has been deleted confirmed that the two sub-regions of the N2 enhancer account for its activity in both proliferating cES cells as well as their induced neural differentiation state. These findings suggest that N2 core regulatory regions encode conserved instructions required to direct expression of Sox2 both in embryonic stem cells induced to neural differentiation and in the neural plate of the embryo itself.

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