Identification of Rat Brahma (rBRM), a Subunit of SWI/SNF Chromatin Remodeling Complex: Involvement in the Differentiation of Retinal Stem Cells/Progenitors

Abstract

Abstract: : Purpose: The specification of retinal cell types requires a coordinated expression of a number of developmentally regulated transcription factors that influence the expression of phenotype specific genes. To understand the underlying mechanism of differentiation we carried out microarray analysis of global gene expression in retinal progenitors during proliferation and differentiation. The analysis led to the identification of an EST sequence (AA875609) that showed homology to human hBRM (SNF2α), a component of SWI/SNF chromatin remodeling complex. In Drosophila, BRM acts as an upstream activator of multiple homeotic genes during development and plays a role in transcriptional activation. In this study we wanted to investigate the role of rBRM gene in retinal development. Methods: Microarray analysis of transcripts expressed in E14 and E18 retinal stem cells/progenitors in proliferation and differentiation conditions was carried out using Affimetrix rat U34A array. Out of 22 EST; AA875609 was picked for further analysis due to its homology to hBRM (SNF2α) and correspondence of its transcript level with the differentiation of retinal progenitors. The full-length rBRM cDNA was cloned by RACE, cloned into pCR II vector and sequenced. Expression of rBRM during retinal development was analyzed by RT-PCR, In situ hybridization and immunocytochemistry analysis. Results: Swiss-Prot analysis of the deduced rBRM amino acid sequence showed 90% homology to hBRM and the presence of a conserved bromodomain region, spanning amino acid 128-185. The exact function of bromodomain region is not yet known but it is thought to be involved in protein-protein interactions for the assembly or activity of multicomponent complexes involved in transcriptional activation. The levels of transcript corresponding to rBRM increased in cultured stem cells/progenitors in differentiation condition. In vivo analysis of rBRM transcripts showed that it is first detected in E14 retina and increases as development progresses. Conclusions: The association of rBRM transcripts with differentiation in vivo and in vitro suggests that rBRM may play an important role in retinal cell specification, probably by recruiting developmentally regulated transcription factors for the activation of phenotype specific genes.

Keywords: retinal development • transcription • gene/expression