Identification and functional characterization of a primate-specific E2F1 binding motif regulating MCPH1 expression.

MCPH1 (also named BRIT1) is one of the known genes responsible for autosomal recessive primary microcephaly (small head syndrome), suggesting its important role in brain development. The interaction of MCPH1 with transcriptional factors like E2F1 is required for the activation of cell cycle checkpoint, DNA repair and apoptosis. However, the molecular mechanism of MCPH1 regulation is currently unclear. Here, we cloned the human MCPH1 promoter and we identified a novel E2F1 binding motif located in the proximal promoter region of MCPH1. The experiments using electrophoretic mobility shift and promoter assays showed that E2F1 could stimulate MCPH1 transcription by direct binding to the E2F1 motif. Overexpression of E2F1 led to the upregulation of MCPH1 transcription, and knocking down the endogenous E2F1 resulted in the inhibition of the MCPH1 promoter activity. Surprisingly, sequence comparison of vertebrate species suggested that the identified E2F1 binding motif is primate specific, consistent with the previous observation of rapid evolution of MCPH1 protein sequence in primates. We propose that during primate evolution MCPH1 has acquired a novel E2F1 binding motif in its promoter which may act as a parallel mechanism, acting together with the rapid protein sequence changes in primates, and eventually contributed to brain enlargement during primate evolution and human origin. Database The MCPH1 promoter region was sequenced in human, chimpanzee and rhesus macaque. Nucleotide sequence data are available in the GenBank database (http://www.ncbi.nlm.nih.gov/genbank/) under accession numbers JN573214, JN573215 and JN573216.