Recruitment of transcription complexes to the beta-globin gene locus in vivo and in vitro.

Erythroid-specific, high level expression of the beta-globin genes is regulated by the locus control region (LCR), composed of multiple DNase I-hypersensitive sites and located far upstream of the genes. Recent studies have shown that LCR core elements recruit RNA polymerase II (pol II). In the present study we demonstrate the following: 1) pol II and other basal transcription factors are recruited to LCR core hypersensitive elements; 2) pol II dissociates from and re-associates with the globin gene locus during replication; 3) pol II interacts with the LCR but not with the beta-globin gene prior to erythroid differentiation in embryonic stem cells; and 4) the erythroid transcription factor NF-E2 facilitates the transfer of pol II from immobilized LCR constructs to a beta-globin gene in vitro. The data are consistent with the hypothesis that the LCR serves as the primary attachment site for the recruitment of macromolecular complexes involved in chromatin structure alterations and transcription of the globin genes.

Developmental expression of mouse muscleblind genes Mbnl1, Mbnl2 and Mbnl3.

The RNA-mediated pathogenesis model for the myotonic dystrophies DM1 and DM2 proposes that mutant transcripts from the affected genes sequester a family of double-stranded RNA-binding factors, the muscleblind proteins MBNL1, MBNL2 and MBNL3, in the nucleus. These proteins are homologues of the Drosophila muscleblind proteins that are required for the terminal differentiation of muscle and photoreceptor tissues, and thus nuclear sequestration of the human proteins might impair their normal function in muscle and eye development and maintenance. To examine this model further, we analyzed the expression pattern of the mouse Mbnl1, Mbnl2, and Mbnl3 genes during embryonic development and compared muscleblind gene expression to Dmpk since the RNA pathogenesis model for DM1 requires the coordinate synthesis of mutant Dmpk transcripts and muscleblind proteins. Our studies reveal a striking overlap between the expression of Dmpk and the muscleblind genes during development of the limbs, nervous system and various muscles, including the diaphragm and tongue.