The mouse beta B1-crystallin promoter: strict regulation of lens fiber cell specificity

Previous studies have shown that the chicken beta B1-crystallin promoter (- 434/+30) contains all of the signals necessary to specifically direct high level expression of heterologous genes to the lens fiber cells of mice. In the present study, the mouse beta B1-crystallin gene was cloned, and its re gulation was investigated to further elucidate the mechanisms controlling l ens fiber cell-specific gene expression. Phylogenetic footprinting analysis of the 5' flanking sequence from the mouse, rat, human and chicken beta B1 -crystallin genes identified several known and putative functional cis elem ents including the PL2 element which is required for lens-specific expressi on of the chicken PBI promoter. Surprisingly, however, all six mouse beta B 1-crystallin/CAT constructs tested (-1493/+43, - 1493/+30, -870/+30, -250/30, -1351+30 and -98/+30) were inactive in three different mammalian lens-d erived cell lines while only the -870/+30 and -98/+30 constructs were activ e in chicken primary patched lens epithelial cells. In contrast, the chicke n beta B1-crystallin promoter (-434/+30) was transcriptionally active in al l lens-derived cells tested. Transgenic mice harboring a mouse beta B1-crys tallin -1493/+44 CAT construct did express the transgene specifically in le ns fiber cells, however, at lower levels than that previously reported for a chicken -434/+30 CAT construct. These data suggest that, as in other crys tallin genes, the regulatory signals controlling lens fiber cell-specific e xpression are conserved between chicken and mouse. However, the inability o f the mouse beta B1-crystallin promoter to function in mammalian lens-deriv ed cultured cells implies that this gene has acquired additional cis-regula tory elements to ensure lens fiber cell specificity. (C) 2001 Elsevier Scie nce B.V. All rights reserved.