Expression of the murine alpha B-crystallin gene in lens and skeletal muscle: identification of a muscle-preferred enhancer.

Abstract

The aB-crystallin gene is expressed at high levels in lens and at lower levels in some other tissues, notably skeletal and cardiac muscle, kidney, lung, and brain. A promoter fragment of the murine aeB-crystallin gene extending from positions -661 to +44 and linked to the bacterial chloramphenicol acetyltransferase (CAT) gene showed preferential expression in lens and skeletal muscle in transgenic mice. Transfection experiments revealed that a region between positions -426 and -257 is absolutely required for expression in C2C12 and G8 myotubes, while sequences downstream from position -115 appear to be determinants for lens expression. In association with a heterologous promoter, a -427 to -259 fragment functions as a strong enhancer in C2C12 myotubes and less efficiently in myoblasts and lens. Gel shift and methylation interference studies demonstrated that nuclear proteins from C2C12 myoblasts and myotubes specifically bind to the enhancer.Crystallins comprise approximately 90% of the watersoluble proteins of the transparent eye lens and are important for its optical properties (52, 53). The three dominant classes of mammalian crystallins (a, P, and -y) contain two or more related polypeptides ranging in size from approximately 20 to 30 kDa and display regulated spatial and temporal expression within the lens (38, 52). Additional crystallins, the taxon-specific crystallins, exhibit a more restricted phylogenetic distribution; they are closely related or identical to common metabolic enzymes and are expressed at low concentrations outside the lens (11, 39).The two a-crystallin proteins, axA and aB, have been the subject of extensive structural, biophysical, and evolutionary studies. aA-and aB-crystallin share approximately 55% sequence identity at the amino acid level (49), and mammalian ot-crystallin genes exhibit conservation at the level of gene structure (12,22,42,48). aA-and aB-crystallin are distantly related to an egg antigen of Schistosoma mansoni (35) and the small heat shock proteins of Drosophila melanogaster (19), and both the a-crystallins and small heat shock proteins are found associated with high-molecularweight aggregates and may be phosphorylated (30). The two a-crystallin genes presumably arose from a gene duplication event, originating from an ancestor of a small heat shock gene.Despite these similarities, the two a-crystallin genes are expressed differently. The oxA-crystallin gene is expressed only in the lens (13,37,50). In contrast, the aB-crystallin gene, while expressed abundantly in lens, is also expressed at reduced levels in a variety of other tissues, including heart, skeletal muscle, kidney, lung, brain, retina, and iris (3,13,20,21). aB-crystallin expression has been associated with a variety of pathological and experimental conditions, notably Alexander's disease (21) and Lewy body disease (31) in humans, scrapie infection in hamsters (14) (50). Moreover, the murine aA-crystallin promoter contains an element between positions -66 to -57 which binds a zinc finger protein homologo...

Adaptive evolution of small heat shock protein/ αB-crystallin promoter activity of the blind subterranean mole rat,Spalax ehrenbergi

“…As expected (18,32), the highest average values for mouse shsp͞␣B-crystallin promoter activity were in the lens, heart, and skeletal muscle (gracius leg muscle) of the transgenic mice (Fig. 4a).…”

Sumoylation activates the transcriptional activity of Pax-6, an important transcription factor for eye and brain development

“…Therefore, we tested the transcriptional activities of these two isoforms on the αB-crystallin promoter (−427 to +44) containing four copies of Pax-6 binding sites (22). As shown in Fig.…”

Muscle Develops a Specific Form of Small Heat Shock Protein Complex Composed of MKBP/HSPB2 and HSPB3 during Myogenic Differentiation

“…Functional Divergence of the Two sHSP Systems in Muscle Cells-Several studies have demonstrated that the expression of ␣B-crystallin is regulated during skeletal and cardiac muscle development, and that its chaperone-like functions are also coupled to the activation of genetic programs responsible for myogenic differentiation and cardiac morphogenesis (47,48). Here, using a mouse myoblast cell line, C2C12, as well as 10TflagMyoD cells, which stably transform to myoblasts, we demonstrated the up-regulation of ␣B-crystallin expression during the very early stages of myogenic differentiation.…”