We have continued to study the crystallin genes and their expression in the cellular eye lens. Experiments have provided evidence that the chicken and mouse alphaA-crystallin gene use different cis-acting sequences and trans-acting factors to regulate their expression. Partial purification of embryonic chicken lens nuclear proteins that bind to the mouse alphaA-crystallin promoter has been achieved. More importantly, it appears as if it will be possible to isolate these putative regulatory proteins and their cDNAs. In contrast to the alphaA-crystallin gene, which is highly lens-specific, the mouse alphaB-crystallin genes were shown to be expressed in numerous non-lens tissues (heart, kidney, skeletal muscle), although to a lesser extent than in lens. Experiments using cultured cells and transgenic mice indicated that regulation of the alpha beta gene resides in its 5' flanking sequence. The chicken beta1-crystallin promoter has been shown to be lens- specific in cultured cells; deletion mutants suggested the presence of a negative regulatory sequence (-436/-296) in this gene which may contribute to its tissue-specific expression. The concept of gene sharing was developed, which refers to the same gene encoding both a lens crystallin and a metabolic enzyme. Our data indicate that argininosuccinate lyase is encoded by the delta-crystallin genes (possibly only the delta2 gene in the chicken) and alpha- enolase by the single tau-crystallin gene in ducks and chickens. The tau-crystallin/alpha-enolase gene in ducks is expressed about 25 times more strongly in the lens than in the liver. Finally, sequences of tryptic peptides were obtained and an anti serum was raised to a synthetic peptide specific for a major crystallin (Jl) of the jellyfish eye lens. This initiates molecular studies on the crystallin of these ancient cellular lenses.
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