The duck gene for α B-crystallin shows evolutionary conservation of discrete promoter elements but lacks heat and osmotic shock response

Abstract

The gene for α B-crystallin from a bird (the domestic duck, Anas platyrhynchos) has been cloned and sequenced to allow comparison with its mammalian homologues. The duck gene has the same general structure as those of humans and rodents although, unlike those of mammals, the duck gene has two polyadenylation signals at the 3′ end. The most interesting comparisons are in the 5′ flanking promoter regions. In contrast to the broad conservation of promoter sequence among mammals, only two significant blocks and a few smaller elements have been conserved during evolution in the more distantly related avian gene. Block 1 (−350/−308) corresponds to αBE-2, a functional element defined in the mouse gene. Further downstream, block 2 (−98/−65) shows 27 33 identity among all three species but does not correspond to any previously defined element. Other regions are less well-conserved. In particular, putative heat-shock response elements of the mammalian α B-crystallin genes are absent from the duck gene. In contrast to the heat and osmotic stress-inducibility of mouse α B-crystallin in NIH 3T3 cells, duck α B-crystallin showed no inducibility in duck cells in culture. Thus, although high expression in lens is common to α B-crystallin genes in birds and mammals, other modes of expression appear to be taxon-specific.