The expression of the avian clusterin gene can be driven by two alternative promoters with distinct regulatory elements.

Clusterin cDNA has been isolated as a copy of a mRNA overexpressed in a wide variety of biological disorders, including tissue regression, brain injuries and oncogenic cell transformation. While the molecular cloning of the rat and the human clusterin genes has revealed a high degree of conservation of the genomic organization between mammals, the avian locus described here illustrates several divergent features. The avian gene has the particularity to be transcribed from at least two different promoters, both of which are active in transient expression assays using the quail QT6 transformed cell line. The detection of the two clusterin mRNA species by reverse-transcription-mediated PCR reveals a coordinated initiation of transcription from both promoters in all organs tested. In possible relation to the bipartite organization of the avian regulatory region, the putative cis-elements described in the unique mammalian promoters appear divided among the two avian promoters. In addition, the sequence comparison of avian and mammalian regulatory sequences has allowed the identification of a conserved putative cis-element which appears to be the target for specific DNA-binding factors.