| The corpuscles of Stannius [CS], small perirenal endocrine glands implicated in calcium and phosphate regulation in bony fishes, show interspecific variation in number, anatomical distribution, and fine structure. Whereas the more ancient members of Neopterygii possess a large number of CS scattered throughout the kidney proper, the Euteleostei demonstrate a reduction in number and a more posterior and independent distribution of the glandular bodies with respect to the renal tissue. Stanniocalcin [STC], the only active principle characterized to date from the CS, appears to be more widely distributed among the vertebrates than was previously believed. Our examination into STC of the more ancient Actinopterygii suggests that this hormone has undergone considerable evolutionary pressure at the level of the molecule and in tissue distribution. Molecular approaches reveal differences in the protein core, the primary transcript size, and perhaps glycosylation of the STC molecule between species. Evidence at the molecular level suggests that STC mRNA may be subject to posttranslational processing and that tissue-specific expression of the STC gene is possible. This finding is interesting in light of the recent identification of STC in many mammalian tissues. Further, molecular approaches utilized to examine one member of the Osteoglossomorpha, one of the most ancient of teleosts, provide preliminary evidence that multiple forms of STC molecules may be present in representative species. Multiple sequence alignments of piscine STC revealed highly conserved structural elements found also in mammals. However, our results suggest that the variation in CS number, distribution, and fine structure, and differences in the STC molecule among Actinopterygii may be a consequence of their evolutionary history. |
