Fish Physiology and Biochemistry 25: 231–238, 2001. © 2002 Kluwer Academic Publishers. Printed in the Netherlands. 231 Characterization of two molecular forms of vasoactive intestinal polypeptide (VIP) from the pallid sturgeon, Scaphirhynchus albus (Acipenseriformes) J.B. Kim 1 , B.A. Barton 2 and J.M. Conlon 1,3,∗ 1 Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, NE 68178, USA; 2 Department of Biology, University of South Dakota, Vermillion, SD 57069, USA; 3 Department of Biochemistry, Faculty of Medicine and Health Sciences, United Arab Emirates University, PO Box 17666, Al Ain, United Arab Emirates; ∗ Author for correspondence (Phone: 971-3-7039484; Fax: 971-3-7672033; E-mail: jmconlon@uaeu.ac.ae) Accepted: October 4, 2002 Key words: Acipenseridae, polyploidy, phylogeny, Scaphirhynchinae, structure-activity, tetraploidization Abstract Vasoactive intestinal polypeptide (VIP) was isolated in two molecular forms from an extract of the gastroenteropan- creatic system of the pallid sturgeon Scaphirhynchus albus (Acipenseriformes). VIP-1 was identical to the peptide previously isolated from the rainbow trout Oncorhynchus mykiss and the bowfin, Amia calva, consistent with the proposed sister group relationship of the Acipenseriformes and the Neopterygii. Sturgeon VIP-2 contained the amino acid substitution (Ala 4 → Ser) at a site previously regarded as invariant. The isolation of two distinct VIP gene products provides some support for the hypothesis that S. albus, with approximately 120 chromosomes, is functionally tetraploid but the alternative view that the species is functionally diploid and the two peptides arose from a local duplication of the VIP gene within the Scaphirhynchus lineage cannot be rejected. Introduction The Acipenseriformes are members of an extant order of ancient Actinopterygian (ray-finned) fishes com- prising the Acipenseridae (approximately 25 species of sturgeons) and Polyodontidae (two species of pad- dlefish). The family Acipenseridae is divided into four extant genera: Huso, Acipenser, Scaphirhynchus and Pseudoscaphirhynchus (Grande and Bemis 1991, 1996). Earlier cladistic analyses suggested that Scaphirhynchus and Pseudoscaphirhynchus constitute a monophyletic lineage (Scaphirhynchinae) that is sis- ter taxon to the subfamily Acipenserinae comprising the genus Acipenser in which the two species of the genus Huso are embedded (Bemis et al. 1997; Birstein and DeSalle 1998). However, more recent work based upon the nucleotide sequence of five mitochondr- ial genes suggests that Pseudoscaphirhynchus is also embedded within Acipenser (Birstein et al. 2002) It has been asserted that the genus Scaphirhynchus is the most basal lineage within the Acipenseridae and that divergence of the family occured in the middle to late Jurassic period (175 – 135 millions of years b.p.) (Birstein and DeSalle 1998; Krieger et al. 2000; Birstein et al. 2002). As well as representing a commercially important food source and a cause of concern to conservationists, the sturgeons constitute a ‘natural laboratory’ in which to study the processes of genome duplication, chromo- somal rearrangement, gene duplication and gene si- lencing. Although assigment of chromosome number can be somewhat imprecise (Ludwig et al. 2001), the Acipenseriformes may be divided into three classes: (a) species with approximately 120 chromosomes (range 110–130), (b) species with approximately 250 chromosomes (range 220–276), and (c) species with approximately 500 chromosomes (Birstein et al. 1997; Ludwig et al. 2001). Interpretation of these data is