Ancestral genomic duplication of the insulin gene in tilapia: An analysis of possible implications for clinical islet xenotransplantation using donor islets from transgenic tilapia expressing a humanized insulin gene

Abstract

Tilapia, a teleost fish, have multiple large anatomically discrete islets which are easy to harvest, and when transplanted into diabetic murine recipients, provide normoglycemia and mammalian-like glucose tolerance profiles. Tilapia insulin differs structurally from human insulin which could preclude their use as islet donors for xenotransplantation. Therefore, we produced transgenic tilapia with islets expressing a humanized insulin gene. It is now known that fish genomes may possess an ancestral duplication and so tilapia may have a second insulin gene. Therefore, we cloned, sequenced, and characterized the tilapia insulin 2 transcript and found that its expression is negligible in islets, is not islet-specific, and would not likely need to be silenced in our transgenic fish.

Duplication and diversification of insulin genes in ray-finned fish

“…Both analyses generated similar phylogenies with independent duplications of the insulin gene on the spotted gar ( Lepisosteus oculatus ; infraorder Holostei) and teleost (infraorder Teleostei) fish lineages. While duplicated insa and insb genes were previously identified in teleost fish (Caruso & Sheridan, 2014; Hrytsenko et al, 2016; Irwin, 2004), here I find that these species have a third insulin paralog, which I named insc . The species relationships within each paralog of insulin genes, given its limited power at resolving species relationships, is in general agreement with the accepted phylogeny of teleost fish (Betancur-R et al, 2017; Near et al, 2012).…”

“…The selective forces acting on insb are weaker than those acting on insa (Table 1) suggesting that these two genes have different functions. Previous work indicates that insb is not appreciably expressed in the pancreas, and instead is more predominantly expressed in early development (Hrytsenko et al, 2016; Irwin, 2004; Papasani et al, 2006). The analysis of selective constraints and these expression results are consistent with speculation that insb is not primarily involved in the regulation of blood glucose level, but instead has a role in development (Hrytsenko et al, 2016; Papasani et al, 2006).…”

“…A subsequence study of the expression of the two insulin genes in zebrafish suggested that ins2 potentially has a function as a growth and neurotrophic factor during development (Papasani et al, 2006). More recently, studies of the tilapia ( O. niloticus ) ins2 gene showed that it had negligible expression in the pancreas, thus likely is not a major contributor to the regulation of glucose metabolism and would not need to be silenced to allow the xenotransplantation of tilapia islets as a treatment for diabetes in humans (Hrytsenko et al, 2016).…”

Data for evolutive analysis of insulin related peptides in bilaterian species

“…The dataset provides a list of hyperlinks to insulin-related peptides NCBI ID originating from various metazoan species (referenced as [1] , [2] , [3] , [4] , [5] , [6] , [7] , [8] , [9] , [10] , [11] , [12] , [13] , [14] , [15] , [16] , [17] , [18] , [19] , [20] , [21] , [22] , [23] , [24] , [25] , [26] , [27] , [28] , [29] , [30] , [31] , [32] , [33] , [34] , [35] , [36] , [37] , [38] , [39] , [40] , [41] , [42] , [43] , [44] , [45] , [46] , [47] , [48] , [49] ). For each sequence, the key motif of the A chain associated to the number and position of disulphide bonds was specified.…”