A Minisatellite in the Growth Hormone Gene of Esocidae is Derived from a Single Copy Element in the Salmonid Genome
The growth hormone gene has been used to infer phylogenetic relationships in fishes, and in closely related species the intronic sequence has shown particular value in discriminating among taxa. We examined the growth hormone gene in the esocid family by cloning the fourth intron of the growth hormone gene from all five esocid species. Our initial analysis identified a 33-nucleotide minisatellite in the fourth intron that is present in copy numbers ranging from seven to 16 among the various species. Database searches indicate that this minisatellite is present only as a single copy element in all of the salmonids, indicating a recent expansion in the esocid species since their divergence from a common ancestor. The minisatellite was not detected in any other growth hormone sequences available at the time of this writing. Furthermore, point mutations and deletions in the esocid minisatellites indicate a model for the evolution of this genetic element and corroborate existing molecular phylogenies for the five members of this genus.Abstract
Comparison of the growth hormone genes of Salmo salar, Esox masquinongy, and E. lucius.
(A) Exons 2 through 6 of the GH gene of S. salar and (B) Esox masquinongy showing relative sizes and indicating the location of the primers used in this study. (C) Comparison of the amino acid sequences of E. lucius (E.l.), E. masquinongy (E.m.), and S. salar (S.s.). Arrows in the first and last nine codons represent locations of the primers. Non-conservative substitution at amino acid 121 is marked with a box. Periods (.) represent consensus and dashes (-) represent gaps in the alignment.
Alignment of the repeated minisatellites with the homologous sequence from Salmo salar. Repeats from each species are identified by letter and number: S. salar (Sal); Esox masquinongy (m1–m13); E. lucius (l1–l12); E. reicherti (r1–r16); E. niger (n1–n7); E. americanus (a1–a7). Periods (.) represent consensus and dashes (-) represent gaps in the alignment.
Fifty-percent majority-rule consensus of equally parsimonious trees for the minisatellites. Percent consensus values are indicated on the branches. Repeats from each species are identified by letter and number: Esox masquinongy (m1–m13); E. lucius (l1–l12); E. reicherti (r1–r16); E. niger (n1–n7); E. americanus (a1–a7).
Contributor Notes
(KRB, DKP) Department of Biological and Environmental Sciences, Morehead State University, Morehead, Kentucky 40351; and (RLH) Department of Zoology, Southern Illinois University, Carbondale, Illinois 62901. E-mail: (DKP) d.peyton@moreheadstate.edu. Send reprint requests to DKP.