Molecular Biology and Evolution, Vol 1, 335-344, Copyright © 1984 by Society for Molecular Biology and Evolution
LC Lopez, WH Li, ML Frazier, CC Luo and GF Saunders
Statistical analyses of DNA sequences of the preproglucagon genes from
bovine, human, hamster, and anglerfish suggest that a gene duplication
creating two anglerfish genes (AF I and II) occurred about 160 Myr ago,
long after the separation of fish and mammals. The analyses further suggest
that the internal duplication producing the glucagon and glucagon-like
peptide II (GLP-II) regions occurred about 1.2 billion years ago, which
would indicate that the GLP-II region was present in the ancestral
anglerfish sequence but was silenced or deleted before the gene duplication
separating AF I and II. The glucagon-like peptide I (GLP-I) was derived
from a duplication of the ancestral glucagon region about 800 Myr ago. The
rate of synonymous substitution in these genes is approximately 4.3 x
10(-9) substitutions per year per synonymous site. The rate of
nonsynonymous substitution in the signal peptide region is about 1.1 x
10(-9) substitutions per year per nonsynonymous site, a high rate
comparable to that in the C-peptide region of preproinsulin. The rate of
nonsynonymous substitution in the glicentin-related pancreatic polypeptide
(GRPP) region is 0.63 x 10(-9) for the comparisons between mammalian
species and 1.8 x 10(-9) for the comparisons between fish and mammals; the
moderate rate in mammals suggests a physiological role for GRPP. The
glucagon region is extremely conservative; no nonsynonymous substitution is
observed in the mammalian genes, and a nonsynonymous rate of 0.18 x 10(-9)
was obtained from the comparisons between fish and mammals. In the GLP-I
region, the rate of nonsynonymous substitution was estimated to be 0.08 x
10(-9) for the comparisons between mammalian species and 0.30 x 10(- 9) for
the comparisons between fish and mammals. In the GLP-II region, the rate
was estimated to be 0.25 x 10(-9) for the comparisons between mammalian
species. Thus, GLP-I and II are also very conservative, which suggests an
important physiological role for these peptides.
ORIGINAL ARTICLE
Evolution of glucagon genes
Department of Biochemistry and Molecular Biology, University of Texas System Cancer Center, M.D. Anderson Hospital and Tumor Institute, Houston 77030.
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