Evolution of hypothalamus-pituitary growth axis among fish, amphibian, birds and mammals

Hypothalamus-pituitary growth axis (HP growth axis) regulates animal growth and development in pre-natal and post natal life governed by many factors. However, until recently, the evolutionary history of this axis among lineages is not understood. Aim of the present study was to understand the major events in evolution and evolutionary history and trend of HP growth axis. The diversity among Homo sapience, Mus musculus, Rattus norvegicus, Gallus gallus, Danio rerio and Xenopus laevis was determined for genes involved in HP growth axis in current study. Sequences of HP growth axis genes were retrieved from NCBI (http://www.ncbi.nlm.nih.gov/). Nucleotide diversity using Kimura?s two-parameter method; codon-based test of positive selection using the Nei-Gojobori; equality of evolutionary rate with Tajima's relative rate test and phylogenetic history using the RelTime method were estimated in MEGA6. Estimates of the coefficients of evolutionary differentiation based on nucleotides and amino acids substitution patterns of HP growth axis genes showed contrasting evolutionary patterns among the lineages. The results demonstrated that although these genes might have crucial functional roles in each of the species, however, their sequence divergence did not necessarily reflect similar molecular evolution among the species. Codon-based test of positive selection revealed that Human vs Mouse, Chicken vs Rat, Human vs Rat and Mouse vs Rat had similar and higher non synonymous substitutions (P > 0.05). Higher rate of non-synonymous substitutions at similar orthologs level among species indicated a similar positive selection pressure in these species. Results for relative rate test assessed with the chi-squared test showed difference on unique mutations among lineages at synonymous and non synonymous sites except Chicken vs Mouse, Human vs Mouse, Chicken vs Rat, Human vs Rat and Mouse vs Rat. This indicated that the mutagenic process that generates substitutional mutation is taking place at approximately the same rate at synonymous and non-synonymous sites these lineages. Moreover, despite of common ancestry, our results indicate a different divergent time among genes of these species. This is the first demonstration that variable rates of molecular evolution may be present within HP growth axis genes among different species. This difference could be of interest for comparative genomics analysis and physiological genes functions identification among tho comparative genomics, evolution rate, HP growth axis, positive selection se species whose HP growth axis is not explored.