Isolation, sequencing and phylogenetic analysis of the two major functional domains of the ecdysteroid receptor gene (EcR) of a field crab inhabiting Indian peninsula: A first-time report

Abstract

The major functional domains (DNA binding domain, DBD and ligand-binding domain, LBD) of the ecdysteroid receptor gene (EcR), of the field crab (Parathelphusa hydrodromous) inhabiting the Indian peninsula are being elucidated in this paper. Oligo (dT) primed cDNA synthesis, PCR amplification and multiple sequence alignment (MSA) revealed that PhEcRDBD comprises 189 bp, showing 100% identity in amino acid sequence with those of all the six brachyuran crabs studied to date. PhEcRLBD (654 bp) has shown ~90 - 99% identity with Gecarcinucid/Parathelphusid field crabs; with other brachyurans and non-brachyurans, the identity declined perceptibly (~73 - 90%). Compared to PhEcRDBD, PhEcRLBD is less conserved, apparently due to its multiple functions such as homo/hetero dimerization and transcriptional activation/repression, in addition to ligand binding. MSA could locate non-synonymous substitutions, signifying differences in amino acid content existing among various taxa; this difference, however, does not seem to affect the efficacy of the ligand binding, evidenced by in silico docking studies. Interestingly, in addition to providing us with basic information on ecdysteroid receptors, the present MSA and phylogenetic analysis implicate the existence of parallelism between LBD sequence diversity and the habitat of the animal in question, in the order of – Gecarcinucid/Parathelphusid (field) crabs, non-Gecarcinucid/Parathelphusid (estuarine/marine crabs), non-brachyurans and non-crustacean arthropods, respectively.