Opossum carboxylesterases: sequences, phylogeny and evidence for CES gene duplication events predating the marsupial-eutherian common ancestor

Abstract

BackgroundCarboxylesterases (CES) perform diverse metabolic roles in mammalian organisms in the detoxification of a broad range of drugs and xenobiotics and may also serve in specific roles in lipid, cholesterol, pheromone and lung surfactant metabolism. Five CES families have been reported in mammals with human CES1 and CES2 the most extensively studied. Here we describe the genetics, expression and phylogeny of CES isozymes in the opossum and report on the sequences and locations of CES1, CES2 and CES6 'like' genes within two gene clusters on chromosome one. We also discuss the likely sequence of gene duplication events generating multiple CES genes during vertebrate evolution.ResultsWe report a cDNA sequence for an opossum CES and present evidence for CES1 and CES2 like genes expressed in opossum liver and intestine and for distinct gene locations of five opossum CES genes,CES1, CES2.1, CES2.2, CES2.3 and CES6, on chromosome 1. Phylogenetic and sequence alignment studies compared the predicted amino acid sequences for opossum CES with those for human, mouse, chicken, frog, salmon and Drosophila CES gene products. Phylogenetic analyses produced congruent phylogenetic trees depicting a rapid early diversification into at least five distinct CES gene family clusters: CES2, CES1, CES7, CES3, and CES6. Molecular divergence estimates based on a Bayesian relaxed clock approach revealed an origin for the five mammalian CES gene families between 328–378 MYA.ConclusionThe deduced amino acid sequence for an opossum cDNA was consistent with its identity as a mammalian CES2 gene product (designated CES2.1). Distinct gene locations for opossum CES1 (1: 446,222,550–446,274,850), three CES2 genes (1: 677,773,395–677,927,030) and a CES6 gene (1: 677,585,520–677,730,419) were observed on chromosome 1. Opossum CES1 and multiple CES2 genes were expressed in liver and intestine. Amino acid sequences for opossum CES1 and three CES2 gene products revealed conserved residues previously reported for human CES1 involved in catalysis, ligand binding, tertiary structure and organelle localization. Phylogenetic studies indicated the gene duplication events which generated ancestral mammalian CES genes predated the common ancestor for marsupial and eutherian mammals, and appear to coincide with the early diversification of tetrapods.

Genomic analysis of the carboxylesterases: Identification and classification of novel forms

“…The genomes of the chicken, chimpanzee, cow, dog, horse, human, medaka, mouse, opossum, orangutan, rat, rhesus monkey, stickleback, tetraodon, and zebrafish were subsequently mined for CE-related sequences based upon the cloned sequences for the human (Williams et al, 2008), cynomolgus monkey (cloned in this study), and dog (cloned in this study), as well as other known sequences (Satoh and Hosokawa, 2006;Holmes et al, 2008a). The genomes of non-vertebrate species were also searched, but sequences with a high nucleotide similarity were not found.…”

“…Based upon previously published CE sequences (Satoh and Hosokawa, 2006;Holmes et al, 2008a) and the cDNA sequences obtained in this study, Ensembl 50 (Flicek et al, 2008) was used to search the chicken, chimpanzee, cow, dog, horse, human, medaka, mouse, opossum, orangutan, rat, rhesus monkey, stickleback, tetraodon, and zebrafish genomes. Potential CE genes had two criteria to meet while being screened -(1) must have greater than a 50% nucleotide sequence similarity and (2) the nucleotide sequence length for each exon was greater than 50%.…”

“…Through examination of opossum and primate CE sequences, a case has been made for the existence of multiple CEs prior to the appearance of mammals (Holmes et al, 2008a(Holmes et al, , 2009. By carefully examining the current genomic databases, the discovery of additional CE-related genes can be greatly accelerated and potential pseudogenes can be identified.…”

Genetic variation in carboxylesterase genes and susceptibility to isoniazid-induced hepatotoxicity

“…CES1 and CES2 are the most extensively studied 51 ; CES4 is less well characterized. We found very high sequence similarity between CES1 and CES4; CES4 is likely to be an inverted duplication of CES1 (Figure 1).…”

Identification and characterization of an epididymis-specific gene, <italic>Ces7</italic>

“…CE family is considered to be products of ancestral gene duplication events [21]. And the conservation and tissue specificity of CES7 expression in male reproductive tracts of various species suggest its potential functions for sperm fertility.…”