The mammary gland-specific marsupial ELP and eutherian CTI share a common ancestral gene

Abstract

BackgroundThe marsupial early lactation protein (ELP) gene is expressed in the mammary gland and the protein is secreted into milk during early lactation (Phase 2A). Mature ELP shares approximately 55.4% similarity with the colostrum-specific bovine colostrum trypsin inhibitor (CTI) protein. Although ELP and CTI both have a single bovine pancreatic trypsin inhibitor (BPTI)-Kunitz domain and are secreted only during the early lactation phases, their evolutionary history is yet to be investigated.ResultsTammar ELP was isolated from a genomic library and the fat-tailed dunnart and Southern koala ELP genes cloned from genomic DNA. The tammar ELP gene was expressed only in the mammary gland during late pregnancy (Phase 1) and early lactation (Phase 2A). The opossum and fat-tailed dunnart ELP and cow CTI transcripts were cloned from RNA isolated from the mammary gland and dog CTI from cells in colostrum. The putative mature ELP and CTI peptides shared 44.6%-62.2% similarity. In silico analyses identified the ELP and CTI genes in the other species examined and provided compelling evidence that they evolved from a common ancestral gene. In addition, whilst the eutherian CTI gene was conserved in the Laurasiatherian orders Carnivora and Cetartiodactyla, it had become a pseudogene in others. These data suggest that bovine CTI may be the ancestral gene of the Artiodactyla-specific, rapidly evolving chromosome 13 pancreatic trypsin inhibitor (PTI), spleen trypsin inhibitor (STI) and the five placenta-specific trophoblast Kunitz domain protein (TKDP1-5) genes.ConclusionsMarsupial ELP and eutherian CTI evolved from an ancestral therian mammal gene before the divergence of marsupials and eutherians between 130 and 160 million years ago. The retention of the ELP gene in marsupials suggests that this early lactation-specific milk protein may have an important role in the immunologically naïve young of these species.

A Novel Highly Divergent Protein Family Identified from a Viviparous Insect by RNA-seq Analysis: A Potential Target for Tsetse Fly-Specific Abortifacients

“…Previous examination of mammalian milk proteins revealed that discrete, specific sections of each gene are subject to neutral, negative or positive selection [32] . Using a similar MEGA-based analysis to specifically investigate MGP2–10 from G. morsitans , the secretory peptide and conserved region 1 appear to be largely under negative selection ( Fig.…”

“…Under the FEL method, posterior probabilities cutoffs were set at 95, which is equivalent to a p-value of 0.05 for the site-specific detection of codons under positive or negative selection. Analysis of specific regions of the MGP2–10 coding regions was conducted using MEGA5 according to previous milk protein studies [32] and individual regions were based upon protein coding regions with high or low levels of amino acid homology.…”

Desmoglein-2 during pregnancy and its role in the evolution of viviparity in a marsupial (Sminthopsis crassicaudata; Dasyuridae)

“…The Dasyuridae (carnivorous marsupials) have a minimally invasive (endotheliochorial) placenta, termed the marsupial yolk sac placenta, which forms once the shell coat ruptures in the last third of pregnancy (Renfree et al, ). Marsupials have a low maternal physiological investment during gestation when compared to that of many eutherian mammals, and marsupials have an extended lactation period (Pharo et al, ). Characterisation of desmosome expression in the uterine epithelium of marsupials during pregnancy will thus allow us to assess the generality of plasma membrane changes during pregnancy across mammalian species with similar placenta types and invasiveness.…”

The identification of immune genes in the milk transcriptome of the Tasmanian devil (Sarcophilus harrisii)

“…It is possible that devils and wallabies are recruiting different proteins to fulfil the amino acid requirements of their PY, or that the differences in expression are due to additional functions of these proteins, for example several of these proteins are believed to play an immune role. ELP is likely to be a protease inhibitor, acting to prevent Ig degradation in the gut of the young ( Pharo et al, 2012 ) while β -lactoglobulin can be digested into anti-bacterial peptides in the gut ( Jenness, 1986 ; Pellegrini et al, 2001 ).…”