title: Monotreme lactation protein is highly expressed in monotreme milk and provides antimicrobial protection.
abstract: Monotremes (platypus and echidna) are the descendants of the oldest ancestor of all extant mammals distinguished from other mammals by mode of reproduction. Monotremes lay eggs following a short gestation period and after an even briefer incubation period, altricial hatchlings are nourished over a long lactation period with milk secreted by nipple-less mammary patches located on the female's abdomen. Milk is the sole source of nutrition and immune protection for the developing young until weaning. Using transcriptome and mass spectrometry analysis of milk cells and milk proteins, respectively, a novel Monotreme Lactation Protein (MLP) was identified as a major secreted protein in milk. We show that platypus and short-beaked echidna MLP genes show significant homology and are unique to monotremes. The MLP transcript was shown to be expressed in a variety of tissues; however, highest expression was observed in milk cells and was expressed constitutively from early to late lactation. Analysis of recombinant MLP showed that it is an N-linked glycosylated protein and biophysical studies predicted that MLP is an amphipathic, α-helical protein, a typical feature of antimicrobial proteins. Functional analysis revealed MLP antibacterial activity against both opportunistic pathogenic Staphylococcus aureus and commensal Enterococcus faecalis bacteria but showed no effect on Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis, and Salmonella enterica. Our data suggest that MLP is an evolutionarily ancient component of milk-mediated innate immunity absent in other mammals. We propose that MLP evolved specifically in the monotreme lineage supporting the evolution of lactation in these species to provide bacterial protection, at a time when mammals lacked nipples.
authors.affiliation: School of Medicine, Deakin University, Geelong, Victoria, Australia aenjapoo@deakin.edu.au.
authors.forename: Ashwantha Kumar
authors.initials: AK
authors.lastname: Enjapoori
authors.affiliation: School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales, Australia.
authors.forename: Tom R
authors.initials: TR
authors.lastname: Grant
authors.affiliation: School of Biological Sciences, University of Tasmania, Hobart, Tasmania, Australia.
authors.forename: Stewart C
authors.initials: SC
authors.lastname: Nicol
authors.affiliation: School of Medicine, Deakin University, Geelong, Victoria, Australia.
authors.forename: Christophe M
authors.initials: CM
authors.lastname: Lefèvre
authors.affiliation: School of Medicine, Deakin University, Geelong, Victoria, Australia Department of Anatomy and Developmental Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Nicholas
authors.affiliation: School of Medicine, Deakin University, Geelong, Victoria, Australia Institute for Frontier Materials, Deakin University, Geelong, Victoria, Australia.
authors.forename: Julie A
authors.initials: JA
authors.lastname: Sharp
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D013293:Enterococcus faecalis / Q000187:drug effects; D004926:Escherichia coli / Q000187:drug effects; D019143:Evolution, Molecular; D010802:Phylogeny; D010987:Platypus / Q000378:metabolism; D011550:Pseudomonas aeruginosa / Q000187:drug effects; D019779:Salmonella enterica / Q000187:drug effects; D013211:Staphylococcus aureus / Q000187:drug effects; D004442:Tachyglossidae / Q000378:metabolism
chemical_list: D000890:Anti-Infective Agents
keywords: antibacterial protein; echidna; lactation; mammals; monotreme; platypus