Characterization of two whey protein genes in the Australian dasyurid marsupial, the stripe-faced dunnart (Sminthopsis macroura)

We report the first isolation and sequencing of genomic BAC clones containing the marsupial milk protein genes Whey Acidic Protein (WAP) and Early Lactation Protein (ELP). The stripe-faced dunnart WAP gene sequence contained five exons, the middle three of which code for the WAP motifs and four disulphide core domains which characterize WAP. The dunnart ELP gene sequence contained three exons encoding a protein with a Kunitz motif common to serine protease inhibitors. Fluorescence in situ hybridization located the WAP gene to chromosome 1p in the stripe-faced dunnart, and the ELP gene to 2q. Northern blot analysis of lactating mammary tissue of the closely related fat-tailed dunnart has shown asynchronous expression of these milk protein genes. ELP was expressed at only the earlier phase of lactation and WAP only at the later phase of lactation, in contrast to β-lactoglobulin (BLG) and α-lactalbumin (ALA) genes, which were expressed in both phases of lactation. This asynchronous expression during the lactation cycle in the fat-tailed dunnart is similar to other marsupials and it probably represents a pattern that is ancestral to Australian marsupials.