Studies of an Knockout Corroborate a Role for Salivary ABP in Mouse Communication.

The house mouse () gene family is comprised of 64 paralogs, 30 and 34 , encoding the alpha (ABPA) and beta-gamma (ABPBG) protein subunits that are disulfide-bridged to form dimers in secretions. Only 14 genes are expressed in distinct patterns in the lacrimal (11) and submandibular glands (3). We created a knockout mouse line lacking two of the three genes expressed in submandibular glands, and , by replacing them with the resistance gene. The knockout genotype (-/-) showed no or transcripts in submandibular gland complementary DNA (cDNA) libraries and there was a concomitant lack of protein expression of ABPA27 and ABPBG27 in the -/- genotype saliva, shown by elimination of these two proteins from the saliva proteome and the loss of cross-reactive material in the acinar cells of the submandibular glands. We also observed a decrease in BG26 protein in the -/- animals, suggesting monomer instability. Overall, we observed no major phenotypic changes in the -/- genotype, compared with their +/+ and +/- siblings raised in a laboratory setting, including normal growth curves, tissue histology, fecundity, and longevity. The only difference is that male and female C57BL/6 mice preferred saliva of the opposite sex containing ABP statistically significantly more than saliva of the opposite sex without ABP in a Y-maze test. These results show for the first time that mice can sense the presence of ABP between saliva targets with and without ABPs, and that they spend more time investigating the target containing ABP.