Abundant secretory lipocalins displaying male and lactation-specific expression in adult hamster submandibular gland, cDNA cloning and sex hormone-regulated repression

We have previously identified massively expressed 24- and 20.5-kDa male-spe cific proteins in submandibular salivary glands (SMG) of adult hamsters. He re we report the cloning Of the cDNA encoding the 24-kDa protein which we h ave now found to be a heterogenously N-glycosylated form of the 20.5-kDa pr otein. The deduced amino acid sequence indicated that the protein is a memb er Of the lipocalin family, the two most related lipocalins being rat odora nt-binding protein of nasal mucosa and aphrodisin. a pheromonal protein pre sent in vaginal discharge and saliva of female hamsters. Northern blot anal ysis showed that cognate mRNA is expressed in hamster SMG and lacrimal glan d (LG) displaying marked sex-hormonal repression. The sex-hormonal repressi on patterns showed similarities and dissimilarities between SMG and LG but they were, respectively, similar to the sex-hormonal repression pattern not ed for the SMG 24/20.5-kDa male-specific proteins and for an abundant femal e-specific 20-kDa LG secretory protein. These SMG and LG proteins were foun d to be immunologically similar and secretion of the SMG proteins in saliva and their excretion in urine was detected. The male-specific and abundant expression of the SMG proteins were seen at and after sexual maturity but w as not dependent on androgens. Surprisingly, a temporary male-like expressi on of these SMG proteins was seen in lactating females which was obliterate d by oestrogen administration. Our results show that despite differences in their repression by: sex;hormones, the gene for SMG 24/20.5-kDa proteins i s similar or identical to that of LG 20-kDa protein and their marked repres sion by both androgens and oestrogens might be at the transcriptional level . Moreover, they might be excellent models with which to study sex hormone repression of gene expression at the molecular level. The results of homolo gy search and the male- and lactation-specific pressure of the SMG proteins in adult saliva and urine suggests a possibility of their involvement in o lfaction-mediated chemical communication between hamsters.