Postnatal expression of sialin in the mouse submandibular gland

Sialin has been identified as a sialic acid and aspartate/glutamate transporter. Both cytoplasmic localization and the plasma membrane labelling pattern suggested that sialin may possess multiple transport functions in different cell types. In mouse embryos, sialin expression was primarily detected in the central nervous system. However, sialin shows widespread and high-level expression in adult tissues. Despite its ubiquitous expression and important functions, the postnatal expression profile and subcellular localization of sialin in the salivary gland remains elusive. The aim of the present study was to investigate the expression and subcellular distribution of sialin during postnatal development in the mouse submandibular gland (SMG).

Six SMGs from both female and male C57BL/6 mice were collected at P10, P30 and P90, and the material from each littermate of either sex was pooled to extract total RNA and tissue protein. The remaining tissues were immediately fixed in 10% neutral buffered formalin for histological analysis. The mRNA and protein expression levels of sialin were examined by quantitative real-time RT-PCR and Western blot analysis. The subcellular distribution of sialin was analysed by immunohistochemistry and immunofluorescence.

The postnatal expression level of sialin in the mouse SMG was comparable with that in brain at each time point tested. The temporal expression of sialin in the SMG gradually increased during postnatal maturation. Immunohistochemical and immunofluorescence analysis demonstrated that sialin was predominantly expressed on the basal cytoplasmic membrane of acini and ducts, as well as in some myoepithelial cells in the SMG.

The high-level expression and subcellular distribution pattern of sialin in the SMG suggest that sialin may play an important role in the transport and secretion of saliva.