Electron microscopic immunocytochemical localization of proline-rich proteins in normal mouse parotid salivary glands

Proline-rich-protein promoters direct LacZ expression to the granular convoluted tubular cells of the submandibular gland in adult transgenic mice

The ability of two mouse PRP gene promoters to direct the expression of the bacterial lacZ reporter gene was tested in transgenic mice. Transgenes A1-lacZ and C1-lacZ consisted of 8.2 kb A1 and 7.8 kb C1 PRP promoters respectively fused to the lacZ coding sequence. A1 and C1 are two A-type PRP genes isolated from the inbred SWR mice, which show the same gene structure and similar sequence to the closely related MP2 and M14 PRP genes previously cloned from outbred CD-1 mice. We here show that both A1-lacZ and C1-lacZ transgenes have very similar expression patterns: (1) they expressed the lacZ gene in all 14 established transgenic lines under normal (non-stimulated) conditions; (2) the expression was restricted to the granular convoluted tubular cells of the submandibular glands; (3) the expression was developmentally regulated beginning at sexual maturation and lasting to at least 1.5 years of age; and (4) expression in some lines was probably influenced by sex hormones, since higher expression was found in males than in females. A1-lacZ and C1-lacZ are the first transgenes derived from the PRP/GRP (glutamine/glutamic acid-rich protein) gene superfamily to be expressed in the granular convoluted tubular cells (with known endocrine functions), rather than in the acinar cells (with mainly exocrine functions) of the submandibular glands.