mRNA expression of secretory proteins in salivary glands

Objective: It has been reported that the same kinds of secretory proteins are detected in submandibular, parotid and sublingual glands, which have different cell composition, gland size and innervation. The purpose of this study is to know how these salivary glands contribute to the production of saliva. To investigate this, I studied the mRNA expression levels of secretory proteins in these glands in order to characterize the synthetic ability of these proteins.

Methods: Salivary glands from SD rats were removed and immediately soaked in RNAlater (Ambion) at 5°C. Total RNA was extracted using RNeasy Protect kit (Qiagen). Purified mRNA was obtained from total RNA using Absolutely mRNA Purification kit (Stratagene). Synthesis of first strand DNA was performed with oligo(dt)primer or random hexamer primers using the Transcriptor First Strand cDNA Synthesis kit (Roche Diagnostics). GAPDH amplification was used as a control. PCR was performed with KOD DNA polymerase (Toyobo). Semiquantitative analysis was performed using Image Gauge software (Fuji Film). Quantitative real-time PCR was performed using Light Cycler (Roche Diagnostics) and measured mRNA expression levels of secretory proteins in each salivary gland.

Results: Amylase, parotid secreted protein, cystatin S and proline-rich proteoglycans were expressed in parotid, submandibular and sublingual glands, respectively. Amylase and parotid secreted protein were expressed more strongly in the parotid gland than in the others. Cystatin S was expressed more strongly in the submandibular gland than in the others. Proline-rich proteoglycans were expressed at nearly the same level in all glands.

Conclusion: Almost all the secretory proteins examined were expressed in submandibular, parotid and sublingual glands, but the expression levels were different between these glands.