Harderian gland hyperplasia in c-mos transgenic mice.

Transgenic mice carrying the mouse mos proto-oncogene linked to a retroviral LTR develop hyperplasia of the Harderian glands. Enlargement of the glands is evident as early as 18 weeks after birth, with glands reaching up to 10 times their normal weight. Approximately 65% of the cases of hyperplasia occur bilaterally, and the majority of mice affected are male (66%). Elevated levels of mos expression are found in all Harderian glands of mice from the affected transgenic line, but not in glands of normal mice or a non-affected transgenic line, indicating that hyperplasia is dependent on mos expression. Histological examination of the tissue reveals a general involvement of the entire gland epithelium in hyperplastic growth, with no evidence of focal or malignant tumours. These observations show that in addition to neu, myc, ras and ret transgenes, mos, a member of the protein-serine/threonine kinase family of oncogenes, can induce Harderian gland hyperplasia, thus revealing an unusual response by this organ to various classes of oncogenes. Analysis of fos, jun, myc and ets oncogene RNA in mos-induced hyperplastic Harderian glands shows that there are no consistent changes in the level of expression of these oncogenes, suggesting that mos acts via a mechanism other than by increasing the expression of these genes.