Expression of v-Ha-ras driven by the calcitonin/calcitonin gene-related peptide promoter: a novel transgenic murine model for medullary thyroid carcinoma

v-Ha-ras has been demonstrated previously to induce neuroendocrine differentiation of medullary thyroid carcinoma (MTC, malignant C cell tumor) cell lines. The potential role of ras mediated signaling in neuroendocrine cells in vivo has been investigated by expressing v-Ha-ras under control of the neural/neuroendocrine specific calcitonin/calcitonin gene-related peptide (CGRP) promoter. Five independent mouse lineages were derived following germ line insertion of the transgene. Four of the five lineages consistently express the transgene; neuroendocrine expression is found in three of the five lineages as both spliced and full length messages. Phenotypically, the mice expressing rascal have shortened lifespans primarily due to the high incidence of MTCs between 6 months to a year of age. C-cell hyperplasia is demonstrated in several mice in the absence of gross evidence of tumor formation. Histopathological and ultrastructural analyses demonstrate typical features of MTCs including prominent immunohistochemical staining for calcitonin and dense-core neurosecretory-type granules. In addition, four of 22 tumors co-express thyroglobulin (a non-neuroendocrine follicular epithelial cell marker) and calcitonin (a neuroendocrine marker) in a subset of the tumor cells. The rascal transgenic mouse provides a unique model for investigating the sequential pathogenesis of MTC and possibly also for elucidating the relationship between MTC and mixed medullary-follicular carcinomas.