Quantification of intracellular calcitonin gene transcripts in human medullary thyroid carcinoma (MTC) by in situ hybridization.

The human calcitonin gene generates 2 distinct mature mRNAs by alternative RNA processing, encoding calcitonin (CT) in thyroid C-cells or a neuropeptide (CGRP) in the brain. We evaluated quantitatively by in situ hybridization the expression of the CT gene in tissue section of 5 MTCs (2 sporadic and 3 familial forms). The primary tumor of one MTC was compared to a brain metastasis. In situ hybridization was carried out with tritiated cDNA probes coding for CT and CGRP mRNA. After autoradiography the number of silver grains was counted in 400 cells by computerized analysis of digitized images and expressed as the labelling level (L.L. = grain area/cell area per day of autoradiographic exposure). This was used to calculate the relative abundance per cell of the specific messengers studied, which depends on the autoradiographic efficiency and the specific activity of the probe used. The CT mRNA content was 3.25-6.55 10(-10) micrograms equivalents in the 3 familial forms of MTC and 4.95-9.25 10(-10) micrograms equivalents for the 2 sporadic forms. The levels of CT mRNA in the brain metastasis and in the primary tumor were identical (4.10 10(-10) micrograms equivalents). CGRP mRNA expression was weaker in the sporadic and in the familial thyroid tumors (0.60-1.65 10(-10) micrograms equivalents). The content of mRNA CGRP in the brain metastasis (0.60 10(-10) micrograms equivalents) was lower than that in the primary tumor (1.05 10(-10) micrograms equivalents).(ABSTRACT TRUNCATED AT 250 WORDS)