EFFECT OF PERINATAL HYPOTHYROIDISM ON EXPRESSION OF CYTOCHROME-C-OXIDASE SUBUNIT-I GENE, WHICH IS CLONED BY DIFFERENTIAL PLAQUE SCREENING FROM THE CEREBELLUM OF NEWBORN RAT

Early development of the central nervous system is influenced by several hormones including thyroid hormone. This study was designed to clone the gene whose expression is changed in association with perinatal hypothyroidism in the rat cerebellum. Rats were sacrificed at 15 day-old postnatal age (P15) and their cerebella were removed. Poly (A)(+) RNA was extracted to construct a cDNA library using lambda gt 10 cloning vector. Differential plaque screening was then performed using P-32-labeled antisense cDNA synthesized from poly (A)(+) RNA of the methimazole-treated (hypothyroid) P15 rat cerebellum (hypothyroid probe), and of the euthyroid P15 rat cerebellum (euthyroid probe). The clones, which hybridized strongly to the euthyroid probe and weakly or not at all to the hypothyroid probe, were isolated. Sequence analysis of these clones revealed that all isolated clones encode cytochrome c oxidase subunit I (COX I), which is located in the mitochondrial DNA. The decrease in COX I gene expression was not seen in the animals, which received methimazole treatment and daily replacement of thyroid hormone. In situ hybridization detection showed not only overall decrease in COX I gene expression but also change in distribution of hybridization signal in the cerebellar cortex of hypothyroid rat. Such change was not observed in the T-4-replaced animals. Based on the evidence that thyroid hormone greatly influences brain development, the results of the present study indicate that the terminal enzyme of mitochondrial respiratory chain, COX I is one of the important target molecules regulated by thyroid hormone in the newborn rat cerebellum.