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 sever al hormones including thyroid hormone. This study was designed to clon e the gene whose expression is changed in association with perinatal h ypothyroidism in the rat cerebellum. Rats were sacrificed at 15 day-ol d postnatal age (P15) and their cerebella were removed. Poly (A)(+) RN A was extracted to construct a cDNA library using lambda gt 10 cloning vector. Differential plaque screening was then performed using P-32-l abeled antisense cDNA synthesized from poly (A)(+) RNA of the methimaz ole-treated (hypothyroid) P15 rat cerebellum (hypothyroid probe), and of the euthyroid P15 rat cerebellum (euthyroid probe). The clones, whi ch hybridized strongly to the euthyroid probe and weakly or not at all to the hypothyroid probe, were isolated. Sequence analysis of these c lones revealed that all isolated clones encode cytochrome c oxidase su bunit I (COX I), which is located in the mitochondrial DNA. The decrea se in COX I gene expression was not seen in the animals, which receive d methimazole treatment and daily replacement of thyroid hormone. In s itu hybridization detection showed not only overall decrease in COX I gene expression but also change in distribution of hybridization signa l in the cerebellar cortex of hypothyroid rat. Such change was not obs erved in the T-4-replaced animals. Based on the evidence that thyroid hormone greatly influences brain development, the results of the prese nt study indicate that the terminal enzyme of mitochondrial respirator y chain, COX I is one of the important target molecules regulated by t hyroid hormone in the newborn rat cerebellum.