Differential expression of Huntington's disease gene (IT15) mRNA in developing rat brain.

Huntington's disease (HD) is an autosomal dominant inheritance neurological disorder associated with CAG repeats expansions within a widely distributed gene that causes selective neuronal death. The gene is essential for normal development and has been suggested for its role in the development of basal ganglia. To understand its normal function during growth and development, we determined the expression patterns for the gene responsible for HD (IT15) mRNA by Northern blot analysis in the developing and adult rat brain. In adult rat brains, IT15 transcripts exist as two isoforms of 10 and 12.5 kb each, which display distinct expression patterns. IT15 mRNA expression is already highly expressed within 1 day of birth. Expression signals for IT15 were first detected at embryonic day 16 or 17 during prenatal development. IT15 transcript peaks leveled around day 20 postnatally and thereafter decreased to levels typically found in adults. In the adult rat brain, mRNA expression was highest in the cerebellum followed by the cortex, striatum, hippocampus and olfactory lobe. In the medulla and the spinal cord, IT15 was weakly expressed in comparison to the other regions studied. Thus, the distinct expression patterns provide a basis for its functional significance during development. These results also suggest that the degree of IT15 mRNA expression is related to the neuronal population in different brain regions.