Early expression of thyroid hormone deiodinases and receptors in human fetal cerebral cortex

Thyroid hormones are known to be important for optimal development of the human central nervous system. Classically, maternal thyroid hormones have not been thought to have a major role in defining central nervous system development. However, recent epidemiological evidence has indicated that subtle deficiencies in circulating maternal thyroid hormones in the first trimester of pregnancy are associated with adverse neurodevelopment. We have used real time PCR to quantitate the expression of mRNAs encoding the thyroid receptor isoforms (TR alpha1, alpha2, beta1 and beta2) and thyronine deiodinase subtypes (5'-DI, 5'-DII and 5-DIII) in human fetal cerebral cortex from the first and second trimesters of pregnancy. Deiodinase subtype activities have also been determined in these tissues and compared to 'normal' adult human cerebral cortex. Iodothyronine deiodinase mRNAs were expressed in human fetal cerebral cortex from 7 to 8 weeks of gestation. The expression of 5'-DI mRNA was variable in fetal life but increased relative to adult cortex (P