Thymosin beta 10 levels in developing human brain and its regulation by retinoic acid in the HTB-10 neuroblastoma.

Human fetal brain expresses high levels of a polypeptide identified by protein biochemistry and molecular cloning as thymosin beta 10. Within the first 18 months after birth, the thymosin beta 10 content of human brain falls to undetectable levels. In order to establish the molecular basis of this process we screened a number of human tumor cell lines derived from the nervous system for the presence of thymosin beta 10. All of the cell line expressed authentic thymosin beta 10. However, in the HTB-10 neuroblastoma, retinoic acid caused a reduction in the level of thymosin beta 10. This effect of the retinoid was conditional upon its continual presence in the tissue culture medium and was not evident in the other cell lines examined. These results suggest that the thymosin beta 10 gene may be a target for retinoids in the developing nervous system.