P23 TRANSPLANTATION ANTIGEN MESSENGER-RNA IS DIFFERENTIALLY EXPRESSEDIN HUMAN FETAL BRAIN

As gene expression governs development, we attempted to isolate differ entially expressed genes in fetal and adult human brain. RNA samples e xtracted from adult and 18-24-week-old fetal human brain were reverse transcribed, amplified using twenty combinations of 3'-anchored primer s and degenerate 5'-primers, and the resulting cDNA fragments separate d on denaturing polyacrylamide gels. Thereafter, 45 (H1-H45) different ially displayed cDNA bands were extracted from the gels, amplified by polymerase chain reaction, and used as probes to detect their mRNA by northern blotting. One of these fragments, H8, confirmed on northern b lotting to be highly expressed in fetal brain, was cloned and sequence d. This fragment was homologous to wild type p23 human transplantation antigen. This is phylogenetically a well conserved gene and appears t o play an important role in cell growth. Even a single point mutation in the mouse gene results in cell destruction secondary to a cytotoxic T-lymphocyte response. Therefore, our finding that normal human fetal , brain expresses high levels of wild type p23 transplantation antigen may have importance in maintaining cell growth during human brain dev elopment.