HUMAN CHORIONIC GONADOTROPIN-BETA GENE-EXPRESSION IN FIRST-TRIMESTER PLACENTA

The hCG beta gene family contains six genes linked in tandem on chromo some 19 and labeled beta genes 7, 8, 5, 1, 2, and 3. Previous studies on a small number of placentas have indicated that beta gene 5 was the most highly expressed gene during the first trimester of pregnancy, f ollowed by genes 3 and 8. beta genes 7, 1, and 2 were expressed at ver y low levels. The purpose of this study was to determine 1) whether th is pattern of expression was typical during normal pregnancy by sampli ng a large number of first trimester placentas, and 2) whether there w as a correlation between gestational age and the pattern of hCG beta g ene expression. Total RNA from 27 first trimester placentas varying in age from 6-16 weeks was reverse transcribed into complementary DNA. T he complementary DNA was amplified by PCR, and the amount of DNA repre sentative of each hCG beta gene was quantified by Genescan analysis. I n 14 of the 27 placentas, hCG beta gene 5 accounted for 50% or more of the total beta messenger RNA expressed. beta gene 3 was expressed at levels ranging from 1-42% of the total, and beta gene 8 expression ran ged from 12-32% of the total. Gene 7 expression was less than 3% of th e total beta expression in all 27 placentas. Although there appeared t o be a trend toward lower expression of beta gene 3 in placentas beyon d 10 weeks gestational age, there was no correlation of the pattern of beta expression with placental age. beta gene expression was also exa mined in two blighted ova, a spontaneous abortion sample, and a hydati diform mole as well as in cultured JAR choriocarcinoma cells. With the exception of JAR cells, these abnormal tissues had lour levels of gen e 3 expression, but these levels were within the range of the patterns observed in normal placentas. These data suggest that it is the total amount of hCG beta gene expression rather than the expression of indi vidual beta genes that is important for the maintenance of normal preg nancy.