Changes in rat alpha 1-fetoprotein and albumin mRNA levels during fetal and neonatal development.

Rat alpha 1-fetoprotein (AFP) and albumin mRNA levels have been examined in yolk sac and liver during late gestation and early neonatal life by cell-free translation and RNA-excess cDNA hybridization. AFP-specific sequences were found to comprise up to 25% of the total poly(A)-containing RNA in the yolk sac, and they were reduced about 10-fold in the fetal liver. Since comparable amounts of poly(A)-containing RNA were obtained from both tissues, these observations suggest that the yolk sac may be the major source of maternal and fetal plasma AFP in late gestation. The level of AFP mRNA sequences in fetal liver remained relatively constant during the last week of gestation and the first 2 weeks of neonatal life. In contrast, the concentration of albumin sequences increased steadily during this time, reaching about 85% of adult levels by 2 weeks of age. These results suggest that the expression of AFP and albumin genes may not be reciprocally regulated, but rather they may be regulated independently of each other during the perinatal period. Albumin-specific sequences were also detected in the poly(A)-containing RNA from yolk sac but at a level of more than 400-fold lower concentration than that of the fetal liver. It was especially noteworthy that the relative level of AFP sequences in the yolk sac decreased much earlier than that in the liver. Thus, AFP gene expression may be subject to different developmental controls in these two tissues. The continuation of AFP production in the liver following birth may indicate a continuing functional requirement for this protein in early neonatal life.