Developmental and growth-related regulation of expression of serine dehydratase mRNA in rat liver

In rat liver, serine dehydratase mRNA is undetectable in the late prenatal period, but its level increases rapidly after birth to a transient peak, and then after decrease gradually increases again to a maximum 2 weeks after birth that is slightly higher than that of adult liver. To determine whether mature quiescent hepatocytes proliferate without loss of differentiated functions, we measured the serine dehydratase mRNA contents in regenerating liver and primary cultured hepatocytes from adult rats. Partial hepatectomy resulted in a dramatic decrease in the mRNA content within 24 h and then its recovery within a week. In subconfluent cultures of adult rat hepatocytes that did not grow even in the presence of mitogens, serine dehydratase mRNA was maintained at a high level. However, when the hepatocytes were cultured at low cell density without added mitogens, their serine dehydratase mRNA content decreases to a quarter of that of subconfluent cultures. The possibility that the expression of serine dehydratase mRNA is regulated in G0/G1 transition before entry into the S phase and the relationship of the mRNA with growth are discussed.