Coexpression of liver-specific and growth-induced genes in perinatal and regenerating liver: Attainment and maintenance of the differentiated state during rapid proliferation

Abstract

The liver shows maximal cellular growth during fetal development and after partial hepatectomy. Exploring overlaps in gene expression patterns in these two types of hepatic growth may provide insight into common regulatory pathways. The expression of a large number of growth-induced and liver-specific genes induced in liver regeneration has been examined in the perinatal liver from several days prenatal to 4 weeks postnatal when the major growth phase of the liver ceases. As in liver regeneration, many growth-induced genes, such as PRL-1 and β-actin, are expressed at a high level throughout the temporal course of liver development and correlate with the proliferative state. The level of fetal liver expression of these genes is similar to peak expression found in the regenerating liver, suggesting that common pathways of transcriptional regulation exist in the two types of proliferation. A subset of liver-restricted immediate-early genes including, IGFBP-1, CL-6, and glucose-6-phosphatase (G6Pase) are induced in regenerating liver and may be important in maintaining hepatic metabolism during regeneration. In developing liver, these genes are expressed primarily in the perinatal period but, unlike the regenerating liver, are not coinduced. For instance, at birth, G6Pase is induced, whereas CL-6 is downregulated. In situ analyses confirm that a proliferation associated gene PRL-1 is expressed in multiple cell types throughout the developing liver, whereas the expression of liver-specific genes is confined to hepatocytes. Taken together, these findings imply that significant similarities and differences in transcriptional regulation and hormonal milieu exist in liver during regeneration and development. The increased expression of genes responsible for glucose homeostasis in proliferative states of the liver suggests that maintenance of differentiated function is a component of the hepatic growth response.