Detection of α-foetoprotein in mouse liver differentiated hepatocytes before their progression through S phase

Abstract

α-FOETOPROTEIN (AFP) is a serum protein present in large amounts during embryonic life and preserved in only nanogram quantities in adult mammals¹. Increased levels of AFP are seen in adults in association with two forms of tumours—teratocarcinomas and hepatocarcinomas—and also during liver regeneration². In early development AFP is synthesised in the yolk sac and in the liver^2,3 where it has been demonstrated by immunofluorescence in the majority of the hepatocytes⁴. Detailed aspects of AFP synthesis by hepatocytes, however, remain to be established. It has been suggested that it is synthesised by a definite population of hepatocytes⁵, by one of the stages in their differentiation^6,7, or by liver cell precursors⁸. Sufficient data to decide between these alternatives are not presently available. We describe here the immunohistochemical localisation of AFP in regenerating mouse livers, in which DNA-synthesising cells have been identified by thymidine incorporation. AFP was found in a minority of adult differentiated hepatocytes, many of which had not progressed through S phase. Thus DNA synthesis is not a prerequisite for the induction of AFP synthesis in the adult liver.