The development of rat α2‐macroglobulin

Abstract

During inflammation and tissue injury, there is an increase in the plasma concentration of several proteins, the acute‐phase proteins. The levels of some acute‐phase proteins have been reported to increase in pregnant and tumour‐bearing animals.Rat α2‐macroglobulin is classified as an acute‐phase protein. In this study we report the expression of α2‐macroglobulin in various tissues during development of the rat embryo by analysis of mRNA. The tissues studied are liver, viceral yolk sac, placental labyrinth, decidua and trophoblast. In addition, the sites of α2‐macroglobulin expression are localized by in situ hybridization of cDNA for α2‐macroglobulin to mid‐sagittal cryosections of rat embryos.The level of mRNA coding for α2‐macroglobulin is determined in the liver of rats aged between 12 days gestation and 2 days postnatal. α2‐Macroglobulin mRNA is first observed in fetal liver from 12 days of gestation and increases after day 17, reaching a maximum on day 20. At this time the level is greater than that found in the liver of an adult rat suffering from acute inflammation. α2‐Macroglobulin mRNA is detectable in the yolk sac, placental labyrinth, trophoblast tissue and decidua. In the decidua the α2‐macroglobulin message is first detected at 8 days of gestation, with high levels observed from 10 to 21 days of gestation. These observations are supported by in situ hybridization studies. Experiments using cultured hepatocytes show that cells derived from rats at 15 days and 19 days of gestation are capable of synthesizing and secreting α2‐macroglobulin. Both synthesis and secretion can be induced by the addition of dexamethasone to the culture medium.