Developmental changes in microheterogeneity of foetal plasma glycoproteins of mice

Changes in microheterogeneity of foetal plasma glycoproteins during development of mouse embryos were investigated. Analysis of foetal plasma by polyacrylamide-gel electrophoresis indicated three major zones of proteins: (1) transferrins, (2) alpha-foetoproteins and (3) albumin. Three transferrins (Tr1, Tr2, Tr3) and five alpha-foetoproteins (Fp1, Fp2, Fp3, Fp4, Fp5) were resolved. Evidence for the presence of transferrins was the binding of (59)Fe to the three electrophoretic variants. By day 15.5 of gestation, there was a marked increase in the more-acidic components (Tr3, Fp4, Fp5) and a decrease in the less-acidic ones (Tr1, Tr2, Fp1, Fp2, Fp3). Treatment of foetal plasma with neuraminidase at this time of development converted the more acidic components into Tr1 and Tr2 and Fp1, Fp2 and Fp3. Furthermore, it was shown that early in development (day 12.5) only the less-acidic components of transferrin and alpha-foetoprotein were synthesized; at the later time in development (day 14.5) new synthesis of the acidic components of both groups occurred. That these more-acidic components of alpha-foetoprotein (Fp4, Fp5) were in fact electrophoretic variants of the less-acidic alpha-foetoproteins was shown by the immunoprecipitation of labelled Fp4 and Fp5 with anti-Fp1, anti-Fp2 and anti-Fp3. From these results it is postulated that the plasma glycoproteins that are synthesized later in development contain increased amounts of sialic acid and that the observed changes in microheterogeneity of these proteins represent regulation of glycoprotein biosynthesis at the level of carbohydrate attachment.