Exogenous transferrin is taken up and localized by the neurulation-stage mouse embryo in vitro.

We have screened neurulation-stage mouse embryos for regional differences in protein distribution, by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The screen has revealed an 83-kD protein (pI 6.8) that is present in embryo regions where neurulation is in progress but not in regions where neurulation is complete. The 83-kD protein is not synthesized in the neurulation-stage embryo or in the yolk sac, but is taken up from the culture serum in vitro and, probably, from the maternal serum in utero. The 83-kD protein has been identified as transferrin on the basis of its electrophoretic migration and recognition on Western blots by an antitransferrin antibody. Culture of embryos in serum containing 125I-transferrin, followed by autoradiography of embryo sections, shows that transferrin is taken up and localized in the gut beneath the closing neural folds at several levels of the body axis in 8.5- and 9.5-day embryos. In situ hybridization studies show that the transferrin receptor mRNA is expressed in all cells of the 9.5-day embryo, including the gut endoderm. These findings are consistent with a role for transferrin in development of the gut and perhaps, indirectly, in completion of neurulation during early mouse embryogenesis.