Active uptake and transport of protein by the intestinal epithelial cells in embryo of viviparous fish, Neoditrema ransonneti (Perciformes: Embiotocidae).

Neoditrema ransonneti is a matrotrophic viviparous fish. To clarify the site and process of protein uptake in the fetus of N. ransonneti, rabbit IgG and equine ferritin were administered into the ovarian cavity of pregnant females. Both proteins were absorbed by epithelial cells of hypertrophied intestine within 2h. Rabbit IgG appeared to be concentrated in large cytoplasmic vacuoles of which diameter sometimes reached more than 2 micro m. On the other hand, electron microscopy showed that ferritin was transported as middle-sized granules (smaller than 1 microm) and not accumulated in large vacuoles. The granules were transported through intra- and inter-cellular pathways and released into submucosal spaces. Furthermore, a number of fine granules of ferritin were seen in the lumen of intravillus capillaries. Western blotting showed that absorbed the rabbit IgG reached the circulating blood intact. These findings suggest that fetuses of N. ransonneti actively absorb maternally supplied proteins via enterocytes, and exploit them not only as nutrients but also as physiologically active molecules. Copyright 2004 Wiley-Liss, Inc.