DISTRIBUTION OF TRANSFERRIN-BINDING PROTEIN IMMUNOREACTIVITY IN THE CHICKEN CENTRAL AND PERIPHERAL NERVOUS SYSTEMS

Transferrin binding protein (TfBP) is a glycoprotein originally purifi ed from chicken oviduct that exhibits transferrin binding activity. Re cent work has shown that TfBP is a post-translationally modified form of the heat shock protein (HSP108), the avian homologue of a glucose r egulated protein, GRP94. The function of this protein, however, has no t yet been clearly defined. Antiserum to TfBP was found to selectively stain oligodendrocytes of the avian brain. In this study, we further describe these oligodendrocytes and other cell types positive to anti- TfBP in the chick nervous system. In accordance with previous studies, the most prominent cell type that labels with antiserum to TfBP is th e oligodendrocyte. At the electron microscopic level, the immunoreacti ve product is confined to the perinuclear cytoplasm and fine processes of the oligodendrocytes, whereas myelin and axoplasm are devoid of st aining. The immunoreactive product is found both in the cytoplasmic ma trix and bound to the endoplasmic reticulum and plasma membrane, sugge sting that TfBP may have properties of both a soluble and an integral membrane protein. There is great variability in the number of TfBP-oli godendrocytes in different areas of the central nervous system (CNS); large numbers of cells are associated with the white matter regions an d are found in the myelinated tracts, whereas few cells are present in the gray matter regions. In the retina, TfBP is localized specificall y in the cells that are morphologically oligodendrocytic and is presen t in the optic nerve fiber layer and the ganglion cell layer. Obvious staining is also seen in the Bergmann glial cells of the cerebellum an d in the Schwann cells of the sciatic nerve. Furthermore, the choroid plexus cells similarly exhibit a strong reaction. The association of T fBP in these specific cell types responsible for myelination and seque stering iron and transferrin implies that TfBP may be involved in myel ination and iron metabolism of the chick nervous system, perhaps throu gh a role in transferrin concentration in these cells. A putative role of TfBP, as HSP108, is considered. (C) 1997 Wiley-Liss, Inc.