Metastasis-associated Mts1 (S100A4) protein in the developing and adult central nervous system

We have found recently that white matter astrocytes in the spinal cord cons titutively express immunoreactivity for Mts1 (S100A4) protein and that this expression is up-regulated ipsilaterally after sciatic nerve or dorsal roo t injury. Here, we have studied the expression pattern of Mts1 throughout t he rat central nervous system (CNS). We found Mts1 immunoreactivity in myel inated tracts such as the olfactory tract, optic nerve, corpus callosum, in ternal capsule, fimbria, and spinal cord funiculi but not in cerebellar whi te matter. Mts1-immunoreactive (IR) cells were consistently astrocytic (gli al fibrillary acidic protein positive). In addition to myelinated tracts, M ts1 immunoreactivity was also present in a few nonmyelinated or poorly myel inated areas, such as pituitary gland, olfactory bulb, and around the later al ventricle. Based on location, three Mts1-IR astrocyte groups were distin guished: 1) astrocytes at the surfaces of the CNS, i.e., adjacent to the ce rebrospinal fluid, organized perpendicularly to the bundles of axonal tract s; 2) astrocytes located in parallel to, and inserted between, axonal bundl es; and 3) clusters of astrocytes around the lateral ventricle and in the o lfactory bulb. We further analyzed the relationship between Mts1 immunoreac tivity and the development of CNS fiber tracts by combining staining for Mt s1 and myelin basic protein (MBP). Mts1 immunoreactivity appeared postnatal ly in recently myelinated areas. During the development of corpus callosum and the optic tract, Mts1 immunoreactivity was concentrated at the frontier of myelination. The developmental expression pattern suggests a role of Mt s1-IR astrocytes in the maturation of myelinated fiber tracts. The preferen tial localization of Mts1 to the subpial. region in the mature CNS suggests that Mts1 participates in astrocyte-mediated CNS-cerebrospinal fluid excha nge. J. Comp. Neurol. 424: 269-282, 2000. (C) 2000 Wiley-Liss, Inc.