The expression of mRNAs for hepatocyte growth factor/scatter factor, its receptor c-met, and one of its activators tissue-type plasminogen activator show a systematic relationship in the developing and adult cerebral cortex and hippocampus

The temporal and spatial expression in brain of the mRNAs for the pleiotropic cytokine hepatocyte growth factor/scatter factor (HGF/SF) and its receptor c-met were compared to those of a known HGF/SF activator, tissue-type plasminogen activator (tPA). In addition to the previously described expression in the developing and adult olfactory system [D.P. Thewke, N.W. Seeds, Expression of hepatocyte growth factor/scatter factor, its receptor, c-met, and tissue-type plasminogen activator during development of the murine olfactory system, J. Neurosci. 16 (1996) 6933-6944] two other regions of the mouse brain were found where the expression of tPA mRNA appeared to co-localized with HGF/SF and/or c-met mRNA. In the developing hippocampus, tPA mRNA was expressed coincident with HGF/SF and c-met mRNAs in the CA1 field. tPA mRNA was expressed in all areas of the adult hippocampus, while HGF/SF expression was restricted to the CA2 and CA3 fields, and c-met mRNA was seen primarily in the CA1 field. In the developing cerebral cortex, the expression of tPA mRNA was observed in the subplate and inner cortical plate between two layers of c-met expression, whereas HGF/SF mRNA was localized to the proliferative zone lining the lateral ventricle. Layer specific expression of both HGF/SF and c-met mRNA were observed in the adult cortex, where HGF/SF was expressed in layers IV and V and c-met in layers II-III, IV and V. The expression of tPA mRNA in the adult cortex was low and not layer specific, although homogenates of adult cortex did have detectable levels of tPA activity when subjected to zymography. Immunohistochemical analysis using HGF/SF and c-met antibodies on adult brain sections showed a distribution similar to the in situ hybridization results. C-met antibodies appeared to stain large neurons in the cortex and hippocampus. These results are consistent with the hypothesis that HGF/SF plays a role in the development and maintenance of both the cerebral cortex and hippocampus, and that tPA may act as a regulator of HGF/SF activity in these structures.