LOCALIZATION WITH A DIGOXIGENIN-LABELED CRNA PROBE OF BASIC FIBROBLAST GROWTH-FACTOR MESSENGER-RNA IN DYSTROPHIC (MDX) MOUSE MASSETER MUSCLE AND RAT HAIR-FOLLICLES

In situ hybridization histochemistry with the use of a digoxigenin-lab eled ribonucleotide probe for basic fibroblast growth factor (bFGF) mR NA demonstrated bFGF transcripts in the masseter muscle of dystrophic (mdx) mouse and in vibrissae and small hair follicle of the rat peri-o ral skin. A conspicuous hybridization signal was detected in the centr al part of the cytoplasm of the smallest myoblasts in the process of i nitial regeneration or differentiation. bFGF mRNA staining decreased i n intensity as the myoblasts increased in size due to the production o f myofilaments. Endomysial fibroblasts and extracellular matrix did no t exhibit any detectable bFGF mRNA expression. In transverse sections of the hair follicles and vibrissae, a bFGF mRNA positive reaction was noted in the central portion of individual follicles, which were endo wed with a non-hybridized core of variable diameter. The hybridization signal in longituidinal sections of hair follicles was localized main ly to keratinizing hair cortical cells; the matrix was scarcely labele d with the probe. The dermal papillae of hair follicles were devoid of bFGF mRNA staining. These findings suggest that early regenerating or differentiating myoblasts produce bFGF, rather than internalizing the growth factor originating in other tissues and that part of bFGF gene rated in the hair cortical cells is conveyed to the hair matrix and ex ternal root sheath which has been shown, by immunohistochemistry, to c ontain bFGF-like substances.