[The fibroblast, definition of its phenotype by its "programme" of biosynthesis of the extracellular matrix]

This presentation is an introduction to a symposium focusing on the fibroblast, a virtually ubiquitous cell which is cultured in many laboratories. The traditional definition of the fibroblast based solely on morphological criteria, which has satisfied most biologists for years, now needs reappraisal. The papers delivered at this symposium addressed this issue. Investigations ranged from the phylogenetic origin of fibroblasts in sponges, studied by R. Garrone, to the phenotypic modulations leading to the "myofibroblast" reported by G. Gabbiani, whose manuscript was unfortunately received too late for the conference. The present article describes how the fibroblast can be defined on the basis of its programme for producing extracellular matrix macromolecules. This programme includes a qualitative aspect, i.e., the selection of genes to be expressed: collagen types, variations in alternative splicing patterns of matrix proteins--and a quantitative aspect, i.e., the precise spatial and temporal regulation of production of "selected" macromolecules in order to meet the body's needs. This programme can be studied experimentally, and data are accumulating on the mechanisms involved and on its regulation through intrinsic factors (acting on the genome) and extrinsic and epigenetic factors (vitamins, hormones, nutrition...). Several French laboratories have supplied useful contributions to this research. The results of their investigations, which cover part of this field, are reproduced in this issue of this revue.