STUDIES ON THE METABOLISM OF CELLS IN VITRO : I. THE TOXICITY OFalpha-AMINO-ACIDS FOR EMBRYONIC CHICKEN CELLS

Fibroblasts: Origins, definitions, and functions in health and disease

Fibroblasts are diverse mesenchymal cells that participate in tissue homeostasis and disease by producing complex extracellular matrix and creating signaling niches through biophysical and biochemical cues. Transcriptionally and functionally heterogeneous across and within organs, fibroblasts encode regional positional information and maintain distinct cellular progeny. We summarize their development, lineages, functions, and contributions to fibrosis in four fibroblast-rich organs: skin, lung, skeletal muscle, and heart. We propose that fibroblasts are uniquely poised for tissue repair by easily reentering the cell cycle and exhibiting a reversible plasticity in phenotype and cell fate. These properties, when activated aberrantly, drive fibrotic disorders in humans.

PHYSIOLOGICAL ONTOGENY : A. CHICKEN EMBRYOS. IV. THE NEGATIVE ACCELERATION OF GROWTH WITH AGE AS DEMONSTRATED BY TISSUE CULTURES

1. Observations on tissue cultures of heart muscle from chicken embryos indicate that in general the growth rate of the individual cells decreases with age. The negative acceleration of growth is greatest at the beginning of life as in the intact embryo. 2. The latent period before growth commences increases with the age of the implanted tissue, but in a different fashion. The acceleration of the latent period is greatest near the end of the incubation period, thus demonstrating that the factors determining the initiation of growth and those determining the extent of growth are not similar.

THE CHEMICAL NATURE OF SUBSTANCES REQUIRED FOR CELL MULTIPLICATION

1. Fibroblasts and epithelial cells in pure culture obtain the nitrogen, which they build into protoplasm, from proteoses and possibly other primary derivatives of proteins. These proteoses have been prepared from embryo tissues, egg white, commercial fibrin, rabbit brain, Witte's peptone, etc. 2. The presence in embryo juice of a hormone that stimulates cell division is improbable. 3. Proteoses separated from peptic digests of fibrin by sodium sulfate determine a more abundant and prolonged multiplication of the fibroblasts than is produced by embryo juice. Peptones and the smaller split products appear to furnish some nutrient material, but do not cause the rapid proliferation characteristic of proteoses, and are sometimes toxic for tissue cells. 4. Possibly the effect of embryo juice on fibroblasts and epithelium is due to the splitting of the protein of the juice into proteoses by the cell enzymes, or by other enzymes activated by the presence of living cells.