A study of molecules involved in the regulation of the growth of haematopoietic cells and heart muscle cells in culture

Abstract

The description of the molecular events responsible for the control of cell division and differentiation is, currently, one of the major goals of molecular and cellular biologists. Cell and tissue culture techniques have proved to be promising laboratory tools for the study of the regulators of cellular growth and differentiation. Most cells in culture require specific polypeptide growth factors which are supplied by the addition of a complex biological fluid such as serum or, in some instances, by the cells themselves. These growth factors usually act on their target cell via a membrane receptor to which they bind. The events which occur after the growth factor binds to the membrane receptor have not been fully described, but the phosphorylation of tyrosine residues in certain proteins has been observed. A study was made of the polypeptide growth factors responsible for the growth and differentiation of haematopoietic cells in vitro. These growth factors, called colony - stimulating factors (C.S.F.'s) were prepared from human placental conditioned medium, giant cell tumour conditioned medium and pokeweed mitogen stimulated spleen conditioned medium. A C.S.F. from human placental conditioned medium was radioiodinated and the binding of the labelled growth factor to an anti-C.S.F. antiserum was studied. The binding studies indicated that a purer C.S.F. preparation and/or a more specific antiserum was necessary in order to establish a radioimmunoassay for C.S.F. The C.S.F.'s from giant cell tumour conditioned medium were purified by ultrafiltration, hydrophobic - interaction chromatography, gel filtration and thiolpropyl - sepharose 6B chromatography. Two peaks of biological activity were observed on gel filtration. One of these peaks gave an apparent MW of 63,000 and the other peak gave an apparent MW of 30,200. The C.S.F. from pokeweed mitogen stimulated spleen conditioned medium was labelled with peroxidase and the binding of the labelled-C.S.F. to bone marrow cell membranes studied. The labelled-C.S.F. bound to the membranes and the binding exhibited a linear relationship with membrane protein content. Also a defined growth medium for chick embryonic heart cells was developed. These cells were observed to differentiate from primitive foetal cells into mature "adult-type" cells. The cells grew as a monolayer, had spontaneous activity and were seen to beat.