Membrane transport during development in animals.

This brief and necessarily incomplete survey of available evidence on the development of transport systems in animal cells reveals a primitive state of knowledge full of interesting possibilities for future development. The assembly of membrane-bound transport systems during embryonic development provides unique opportunities for approaching questions relating to gene expression, the synthesis and insertion of membrane proteins into phospholipid layers, the composition and structure of transport systems and the conditions required for their functioning. It seems plausible to assume that the growth and differentiation of animal cells is regulated, in part at least, by the rate of transport of metabolites and ions across the cell membranes. Therefore the sequence of the expression of transport systems is likely to have a profound effect on subsequent stages of growth and differentiation. Feedback regulation of the synthesis of transport proteins by changes in the intracellular or extracellular concentrations of the transported metabolites or ions [52, 53, 85-87] may be a key element in the regulation of the rate of transport processes during development.