The investigations described here were begun at
the suggestion of Professor G. F. Marrian and. Professor J. R. Learmonth to examine the relationship between ribonucleic acids (and their derivatives) and
the processes of tissue growth (including wound healing).
Examination of the literature suggested that
ribonucleic acid derivatives might be present in
rapidly growing tissues, be released by livin `. cells
on injury, and be present in the growth -promoting
factors of embryo juice. The investigation falls
into three parts. In Part I the growth promoting
properties of various siubstances, including ribonucleic acid derivatives, are investigated with the
aid of a tissue culture test. In Part II the question of the release of such compounds b7 injured cells
is examined. In Part III the ribonucleic content of
tissues, especially rapidly growing tissues, is dealt
The results of this investigation have confirmed
the view that no other substances can stimulate the
growth of tissues in vitro so successfully as do extracts of embryonic tissue. It is improbable. however, that the effects of embryo extract can be attributed to any one individual constituent. Attempts to
separate any particular constituent, or group of constituents, have always resulted in loss of activity.
Wile embryo extracts are found to be rich in ribonucleoproteins, there is no reason to suppose that
their growth promoting activity is associated to any
great extent with the ribonucleoprotein fraction.
Of the non-embryonic material tested, the higher
protein-split -products have shown greatest growth
promoting power in stimulating nucleoprotein synthesis
in growing cells. The products of partial breakdown
of the nucleic acids have also shown activity.
Both these types of material have been found in
the products released by yeast cells injured by exposure to ultraviolet light. They may be released
either as the result of increased cell permeability
or as disintegratiori products of dead and dying cells,
and are responsible, in part at least, for the proliferation- promoting properties of extracts of ire
radiated yeast cells.
Ribonucleic acids have been demonstrated in all
mammalian tissues tested. Tn many tissues the amount
of cytoplasmic ribonucleic acid is greater than the
amount of nuclear desoxyribonucleic acid. When adult
sheep tissues are compared with the corresponding
embryonic tissues, the ratio of ribonucleic acid
phosphorus to desoxyribonucleic acid phosphorus for
any given tissue is in most cases, of the same order
in the adult as in the embryo, although the total
amount of nucleic acid in the embryonic tissue is
higher than in the adult tissue.
A ribonucleic acid has been isolated from liver
and shown to be similar to yeast ribonucleic acid.
It is present in the cytoplasm of the liver cell. The
amount present in liver tissue under various conditions
has been ascertained.
Tumour tissues also contain ribonucleic acid.
The total nucleic acid content of tumours is variable,
but in most cases is of a high order.
Rapidly growing tissues, embryonic or neoplastic,
tend to be characterized by a high water content, a
high total nucleic acid content, and a low acid
soluble nucleotide content.