MATERNAL mRNA AND PROTEIN SYNTHESIS IN THE EMBRYO

Abstract

According to the masked maternal messenger RNA hypothesis, a large part if not all the protein synthesis of early development is directed by mRNA already present in the cytoplasm of unfertilized eggs. This mRNA is supposed to be synthesized during oogenesis and stored in some unavailable form until some later time in development, when it is selectively associated with the translational machinery. To the indirect evidence, which is nevertheless very strong, there can now be added a direct proof of the hypothesis for the case of histone mRNA. The five main histones of sea urchin embryos are synthesized on small polyribosomes, directed in part by newly-synthesized messages that sediment as a group at about 9S. Some histone synthesis survives total transcription block, however, suggesting that maternal histone mRNA exists. In competition-hybridization experiments, the egg RNA is shown to contain sequences characteristic of functional, embryonic histone mRNA. The competing RNA is localized in ribonucleoprotein particles of egg homogenates that sediment at 20–40S. These same particles contain RNA that stimulates a cell-free heterologous system to synthesize sea urchin histones. The application of these facts to some problems of translation control and of development generally is discussed.

RNA synthesis in immature mouse oocyte development

“…In addition, as sug gested by amphibian studies (Davidson, 1968), a significant portion of the label probably represents informational RNA synthesized on the chromatin. It is noted also that Gross and Gross (1973) identified a maternal messenger RNA and the histone RNA product during echinodern development.…”

“…Normal development is controlled in part by sequential selective gene activation and repression (Markert and Ursprung, 1971) and it is possible that molecules from the cytoplasm are responsible for selective activation of genes. Nucleic acids possess adequate informa tional content to fulfill this role (Gross, 1973;Markert and Ursprung, 1971). Gross (1973) suggests that messenger RNA is the molecule with the ability to control differentiation with its assymetrical distribution within the embryo.…”

“…Nucleic acids possess adequate informa tional content to fulfill this role (Gross, 1973;Markert and Ursprung, 1971). Gross (1973) suggests that messenger RNA is the molecule with the ability to control differentiation with its assymetrical distribution within the embryo.…”

“…In every animal class RNA synthesis probably is evident during previtellogenic and lampbrush stages and is especially dramatic in amphibian and echinoderm oocytes (Davidson, 1968). That RNA synthesized during lampbrush stages is packaged and stored is demonstrated by hybrid ization studies with labelled precursor in the amphibian (Hough, et al, 1973) and competition-hybridization experiments in the sea urchin (Gross, et al, 1973). Presumably these molecules are used later in embryonic development although details of their utilization remain to be worked out.…”

Physical Implications of Pure Lovelock Geometry on Stellar Structure

“…The EGB theory finds support from string theory as the very same Lagrangian appears in the low energy effective action of heterotic string theory. [ 17 ] The Lovelock polynomial is the tensor‐only action that generates up to second order equations of motion. If the effects of a scalar field is incorporated with a tensor field then we must use the Horndeski [ 18 ] modification.…”