Rates of protein synthesis in whole and half embryos of the sea urchin

Abstract

Uptake and incorporation rates of 14C-valine, as measured by the activities of acid-soluble and insoluble fractions, were measured from fertilization to post-gastrula stages of the sea urchin, Lytechinus anamesus. The general pattern of the incorporation rate curve is a complex one consisting of an overall acceleration in rate from fertilization to or after gastrulation interrupted by declines and increases at specific pre-gastrular stages. The uptake rate similarly, although less rapidly, increases after fertilization and during cleavage; the subsequent course of the uptake curve is variable and may or may not resemble its companion incorporation rate curve. Incorporation rate as derived from a pulse measurement is assumed to be a function of both protein synthesis and transport rate of labeled amino acid and it is suggested that rates of protein synthesis may be more accurately reflected by the per cent incorporation, i.e., that percentage of the total labeled amino acid taken up which is incorporated. Per cent incorporation curves indicate two major periods of accelerated rates of protein synthesis: after fertilization through cleavage and shortly after hatching to a late mesenchyme blastula or early gastrula stage. A major decline occurs during ciliation and hatching, minor temporary declines occur at an early cleavage stage and possibly in the early gastrula. It is suggested that comparative levels of protein synthesis during development are pictured more accurately in the per cent incorporation curves; thus the rate of protein synthesis in the early blastula near the close of cleavage is close to the level attained much later during gastrulation. Incorporation rates of 14C-valine in half embryos, obtained by separation of animal and vegetal layers of cells at the 8-cell stage, were measured at times equivalent to early cleavage, late blastula, gastrula and post-gastrula stages. Incorporation rates are essentially similar in both types of embryos. A slightly higher rate of incorporation into vegetal halves during early cleavage may be due to a more rapid transport of the amino acid into the vegetal cells. Per cent incorporation values are approximately the same for animal and vegetal halves at early cleavage and the mesenchyme blastula or early gastrula period. Incorporation rates as well as per cent incorporation values of 14C-methionine were found to be identical in animal and vegetal regions of the fertilized egg through the first cleavage. It is concluded that rates of protein synthesis do not differ in animal and vegetal regions of the egg nor in animal and vegetal half embryos during the period of determination and early differentiation.