Macromolecular Changes Associated with the Growth of Crustacean Tissues

Tissue mass, rate of protein synthesis, content of ribosomal RNA and rates of synthesis of ribosomal RNA have been studied throughout the molting cycle in the midgut gland, epithelium, and somatic muscle in the land crab, Gecarcinns lateralis . In all tissues there is an increase in ribosomal RNA followed by an increase in the rate of synthesis of protein in the premolt period. Subsequently, the three tissues differed in that (a) in the midgut gland the level of ribosomal RNA and protein synthesis returned to the intermolt rates before ecdysis whether or not the mass of the tissue was increasing or decreasing; (b) ribosomal RNA and protein synthesis in epithelium reached a maximum at a time when epithelial cells reached a maximal size; subsequently, all three parameters decreased toward intermolt levels before ecdysis; (c) ribosomal RNA and protein synthesis reached a maximum in the premolt period in somatic muscle while the muscle was in fact decreasing in mass. Muscle ribosomes are very stable and appear to be conserved for weeks or months to be reused after ecdysis in a second burst of protein synthetic activity at the time when there is replacement and growth of new muscular tissue. The relation of these events with hormonal control of growth is discussed.