Chapter 4 The Cocoonase Zymogen Cells of Silk Moths: A Model of Terminal Cell Differentiation For Specific Protein Synthesis

Abstract

Publisher Summary This chapter discusses the zymogen cell differentiation for specific protein synthesis. Development of terminally differentiated cells specialized for specific protein synthesis involves the sequential and coordinated occurrence of several steps. Some of these are: differential mitosis, morphogenesis, mitosis or polyploidization, elaboration of an appropriate cytoplasm, synthesis of the specific cell product at a low and then high rate, and finally turning off or the modulation of specific synthesis. Continuous increase in specific protein synthesis during phase I and II is quite significant. If the specific gene is very active in transcription, differential stability would lead to mRNA accumulation. Thus, the stability of the mRNA can account for the marked progressive increase in translation, within phase II, without the necessity of postulating a parallel increase in the transcriptional activity. The absolute increase in specific protein synthesis during phase I is much slower, suggesting that accumulation and perhaps specific gene transcription is occurring more slowly at that time. Assuming that protein synthesis is proportional to mRNA content, the increase in protein synthesis during phase II measures the rate, at which specific mRNA accumulates in the system. This rate of accumulation is compatible with the existence of a single copy of the differentiation-specific gene per genome.