2 Growth and Cell Cycle Control in Drosophila

Abstract

Unicellular organisms tend to proliferate whenever environmental Conditions—nutrients, oxygen, temperature, etc.—permit, and they cease growth when one or another of these conditions throttles their metabolism. In such cells, the progress of the division cycle is generally tightly coupled to cell growth. In contrast, animal cells exist in physiologically controlled environments that are nearly always nutrient-rich, yet they proliferate selectively. Specific autocrine, paracrine, and endocrine signals stimulate or limit cell growth and proliferation according to rules that benefit the organism as a whole. Moreover, the division cycle in multicellular systems is not always growth-coupled. Some cell types, like neurons and oocytes, grow without dividing, whereas others, such as spermatocytes, early blastomeres, and neuroblasts, can divide many times with little or no growth. Thus, the controls for cell growth and cell-cycle progression, although overlapping, are not the same in animal cells. In this chapter, we discuss the various modes of cell cycling and cell growth that occur during Drosophila development, and we examine the relationship between these two processes.

OUTLINE OF CELL GROWTH AND PROLIFERATION DURING DROSOPHILA DEVELOPMENT
Growth-independent Cell Cycles in Embryogenesis
Careful descriptive studies of Drosophila from as long ago as the 1920s provide a rich literature on cell-cycle dynamics during development (Lee and Orr-Weaver 2003). The first cell cycles of embryogenesis are the female meiotic divisions, which are triggered by ovulation (Huettner 1924). Following meiosis and fertilization, the embryonic nuclei undergo 13 rapid mitotic divisions, which are driven by maternal proteins and mRNAs (Rabinowitz 1941; Foe and...