The cell cycle during oogenesis and early embryogenesis in Drosophila

Abstract

Abstract Although changes in gene expression play a large role in determination and differentiation, most organisms also employ variant cell cycles in order to achieve particular developmental goals. This strategy is used widely during Drosophila development. In this chapter we address how cell cycle regulation interfaces with development, focusing on Drosophila oogenesis and early embryogenesis. Five modified cell cycles occur during these developmental stages: meiosis to produce haploid gametes, endo cycles to produce polyploid cells, amplification to increase gene copy number, S/M cycles for rapid division, and S/G2/M cycles. In each case we discuss the coordination between developmental events and alteration of the cell cycle, and we review recent advances in defining the regulation of these variant cell cycles. The unique feature of meiosis during oogenesis is that progression through the meiotic cell cycle must be halted at specific points to permit oocyte differentiation. The endo cycle is used in specific tissues throughout plants and animals. Analysis of this cycle in Drosophila nurse cells and follicle cells has provided key insights into how endo cycles are initiated and terminated, as well as how parameters of this cycle can be adjusted to produce differential DNA replication and alterations in chromosome morphology. Amplification provides a powerful model for deciphering the control of initiation of DNA replication in metazoans. We describe specialized regulation required for S/M cycles and how developmental regulatory genes directly affect the cell cycle to insert a G2 phase during embryogenesis.