Dynamics of Endoreplication during Drosophila Posterior Scutellar Macrochaete Development

Abstract

Endoreplication is a variant type of DNA replication, consisting only of alternating G1 and S phases. Many types of Drosophila tissues undergo endoreplication. However, the timing and the extent to which a single endocycling macrochaete undergoes temporally programmed endoreplication during development are unclear. Here, we focused on the dynamics of endoreplication during posterior scutellar (pSC) macrochaete development. Quantitative analyses of C values in shaft cells and socket cells revealed a gradual rise from 8C and 4C at 8 hours after pupal formation (APF) to 72C and 24C at 29 hours APF, respectively. The validity of the values was further confirmed by the measurement of DNA content with a confocal laser microscope. BrdU incorporation assays demonstrated that shaft cells undergo four rounds of endoreplication from 18 to 29.5 hours APF. In contrast, socket cells undergo two rounds of endoreplication during the same period. Statistical analyses showed that the theoretical C values, based on BrdU assays, nearly coincide with the actually measured C values in socket cells, but not in shaft cells after 22 hours APF. These analyses suggest that socket cells undergo two rounds of endoreplication. However, the mechanism of endoreplication in the shaft cells may change from 22 hours APF, suggesting the possibility that shaft cells undergo two or four rounds of endoreplication during the periods. We also found that the timing of endoreplication differs, depending on the type of macrochaete. Moreover, endocycling in shaft cells of both the left and right sides of pSC bristle lineages occurs in the same pattern, indicating that the process is synchronized for specific types of macrochaete. Our findings suggest that endocycling in macrochaete cell lineages can be a model for understanding mechanisms of endoreplication at the single-cell level.

Dissecting, Fixing, and Visualizing the <em>Drosophila</em> Pupal Notum

“…The presented technique works well on the unwounded notum (Figure 1A-D), allowing for investigation of the development and homeostasis of the tissue, e.g., the formation of the polyploid mechanosensory bristle cells 18 , or the anterior to the posterior flow of epithelial cells 10 . This protocol is also applicable to a laser-ablated notum (Figure 1E-L), where the cellular response to injury can be analyzed live with endogenous fluorophores such as Histone2-EGFP (Figure 1B,F,J).…”

Dissecting, Fixing, and Visualizing the <em>Drosophila</em> Pupal Notum

“…The presented technique works well on the unwounded notum (Figure 1A-D), allowing for investigation of the development and homeostasis of the tissue, e.g., the formation of the polyploid mechanosensory bristle cells 18 , or the anterior to the posterior flow of epithelial cells 10 . This protocol is also applicable to a laser-ablated notum (Figure 1E-L), where the cellular response to injury can be analyzed live with endogenous fluorophores such as Histone2-EGFP (Figure 1B,F,J).…”

Control of e2f1 and PCNA by Drosophila transcription factor DREF

“…E2F1 also plays important roles in cell cycle progression in Drosophila endocycling Maqbool et al, 2010;Royzman et al, 1997), characterized by lacks of G2 and M phase (Edgar and Orr-Weaver, 2001;Lee et al, 2009). Thus, the affected cells increase their DNA content and grow larger in many Drosophila differentiated tissues, such as shaft and socket cells of mechanosensory bristles (Audibert et al, 2005;Hartenstein and Posakony, 1989;Kawamori et al, 2012;Salle et al, 2012) and salivary glands, which undergo multiple rounds of endoreplication to facilitate high metabolic activity (Edgar and Orr-Weaver, 2001). CycE is required for cell cycle progression in both mitotic and endocycle divisions (Knoblich et al, 1994;Richardson et al, 1995).…”