A Cyclin A—Myb-MuvB—Aurora B network regulates the choice between mitotic cycles and polyploid endoreplication cycles

Abstract

Endoreplication is a cell cycle variant that entails cell growth and periodic genome duplication without cell division, and results in large, polyploid cells. Cells switch from mitotic cycles to endoreplication cycles during development, and also in response to conditional stimuli during wound healing, regeneration, aging, and cancer. In this study, we use integrated approaches in Drosophila to determine how mitotic cycles are remodeled into endoreplication cycles, and how similar this remodeling is between induced and developmental endoreplicating cells (iECs and devECs). Our evidence suggests that Cyclin A / CDK directly activates the Myb-MuvB (MMB) complex to induce transcription of a battery of genes required for mitosis, and that repression of CDK activity dampens this MMB mitotic transcriptome to promote endoreplication in both iECs and devECs. iECs and devECs differed, however, in that devECs had reduced expression of E2F1-dependent genes that function in S phase, whereas repression of the MMB transcriptome in iECs was sufficient to induce endoreplication without a reduction in S phase gene expression. Among the MMB regulated genes, knockdown of AurB protein and other subunits of the chromosomal passenger complex (CPC) induced endoreplication, as did knockdown of CPC-regulated cytokinetic, but not kinetochore, proteins. Together, our results indicate that the status of a CycA—Myb-MuvB—AurB network determines the decision to commit to mitosis or switch to endoreplication in both iECs and devECs, and suggest that regulation of different steps of this network may explain the known diversity of polyploid cycle types in development and disease.

An RNAi Screen for Genes Required for Growth ofDrosophilaWing Tissue

“…It is known that the Lin52 protein is required for the Myb subunit to associate with the core of the MMB transcription factor complex (Andrejka et al 2011; Guiley et al 2015; Guiley et al 2018). This lin-52 phenotype is, therefore, consistent with our previous finding that knockdown of Myb switches wing and other cells to endoreplication (Rotelli et al 2019). Similar to Myb knockdown, it is likely that knockdown of lin-52 impairs the induction of mitotic gene expression by the MMB and promotes a switch to endoreplication cycles that skip mitosis (Rotelli et al 2019).…”

“…This lin-52 phenotype is, therefore, consistent with our previous finding that knockdown of Myb switches wing and other cells to endoreplication (Rotelli et al 2019). Similar to Myb knockdown, it is likely that knockdown of lin-52 impairs the induction of mitotic gene expression by the MMB and promotes a switch to endoreplication cycles that skip mitosis (Rotelli et al 2019). Knockdown of βNACtes6 or lin-52 also reduced the area of the L3-L4 intervein region in adult wings, suggesting that tissue growth through an increase in cell size did not fully compensate for growth by cell proliferation (Figure 2F, K, Table 2).…”

“…The MMB induces the periodic cell cycle expression of genes that are important for M phase and cytokinesis (Georlette et al 2007; Schmit et al 2007; Wen et al 2008; Debruhl et al 2013; Fischer et al 2016). We had found previously that knockdown of the Myb subunit of the MMB in the wing impairs expression of mitotic genes and results in a switch to a polyploid growth program, which, similar to lin-52 knockdown, resulted in longer wing hairs and reduced tissue mass in the adult wing (Rotelli et al 2019). The similar phenotype of Myb and lin-52 knockdown makes sense in the context of recent structure-function studies that indicate that Lin52 is required for the activating Myb subunit to associate with the MuvB core (Andrejka et al 2011; Guiley et al 2018).…”

“…We recently conducted a candidate shRNA screen of 240 genes, which RNA-Seq had shown are expressed at lower levels in endoreplicating cells in culture. This candidate screen showed that knockdown of genes in a CycA – Myb – Aurora B pathway induces cells in the wing and other tissues to switch to an alternative endoreplication growth program (Rotelli et al 2019). Here, we report the results of a random screen of 5,260 additional shRNA strains, which has identified 18 genes whose knockdown impairs wing growth.…”

Rif1 Functions in a Tissue-Specific Manner To Control Replication Timing Through Its PP1-Binding Motif

“…Follicle cells undergo three endocycles, resulting in a ploidy of 16C. Previous work has shown that there are distinct changes in genome regulation during the endocycle, including a global decrease in transcription, decrease in E2F1 target gene expression, and acquisition of endocycle-specific ORC binding sites (Maqbool et al 2010;Sher et al 2012;Hua et al 2018;Rotelli et al 2019). Therefore, we hypothesized that follicle cell RT may be influenced by this developmentally regulated cell cycle transition.…”