Notch-Delta signaling induces a transition from mitotic cell cycle to endocycle inDrosophilafollicle cells (original) (raw)
Related papers
Current Biology, 2004
by dephosphorylating the inhibitory sites. As a consequence, cells are propelled into mitosis. We have pre-Seattle, Washington 98195-7350 viously described the role of Notch signaling in downregulating string at stage 6 of oogenesis to allow the cells to transit into the endocycle [1]. The 4.9 kb and 6.4 kb Summary elements found in the 50 kb-long string promoter drive string expression in follicle cells from germarium to During Drosophila oogenesis, Notch function regulates the transition from mitotic cell cycle to endocycle stage 3 and from stage 4 to stage 6, respectively (Figure 1B). The Notch-Delta cascade achieves the tight down-in follicle cells at stage 6 [1, 2]. Loss of either Notch function or its ligand Delta (Dl) disrupts the normal regulation of the 6.4 kb element at stage 6, when the mitotic-to-endocycle transition takes place (Figure 1C, transition; this disruption causes mitotic cycling to continue and leads to an overproliferation phenotype red channel; [1]). A string rescue construct that contains 15.3 kb of the string promoter restores only the early [1, 2]. In this context, the only known cell cycle component that responds to the Notch pathway is String/ string expression pattern between germarium and stage 1-2 egg chambers (because of the 4.9 kb element) but Cdc25 (Stg), a G2/M cell cycle regulator [1]. We found that prolonged expression of string is not sufficient to does not contain the control element active between stages 3 and 6 (the 6.4 kb element) (Figure 1B; [1]). keep cells efficiently in mitotic cell cycle past stage 6, suggesting that Notch also regulates other cell cycle Although stg clones produce cells arrested in G2, the mutant nuclei were larger than in the wild-type cells components in the transition. By using an expression screen, we found such a component: Fizzy-related/ when stg clones were produced in the background of the 15.3 kb rescue construct (Figures S1A and S1AЈ in Hec1/Cdh1 (Fzr), a WD40 repeat protein. Fzr regulates the anaphase-promoting complex/cyclosome (APC/C) the Supplemental Data available with this article online; [1]). Furthermore, the mutant clones are half the size of and is expressed at the mitotic-to-endocycle transition in a Notch-dependent manner. Mutant clones of sister clones (Figure S1A; [1]), suggesting that the mutant cells stop division and possibly enter endocycle Fzr revealed that Fzr is dispensable for mitosis but essential for endocycles. Unlike in Notch clones, in too early. If downregulating String leads the follicle cells to enter an endocycle rather than to completely arrest, Fzr mutant cells mitotic markers are absent past stage 6. Only a combined reduction of Fzr and ectopic Stg then the sole role of Notch, which downregulates string expression at the switch, is to act on string to promote expression prolongs mitotic cycles in follicle cells, suggesting that these two cell cycle regulators, Fzr endocycling. If this is the case, string expression is the only limiting factor in the mitotic-to-endocycle transi-and Stg, are important mediators of the Notch pathway in the mitotic-to-endocycle transition. tion. Also, because ectopic expression of stg in Drosophila embryos and discs is capable of driving cells blocked in G2 into mitosis [8], continuous string expres-Results and Discussion sion should keep most cells in the mitotic phase. We overexpressed stg (either with a heat-shock-In Drosophila, nurse and follicle cells in the adult ovary endocycle in a regulated manner (Figure 1A; [3]; re-inducible promoter or with one or two copies of the UAS-stg transgene via the flip-out Gal4 system [9]) to viewed in [4, 5]). It has been suggested that endocycling requires the loss of M-phase cyclin-dependent kinase analyze whether String is sufficient to prolong division of follicle cells past stage 6. Overexpression of string (Cdk) activity and oscillations in the activity of S-phase with a transgene driven by a heat-shock promoter did Cdk [4, 6]. In Drosophila follicle cells, the function of the not show any ectopic Cyclin B or Phospho-Histone 3 Notch pathway in the mitotic-to-endocycle transition (PH3) expression (Figure 1E). With one copy of the UAS has been well established [1, 2]. Lack of Notch activity string transgene, we rarely observed prolonged mitotic in Drosophila follicle cells leads to prolonged mitosis divisions in follicle cells past stage 6, except in the posat the expense of endocycles, suggesting that Notch terior region, where 10% (Figure 1E) of the clones that functions in this context as a tumor suppressor [1, 7].
Notch Signaling and Developmental Cell-Cycle Arrest in Drosophila Polar Follicle Cells
Molecular Biology of the Cell, 2009
Temporal and spatial regulation of cell division is critical for proper development of multicellular organisms. An important aspect of this regulation is cell-cycle arrest, which in many cell types is coupled with differentiated status. Here we report that the polar cells—a group of follicle cells differentiated early during Drosophila oogenesis—are arrested at G2 phase and can serve as a model cell type for investigation of developmental regulation of cell-cycle arrest. On examining the effects of String, a mitosis-promoting phosphatase Cdc25 homolog, and Notch signaling in polar cells, we found that misexpression of String can trigger mitosis in existing polar cells to induce extra polar cells. Normally, differentiation of the polar cells requires Notch signaling. We found that the Notch-induced extra polar cells arise through recruitment of the neighboring cells rather than promotion of proliferation, and they are also arrested at G2 phase. Notch signaling is probably involved in...
Development, 1996
During early development, there are numerous instances where a bipotent progenitor divides to give rise to two progeny cells with different fates. The Notch gene of Drosophila and its homologues in other metazoans have been implicated in many of these cell fate decisions. It has been argued that the role of Notch in such instances may be to maintain cells in a precursor state susceptible to specific differentiating signals. This has been difficult to prove, however, due to a lack of definitive markers for precursor identity. We here perform molecular and morphological analyses of the roles of Notch in ovarian follicle cells during Drosophila oogenesis. These studies show directly that constitutively active Notch arrests cells at a precursor stage, while the loss of Notch function eliminates this stage. Expression of moderate levels of activated Notch leads to partial transformation of cell fates, as found in other systems, and we show that this milder phenotype correlates with a pro...
Development, 2007
The specification of polar, main-body and stalk follicle cells in the germarium of the Drosophila ovary plays a key role in the formation of the egg chamber and polarisation of its anterior-posterior axis. High levels of Notch pathway activation, resulting from a germline Delta ligand signal, induce polar cells. Here we show that low Notch activation levels, originating from Delta expressed in the polar follicle cells, are required for stalk formation. The metalloprotease Kuzbanian-like, which cleaves and inactivates Delta, reduces the level of Delta signaling between follicle cells, thereby limiting the size of the stalk. We find that Notch activation is required in a continuous fashion to maintain the polar and stalk cell fates. We further demonstrate that mutual antagonism between the Notch and JAK/STAT signaling pathways provides a crucial facet of follicle cell patterning. Notch signaling in polar and main-body follicle cells inhibits JAK/STAT signaling by preventing STAT nuclear translocation, thereby restricting the influence of this pathway to stalk cells. Conversely, signaling by JAK/STAT reduces Notch signaling in the stalk. Thus, variations in the levels of Notch pathway activation, coupled with a continuous balance between the Notch and JAK/STAT pathways, specify the identity of the different follicle cell types and help establish the polarity of the egg chamber.
During Drosophila oogenesis, follicle cells sequentially undergo three distinct cell-cycle programs: the mitotic cycle, endocycle, and gene amplification. Notch signaling plays a central role in regulating follicle-cell differentiation and cell-cycle switches; its activation is essential for the mitotic cycle/endocycle (M/E) switch. Cut, a linker between Notch signaling and cell-cycle regulators, is specifically downregulated by Notch during the endocycle stage. To determine how signaling pathways coordinate during the M/E switch and to identify novel genes involved in follicle cell differentiation, we performed an in vivo RNAi screen through induced knockdown of gene expression and examination of Cut expression in follicle cells. We screened 2205 RNAi lines and found 33 genes regulating Cut expression during the M/E switch. These genes were confirmed with the staining of two other Notch signaling downstream factors, Hindsight and Broad, and validated with multiple independent RNAi lines. We applied gene ontology software to find enriched biological meaning and compared our results with other publications to find conserved genes across tissues. Specifically, we found earlier endocycle entry in anterior follicle cells than those in the posterior, identified that the insulin-PI3K pathway participates in the precise M/E switch, and suggested Nejire as a cofactor of Notch signaling during oogenesis.
Drosophila Inducer of MEiosis 4 (IME4) is required for Notch signaling during oogenesis
Proceedings of the National Academy of Sciences, 2011
N 6 -methyladenosine is a nonediting RNA modification found in mRNA of all eukaryotes, from yeast to humans. Although the functional significance of N 6 -methyladenosine is unknown, the Inducer of MEiosis 4 ( IME4 ) gene of Saccharomyces cerevisiae , which encodes the enzyme that catalyzes this modification, is required for gametogenesis. Here we find that the Drosophila IME4 homolog, Dm ime4 , is expressed in ovaries and testes, indicating an evolutionarily conserved function for this enzyme in gametogenesis. In contrast to yeast, but as in Arabidopsis , Dm ime4 is essential for viability. Lethality is rescued fully by a wild-type transgenic copy of Dm ime4 but not by introducing mutations shown to abrogate the catalytic activity of yeast Ime4, indicating functional conservation of the catalytic domain. The phenotypes of hypomorphic alleles of Dm ime4 that allow recovery of viable adults reveal critical functions for this gene in oogenesis. Ovarioles from Dm ime4 mutants have fused...