Mutations in Drosophila Greatwall/Scant Reveal Its Roles in Mitosis and Meiosis and Interdependence with Polo Kinase

Abstract

Polo is a conserved kinase that coordinates many events of mitosis and meiosis, but how it is regulated remains unclear. Drosophila females having only one wild-type allele of the polo kinase gene and the dominant Scant mutation produce embryos in which one of the centrosomes detaches from the nuclear envelope in late prophase. We show that Scant creates a hyperactive form of Greatwall (Gwl) with altered specificity in vitro, another protein kinase recently implicated in mitotic entry in Drosophila and Xenopus. Excess Gwl activity in embryos causes developmental failure that can be rescued by increasing maternal Polo dosage, indicating that coordination between the two mitotic kinases is crucial for mitotic progression. Revertant alleles of Scant that restore fertility to polo–Scant heterozygous females are recessive alleles or deficiencies of gwl; they show chromatin condensation defects and anaphase bridges in larval neuroblasts. One recessive mutant allele specifically disrupts a Gwl isoform strongly expressed during vitellogenesis. Females hemizygous for this allele are sterile, and their oocytes fail to arrest in metaphase I of meiosis; both homologues and sister chromatids separate on elongated meiotic spindles with little or no segregation. This allelic series of gwl mutants highlights the multiple roles of Gwl in both mitotic and meiotic progression. Our results indicate that Gwl activity antagonizes Polo and thus identify an important regulatory interaction of the cell cycle.

Greatwall Kinase Is Required for Meiotic Maturation in Porcine Oocytes1

“…It has been shown that GWL accelerates mitotic progression in various cell types, including those of Xenopus, Drosophila, and human [11,[13][14][15][16][17]. Therefore, we researched whether overexpression of GWL would induce meiotic resumption in porcine oocytes.…”

“…Depletion of GWL from interphase prevents entry into M phase, whereas overexpression of GWL accelerates entry into M phase in several species, including Drosophila, Xenopus, and human [11][12][13][14][15][16][17]. Moreover, depletion of GWL from mitotic egg extracts leads to exit from M phase by activation of PP2A [12,18].…”

The spindle pole body plays a key role in controlling mitotic commitment in the fission yeast Schizosaccharomyces pombe

“…Thus PP2A is a good candidate for the Greatwall antagonist. In Drosophila, Greatwall (gwl) antagonizes Polo kinase and recessive gwl mutants delay mitotic commitment, suggesting that Greatwall involvement in feedback control is likely to be conserved across species [29,30]. Thus there is much yet to learn about feedback loop amplification and it will be important to test the insights gained in one system in others to differentiate between universal elements of cell cycle control and specific adaptations to the demands of particular lifestyles.…”

α-endosulfine (ENSA) regulates exit from prophase I arrest in mouse oocytes

“…26,28,36,39,40,[45][46][47] Starfish and Drosophila have only one MASTL/Greatwall substrate, and the pig ENSA gene has a premature stop codon, such that porcine cells would not express functional ENSA protein. 40 Xenopus oocytes may rely solely or primarily on ARPP19 to regulate exit from prophase I arrest, 36,37 while the data here clearly indicate that ENSA is important for exit from prophase I arrest in mouse oocytes.…”