Department of Biology, Brandeis University, Waltham, MA 02454.
Department of Molecular and Biomedical Sciences, University of Maine, Orono, ME 04469.
Mol Biol Cell. 2024 Jun 1;35(6):ar85. doi: 10.1091/mbc.E23-11-0459. Epub 2024 Apr 24.
In response to pheromone extend a mating projection. This process depends on the formation of polarized actin cables which direct secretion to the mating tip and translocate the nucleus for karyogamy. Here, we demonstrate that proper mating projection formation requires the formin Bni1, as well as the actin nucleation promoting activities of Bud6, but not the formin Bnr1. Further, Bni1 is required for pheromone gradient tracking. Our work also reveals unexpected new functions for Bil2 in the pheromone response. Previously we identified Bil2 as a direct inhibitor of Bnr1 during vegetative cell growth. Here, we show that Bil2 has Bnr1-independent functions in spatially focusing Bni1-GFP at mating projection tips, and in vitro Bil2 and its binding partner Bud6 organize Bni1 into clusters that nucleate actin assembly. cells also display entangled Bni1-generated actin cable arrays and defects in secretory vesicle transport and nuclear positioning. At low pheromone concentrations, cells are delayed in establishing a polarity axis, and at high concentrations they prematurely form a second and a third mating projection. Together, these results suggest that Bil2 promotes the proper formation and timing of mating projections by organizing Bni1 and maintaining a persistent axis of polarized growth.
为了响应信息素,延伸交配投射。这个过程依赖于极化肌动蛋白电缆的形成,这些电缆将分泌物导向交配尖端,并将核移至核融合处。在这里,我们证明了正确的交配投射形成需要形成素 Bni1,以及 Bud6 的肌动蛋白成核促进活性,但不需要形成素 Bnr1。此外,Bni1 还需要用于信息素梯度跟踪。我们的工作还揭示了 Bil2 在信息素反应中的意想不到的新功能。之前我们确定 Bil2 是营养细胞生长过程中 Bnr1 的直接抑制剂。在这里,我们表明 Bil2 在空间聚焦 Bni1-GFP 在交配投射尖端具有与 Bnr1 无关的功能,并且在体外 Bil2 和其结合伴侣 Bud6 将 Bni1 组织成成核肌动蛋白组装的簇。Bil2 突变体还显示纠缠的 Bni1 生成的肌动蛋白电缆阵列和分泌小泡运输和核定位的缺陷。在低浓度的信息素下,Bil2 突变体细胞在建立极性轴方面延迟,而在高浓度下,它们过早地形成第二个和第三个交配投射。总之,这些结果表明 Bil2 通过组织 Bni1 并维持极化生长的持久轴来促进交配投射的正确形成和定时。