The role of the fungal STRIPAK complex in hyphal fusion and sexual development

Striatin相互作用的磷酸酶和激酶(STRIPAK)复合体在真菌和动物中保守。在丝状子囊菌中，STRIPAK复合体被发现对菌丝融合和子实体发育是必不可少的。大孢链霉菌中的STRIPAK同源基因有：PRO11(Striatin)、PRO22(STRIP1/2)、PRO45(SLMAP)、丝氨酸-苏氨酸磷酸酶支架亚基PP2AA、催化亚基SmPP2Ac1和激酶激活剂SmMOB3。与哺乳动物不同，真菌只包含一个条纹蛋白基因，因此是研究STRIPAK复合体细胞功能的良好模型。最近，我们进行了PRO11和SmMOB3下拉实验，并对可能的相互作用伙伴进行了LC-MS数据分析。一个未知的蛋白质被鉴定为具有很高可信度的推测的PRO11相互作用伙伴，命名为STRIPAK复合体相互作用蛋白1(SCI1)。SCI1是小螺旋(CC)结构域(S)的同源基因，含有在酵母、果蝇和哺乳动物的STRIPAK复合体中发现的蛋白质。在大孢子链霉菌中，SCI1基因的缺失揭示了其在细胞-细胞融合和性发育中的作用，并且在体内发现SCI1与核膜上的其他STRIPAK组分相互作用和共定位。因此，SCI1可以被认为是大孢子菌STRIPAK复合体的核心成分，我们证明了我们的蛋白质组学方法对于鉴定STRIPAK组分和效应物是有用的。对来自PRO11、SmMOB3和SCI1下拉实验的LCMS数据的进一步详细分析表明，核孔复合体的三种蛋白质、生发中心激酶MO25/HYM1的激活剂以及参与磷脂生物合成和运输的四种蛋白质显著富含。这些数据表明，STRIPAK复合体可能在激酶信号通路和磷脂信号通路中发挥作用。此外，核孔复合体蛋白可能作为连接STRIPAK复合体和核膜的锚。或者，核孔复合体的成分可能通过STRIPAK相关的激酶和PP2A磷酸酶而受到磷酸化和去磷酸化事件的调节。因此，通过研究STRIPAK复合体的这些新的相互作用伙伴，我们旨在了解STRIPAK复合体在真菌有性发育和细胞融合中的作用。此外，这些研究也可能有助于破译STRIPAK复合体在高等真核生物中的功能。

Striatin-interacting phosphatase and kinase (STRIPAK) complex is conserved in fungi and animals. In the filamentous ascomycete Sordaria macrospora, STRIPAK complex has been found to be essential for hyphal fusion and fruiting-body development. The STRIPAK orthologues in S. macrospora are PRO11 (striatin), PRO22 (STRIP1/2), PRO45 (SLMAP), the serine-threonine phosphatase scaffolding subunit PP2AA, catalytic subunit SmPP2Ac1, and kinase activator SmMOB3. Unlike mammals, fungi comprise only one striatin gene and are therefore good models to study the cellular function of the STRIPAK complex. Recently, we performed PRO11 and SmMOB3 pull-down experiments coupled to liquid chromatography and mass spectrometry (LCMS) and analyzed the LCMS data for putative interaction partners. An uncharacterized protein was identified as putative PRO11 interaction partner with very high confidence, and was named STRIPAK complex interactor 1 (SCI1). SCI1 is an orthologue of small coiled-coil (CC) domain(s) containing proteins found in STRIPAK complexes in yeasts, fruit fly, and mammals. Deletion of sci1 revealed its role in cell-cell fusion and sexual development in S. macrospora, and SCI1 was found to interact and co-localize with other STRIPAK components at the nuclear envelope in vivo. Thus, SCI1 can be considered as a core component of the S. macrospora STRIPAK complex and we proved that our proteomics approach is useful to identify STRIPAK components and effectors. Further detailed analysis of LCMS data from PRO11, SmMOB3, and SCI1 pull-down experiments showed significant enrichment of three proteins of the nuclear pore complex, the activator of germinal center kinases MO25/HYM1, and four proteins involved in phospholipid biosynthesis and transport. These data suggested that the STRIPAK complex may play a role in kinase signaling pathways and in phospholipid signaling. Moreover, nuclear pore complex proteins may act as anchors that link the STRIPAK complex to the nuclear envelope. Alternatively, components of the nuclear pore complex may be regulated by phosphorylation and dephosphorylation events via STRIPAK associated kinases and the PP2A phosphatase. Thus, by studying these new interaction partners of the STRIPAK complex, we aim to understand the role of STRIPAK complex in sexual development and cell fusion in fungi. Beside, these investigations may also help to decipher the function of STRIPAK complexes in higher eukaryotes.