Germ cell-specific LINC complexes and their relevance for nuclear remodelling, shaping and fertility

不孕不育在我们的社会中是一个日益严重的问题，大约15%的夫妇打算生孩子。男性不育的一个常见原因是无法形成有功能的规则形状的精子头。在大多数情况下，潜在的病理缺陷的最终原因尚不清楚。然而，最近的研究表明，LINC复合体在这一背景下可能发挥关键作用。LINC复合体是一种核膜桥联复合体，它介导了核结构与细胞骨架的直接连接。它们被发现对核迁移、定位和锚定以及减数分裂染色体运动起着关键作用。在以前的研究中，我们可以证明减数分裂后的细胞形成独特的LINC复合体，表现出与形成过程密切相关的显着行为。这反过来表明，它们在精子头部形成和核延长方面起着至关重要的作用。这种作用的直接证据来自我们最近的研究，我们可以证明Sun4缺乏会引发严重缺陷和完全畸形的精子细胞的产生。目前这个项目的目的是进一步启发我们关于精子细胞中LINC复合体的实际组成、相互作用和功能的仍然支离破碎的知识。有鉴于此，我们在第一个子项目中想要更深入地挖掘Sun4的特定属性。我们将特别讨论它的拓扑和生化特征以及它在依赖Sun4的LINC复合体中的特殊作用。第二个子项目将针对Sun5的实际功能，我们打算用免疫组织化学和生化方法，特别是通过Sun5基因敲除的小鼠模型来探讨这一点。另一个子项目涉及SUN1在精子发生过程中的特定功能。为此，我们将建立一个转基因小鼠系，使我们能够深入分析SUN1在体内精子分化过程中的功能和行为。最后，我们想利用野生型以及分别缺乏Sun4和Sun5的精子细胞，来研究LINC复合体在膜间距中的假设作用。

Infertility is an increasing problem in our society and applies to approximately 15% of the couples that aim to have children. A frequent cause of male infertility is the inability to form functional regularly shaped sperm heads. In most cases the ultimate reason for the underlying pathological defects is unclear. Recent studies, however, indicate that LINC complexes could play a critical role in this context. LINC complexes are nuclear envelope bridging complexes that mediate a direct connection of nuclear structures with the cytoskeleton. They were found to be pivotal for nuclear migration, positioning and anchoring and for meiotic chromosome movements. In previous studies we could demonstrate that postmeiotic cells form unique LINC complexes showing a conspicuous behavior that closely correlates with the shaping process. This in turn suggests that they have a vital role in sperm head formation and nuclear elongation. Direct evidence for such a role came from our recent study where we could demonstrate that Sun4 deficiency provokes the generation of severely defective and entirely misshaped spermatids. The aim of the current project is now to further enlighten our still fragmentary knowledge about the actual composition, interaction and function of LINC complexes in spermatids. In light of this, we within a first subproject would like to dig deeper into the specific properties of Sun4. We in particular will address its topological and biochemical characteristics and its specific role within Sun4 dependent LINC complexes. A second subproject will be directed to the actual function of Sun5, which we intend to approach with immunohistochemical and biochemical methods and in particular also by means of a Sun5 knock out mouse model. Another subproject deals with the specific function of Sun1 during spermiogenesis. To this end we will generate a transgenic mouse line that will allow us to analyze in depth Sun1 function and behavior during sperm differentiation in vivo. Finally, we would like to make use of wildtype as well as Sun4 and Sun5 deficient spermatids, respectively, to survey the hypothesized role of LINC complexes in membrane spacing.