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

在我们的社会中，不孕症是一个日益严重的问题，大约15%的夫妇都想要孩子。男性不育的一个常见原因是无法形成功能正常的精子头。在大多数情况下，潜在病理缺陷的最终原因尚不清楚。然而，最近的研究表明，LINC复合物可能在这方面发挥关键作用。LINC复合物是核包膜桥接复合物，介导核结构与细胞骨架的直接连接。它们被发现是核迁移、定位和锚定以及减数分裂染色体运动的关键。在先前的研究中，我们可以证明减数分裂后细胞形成独特的LINC复合物，其表现出与成形过程密切相关的显着行为。这反过来表明它们在精子头形成和核伸长中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缺乏会导致产生严重缺陷和完全畸形的精子。目前项目的目的是进一步启发我们对精子中LINC复合物的实际组成，相互作用和功能的了解。鉴于此，我们将在第一个子项目中更深入地挖掘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复合物中的特定作用。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敲除小鼠模型来研究。另一个子课题是研究Sun1在精子发生过程中的特定功能。为此，我们将产生一种转基因小鼠系，使我们能够深入分析体内精子分化过程中Sun1的功能和行为。最后，我们希望分别利用野生型和缺乏Sun4和Sun5的精子来研究LINC复合物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.