The Role of Chibby Family Members in Spermatogenesis and Male Fertility

PD/PI：Takemaru，Ken-Ichi 7.项目摘要 纤毛是进化上保守的微管结构，从顶端细胞表面突出， 执行重要的生物功能，从信号传导到流体运动。精子鞭毛 是一种经过改造的能动纤毛，对卵子的运动和受精至关重要。因此，异常精子 鞭毛是男性不育的主要原因之一。虽然不完全等同，但类似的 机制被认为在鞭毛发生和纤毛发生期间起作用。纤毛发生缺陷与 与人类疾病，如原发性纤毛运动障碍，纤毛病，许多男性患者， 也显示出生育问题。尽管世界范围内的研究努力，以阐明纤毛蛋白的作用，在这些 尽管存在一些疾病，但对它们在男性生育力方面的生理作用仍然知之甚少。我们之前已经证明， 缺乏关键纤毛蛋白Chibby 1（Cby 1）的小鼠表现出纤毛病表型。分子上，Cby 1与 与膜结合BAR结构域蛋白，称为Cby 1-interacting BAR domain containing 1和2（ciBAR 1 和2，以前称为FAM 92 A和B），以促进纤毛发生。最近，我们发现一个Cby家族 Cby 1-Like（Cby 1 L，也称为Cby 3）在睾丸中大量表达。 有趣的是，Cby 1 L定位于纤维环，即位于中段/主段的基于隔蛋白的环状结构 (MP/PP）精子尾部的连接处。为了深入了解Cby 1 L在体内的功能， 精子发生，我们创造了Cby 1 L-/-小鼠，发现雄性小鼠完全不育，大多数 在MP/PP交界处显示扭结尾部的精子。奇怪的是，在Cby 1 L-/-小鼠的精子中， 存在，但未能在MP/PP交界处停止，并进入PP。虽然环是紧密的 在Cby 1 L-/-精巢中，环部分与鞭毛分离 这表明Cby 1 L参与了将环锚定到膜上。符合本 假设，我们发现Cby 1 L与ciBAR 1以及环隔蛋白SEPT 4物理相互作用。 此外，我们发现ciBAR 1定位于纤维环，ciBAR 1-/-雄性小鼠不育，产生 尾巴弯曲的精子总的来说，我们的初步数据表明了一个令人兴奋的工作模型，其中Cby 1 L在 与ciBAR 1的复合物在其尾部迁移期间将环稳定地锚定到鞭毛膜， 可能通过膜成形和收缩将其精确地定位在MP/PP接合处。这个项目的总体目标是 目的是了解Cby 1 L及其结合蛋白在精子发生和雄性不育中的分子作用。 生育为了实现这一目标，我们提出了以下具体目标：1）研究Cby 1 L在 使用Cby 1 L-/-小鼠模型的鞭毛发生; 2）研究ciBAR 1参与鞭毛发生， 雄性生育力;和3）确定新的Cby 1 L结合蛋白，并表征其功能在鞭毛发生。 我们预计，我们提出的研究将揭示一种新的机制， 纤毛蛋白对精子尾部的区室化。

PD/PI: Takemaru, Ken-Ichi 7. PROJECT SUMMARY Cilia are evolutionarily conserved microtubule-based structures that protrude from the apical cell surface to perform important biological functions, ranging from signal transduction to fluid movement. The sperm flagellum is a modified motile cilium that is essential for locomotion and fertilization of the egg. As such, abnormal sperm flagella are one of the leading causes of male infertility. Although not completely equivalent, analogous mechanisms are thought to operate during flagellogenesis and ciliogenesis. Defective ciliogenesis is associated with human disorders, known as ciliopathies, such as primary ciliary dyskinesia, and many of the male patients also show fertility issues. Despite worldwide research efforts to elucidate the role of ciliary proteins in these diseases, their physiological roles in male fertility remain poorly understood. We previously demonstrated that mice lacking the key ciliary protein Chibby1 (Cby1) exhibit ciliopathy phenotypes. Molecularly, Cby1 interacts with membrane-binding BAR domain proteins, called Cby1-interacting BAR domain-containing 1 and 2 (ciBAR1 and 2, formerly known as FAM92A and B), to facilitate ciliogenesis. More recently, we found that a Cby family member, Cby1-Like (Cby1L, also known as Cby3), is expressed abundantly and exclusively in the testis. Interestingly, Cby1L localizes to the annulus, a septin-based ring structure at the midpiece/principal piece (MP/PP) junction in the sperm tail, in the testis. To gain insight into the in vivo function of Cby1L during spermatogenesis, we created Cby1L-/- mice and found that male mice are completely infertile with the majority of sperm showing kinked tails around the MP/PP junction. Curiously, in the sperm from Cby1L-/- mice, the annulus is present but fails to stop at the MP/PP junction and progresses into the PP. Although the annulus is tightly bound to membranes during its migration, in Cby1L-/- testis, the annulus is partially detached from the flagellar membrane, suggesting that Cby1L is involved in anchoring the annulus to the membrane. Consistent with this hypothesis, we found that Cby1L physically interacts with ciBAR1 as well as the annulus septin SEPT4. Furthermore, we found that ciBAR1 localizes to the annulus, and ciBAR1-/- male mice are infertile, producing sperm with kinked tails. Collectively, our preliminary data suggest an exciting working model in which Cby1L in a complex with ciBAR1 stably anchors the annulus to flagellar membranes during its caudal migration and precisely positions it at the MP/PP junction likely via membrane shaping and constriction. The overall goal of this application is to understand the molecular roles of Cby1L and its binding proteins in spermatogenesis and male fertility. To achieve this goal, we propose the following Specific Aims: 1) Investigate the role of Cby1L in flagellogenesis using a Cby1L-/- mouse model; 2) Investigate the involvement of ciBAR1 in flagellogenesis and male fertility; and 3) Identify novel Cby1L-binding proteins and characterize their functions during flagellogenesis. We anticipate that our proposed research will unravel a novel mechanism underlying the proper compartmentalization of the sperm tail by ciliary proteins.