How do Fbxo7 and PI31 control sperm morphogenesis and male fertility?

精子细胞是人体内最小的细胞，为了游得更快，精子细胞几乎排出了所有的细胞内容物。因此，成熟精子的产生可能涉及所有哺乳动物生物学中最激进的细胞形状变化。随着精子的发育，它们在支持和塑造精子的哺育细胞(支持细胞)内被拖入深深的凹陷(“隐窝”)。在其中，发育中的精子细胞准备好清除细胞质，并将其打包以供支持细胞处理。当精子意识到自己的最终形状时，它们被推回隐窝，最终释放为自由生活的成熟精子细胞。到目前为止，人们对协调这种转变并控制每个细胞如何塑造成最终形状的过程知之甚少。我们最近发现，一种名为Fbxo7的蛋白质对于精子在呈现这种流线型形状的过程中的精确时间重塑至关重要。在缺乏Fbxo7的雄性小鼠中，精子细胞正常发育，直到它们进入隐窝--然而，这些细胞从未离开过隐窝，而是一下子全部死亡。这表明，Fbxo7是制造精子的细胞重塑步骤所必需的。我们知道，Fbxo7在维持线粒体的功能--为细胞提供能量--以及处理有缺陷的线粒体方面发挥了作用。Fbxo7通过在其他“靶”蛋白质上添加一个称为泛素的小标签来实现其许多功能。这种泛素标签通常会导致目标蛋白被一种名为蛋白酶体的大型降解酶处理掉，但在某些情况下，它可以改变目标蛋白的功能或在细胞内移动它。Fbxo7还与一种名为PI31的伙伴蛋白相互作用，PI31将蛋白酶体连接到马达蛋白上，使它们在细胞内移动。我们的发现表明，Fbxo7在其伴侣PI31的帮助下或在其帮助下将泛素添加到靶蛋白中，可能是在精子重塑的最后阶段调节线粒体和/或蛋白酶体在细胞内运输的关键因素。我们的关键目标是：1.找出缺乏Fbxo7和PI31的男性睾丸中的问题-线粒体是否碎裂或变形，它们是否被带到细胞内的正确位置，以及它们是否正常工作？或者，蛋白酶体的本地化有问题吗？我们将使用荧光显微镜和电子显微镜结合每个过程的标记染色来研究这一点。为了确定Fbxo7在正常睾丸中的生化作用-它将泛素附着到什么上，这有什么影响？它需要PI31的帮助吗？当精子被塑造时，什么蛋白质与蛋白酶体相关，这是如何由Fbxo7和PI31控制的。我们将通过比较缺乏Fbxo7和PI31的小鼠细胞中泛素标记的蛋白和蛋白酶体相关蛋白来研究这一点。从纯科学和医学角度来看，了解这些事件是如何发生的都很重要-例如，了解Fbxo7的功能可能有助于我们理解并最终治疗一些没有精子的不孕不育患者。相反，选择性地干扰睾丸中的Fbxo7功能可能成为男性避孕新方法的基础。Fbxo7在其他组织中也很重要：许多不同类型的细胞，如红细胞和神经细胞，也会经历重塑以改变其形状，Fbxo7缺乏症也与贫血和帕金森氏症等神经疾病有关。了解Fbxo7和PI31是如何控制睾丸细胞形状的，可能会揭示它们在这些其他疾病中的作用(S)。

Sperm cells are the smallest cells in the body, having shed virtually all of their cellular contents in order to swim faster. The production of mature sperm thus involves perhaps the most radical changes in cellular shape in all of mammalian biology. As sperm cells develop, they are dragged into deep indentations ("crypts") within nurse cells (Sertoli cells) that support and sculpt them. Therein, developing sperm cells make ready their cytoplasm for elimination, and package it up for disposal by the Sertoli cells. As the sperm realise their final shape, they are pushed back out of the crypts, and finally released as free-living, mature sperm cells. As yet, little is understood about the processes that coordinate this transformation and control how each cell is moulded into its final shape. We recently discovered that a protein called Fbxo7 is critical for sperm remodelling at a precise time in the process of assuming this streamlined shape. In male mice that lack Fbxo7, sperm cells develop normally up to the point where they enter the crypts - however the cells never leave the crypts and instead all die at once. This shows that Fbxo7 is necessary for the cellular remodelling steps to make a sperm. We know that Fbxo7 plays a role in maintaining the function of mitochondria - which supply cells with energy - and in disposing of defective mitochondria. Fbxo7 performs many of its functions by adding a small tag, called ubiquitin, onto other "target" proteins. This ubiquitin tag usually causes the target proteins to be disposed of by a large degrading enzyme called the proteasome, but in some cases, it can alter the target protein's function or move it around the cell. Fbxo7 also interacts with a partner protein called PI31 that attaches proteasomes to motor proteins to move them around within a cell. Our findings suggest that the addition of ubiquitin to target proteins by Fbxo7, with or without the help of its partner PI31, is likely to be akey factor in regulating mitochondria and/or proteasome trafficking inside the cell during the final phase of sperm remodelling.Our key goals are:1. To find out what is going wrong in the testes of males lacking Fbxo7 and PI31 - are the mitochondria fragmented or deformed, are they being carried to the right location within the cell, and are they working normally? Alternatively, is there a problem with proteasome localisation? We will investigate this using fluorescence microscopy and electron microscopy in conjunction with staining for markers of each of these processes.2. To identify what Fbxo7 is doing biochemically in normal testes - what is it attaching ubiquitin to, and what effect does this have? Does it require help from PI31? What proteins associate with proteasomes when sperms are being sculpted and how is this controlled by Fbxo7 and PI31. We will investigate this by comparing the ubiquitin-tagged proteins and the proteasome-associated proteins in cells from mice lacking Fbxo7 and PI31.Understanding how these events take place is important from both a pure science and a medical perspective - for example, understanding Fbxo7 function may help us understand and eventually treat sterility in some infertile patients who make no sperm. Conversely, selectively interfering with Fbxo7 function in the testes could become the basis for novel methods of male contraception. Fbxo7 is also important in other tissues: many different cell types such as red blood cells and nerve cells also undergo remodelling to transform their shapes, and Fbxo7 deficiency is also associated with anaemia and neurological conditions such as Parkinson's disease. Understanding how Fbxo7 and PI31 control cell shape in the testis may shed light on their role(s) in these other diseases as well.