Emelyanov Alexander V, Barcenilla-Merino Daniel, Loppin Benjamin, Fyodorov Dmitry V
Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York, USA.
Laboratoire de Biologie et Modélisation de la Cellule, École Normale Supérieure de Lyon, CNRS UMR5239, Université Claude Bernard Lyon 1, Lyon, France.
J Biol Chem. 2023 Oct;299(10):105212. doi: 10.1016/j.jbc.2023.105212. Epub 2023 Sep 2.
DNA in sperm is packed with small, charged proteins termed SNBPs (sperm nuclear basic proteins), including mammalian and Drosophila protamines. During spermiogenesis, somatic-type chromatin is taken apart and replaced with sperm chromatin in a multistep process leading to an extraordinary condensation of the genome. During fertilization, the ova face a similarly challenging task of SNBP eviction and reassembly of nucleosome-based chromatin. Despite its importance for the animal life cycle, sperm chromatin metabolism, including the biochemical machinery mediating the mutual replacement of histones and SNBPs, remains poorly studied. In Drosophila, Mst77F is one of the first SNBPs loaded into the spermatid nuclei. It persists in mature spermatozoa and is essential for sperm compaction and male fertility. Here, by using in vitro biochemical assays, we identify chaperones that can mediate the eviction and loading of Mst77F on DNA, thus facilitating the interconversions of chromatin forms in the male gamete. Unlike NAP1 and TAP/p32 chaperones that disassemble Mst77F-DNA complexes, ARTEMIS and APOLLO, orthologs of mammalian importin-4 (IPO4), mediate the deposition of Mst77F on DNA or oligonucleosome templates, accompanied by the dissociation of histone-DNA complexes. In vivo, a mutation of testis-specific Apollo brings about a defect of Mst77F loading, abnormal sperm morphology, and male infertility. We identify IPO4 ortholog APOLLO as a critical component of sperm chromatin assembly apparatus in Drosophila. We discover that in addition to recognized roles in protein traffic, a nuclear transport receptor (IPO4) can function directly in chromatin remodeling as a dual, histone- and SNBP-specific, chaperone.
精子中的DNA与称为SNBPs（精子核碱性蛋白）的小的带电荷蛋白质结合，包括哺乳动物和果蝇的鱼精蛋白。在精子发生过程中，体细胞型染色质被分解，并在一个多步骤过程中被精子染色质取代，导致基因组的异常浓缩。在受精过程中，卵子面临着类似的挑战性任务，即排出SNBPs并重新组装基于核小体的染色质。尽管精子染色质代谢对动物生命周期很重要，包括介导组蛋白和SNBPs相互替代的生化机制，但仍研究不足。在果蝇中，Mst77F是最早加载到精核中的SNBPs之一。它在成熟精子中持续存在，对精子压实和雄性生育至关重要。在这里，通过使用体外生化分析，我们鉴定了可以介导Mst77F在DNA上的排出和加载的伴侣蛋白，从而促进雄配子中染色质形式的相互转化。与拆解Mst77F-DNA复合物的NAP1和TAP/p32伴侣蛋白不同，ARTEMIS和APOLLO是哺乳动物输入蛋白-4（IPO4）的直系同源物，它们介导Mst77F在DNA或寡核小体模板上的沉积，同时伴随着组蛋白-DNA复合物的解离。在体内，睾丸特异性Apollo的突变导致Mst77F加载缺陷、精子形态异常和雄性不育。我们鉴定出IPO4直系同源物APOLLO是果蝇精子染色质组装装置的关键组成部分。我们发现，除了在蛋白质运输中的公认作用外，一种核转运受体（IPO4）可以作为一种双重的、组蛋白和SNBP特异性的伴侣蛋白直接在染色质重塑中发挥作用。
