In humans, structural or functional defects of the sperm flagellum induce asthenozoospermia, which accounts for the main sperm defect encountered in infertile men. Herein we focused on morphological abnormalities of the sperm flagellum (MMAF), a phenotype also termed "short tails," which constitutes one of the most severe sperm morphological defects resulting in asthenozoospermia. In previous work based on whole-exome sequencing of a cohort of 167 MMAF-affected individuals, we identified bi-allelic loss-of-function mutations in more than 30% of the tested subjects. In this study, we further analyzed this cohort and identified five individuals with homozygous truncating variants in TTC29, a gene preferentially and highly expressed in the testis, and encoding a tetratricopeptide repeat-containing protein related to the intraflagellar transport (IFT). One individual carried a frameshift variant, another one carried a homozygous stop-gain variant, and three carried the same splicing variant affecting a consensus donor site. The deleterious effect of this last variant was confirmed on the corresponding transcript and protein product. In addition, we produced and analyzed TTC29 loss-of-function models in the flagellated protist T. brucei and in M. musculus. Both models confirmed the importance of TTC29 for flagellar beating. We showed that in T. brucei the TPR structural motifs, highly conserved between the studied orthologs, are critical for TTC29 axonemal localization and flagellar beating. Overall our work demonstrates that TTC29 is a conserved axonemal protein required for flagellar structure and beating and that TTC29 mutations are a cause of male sterility due to MMAF.

中文翻译：

---

TTC29中的一种突变，编码一种进化上保守的轴突蛋白，导致弱精子症和男性不育。

在人类中，精子鞭毛的结构或功能缺陷会诱发弱精子症，这是不育男性遇到的主要精子缺陷。在这里，我们集中在精子鞭毛（MMAF）的形态异常上，这种表型也被称为“短尾巴”，它构成导致精弱无精子症的最严重的精子形态缺陷之一。在先前基于167名受MMAF影响的人群的全外显子组测序的工作中，我们在30％以上的受测受试者中发现了双等位基因功能缺失突变。在这项研究中，我们进一步分析了该队列，并确定了5个在TTC29中具有纯合的截断变异体的个体，TTC29是一个优先在睾丸中高表达的基因，并编码与鞭毛内转运（IFT）有关的含四肽重复序列的蛋白质。一个人携带一个移码变异体，另一个人携带一个纯合的终止增益变异体，三个携带相同的剪接变异体，影响共有供体位点。证实了最后一个变体对相应的转录物和蛋白质产物的有害作用。此外，我们在鞭毛的原生动物布鲁氏菌和小家鼠中产生并分析了TTC29功能丧失模型。两种模型都证实了TTC29对于鞭毛殴打的重要性。我们表明，在布鲁氏菌中，TPR结构基序在所研究的直系同源物之间高度保守，对于TTC29轴突定位和鞭毛跳动至关重要。