IQUB deficiency causes male infertility by affecting the activity of p-ERK1/2/RSPH3

Can new genetic factors responsible for male infertility be identified, especially for those characterized by asthenospermia despite normal sperm morphology?

We identified the novel pathogenetic gene IQ motif and ubiquitin-like domain-containing (IQUB) as responsible for male infertility characterized by asthenospermia, involving sperm radial spoke defects.

To date, only a few genes have been found to be responsible for asthenospermia with normal sperm morphology. Iqub, encoding the IQUB protein, is highly and specifically expressed in murine testes and interacts with the proteins radial spoke head 3 (RSPH3), CEP295 N-terminal like (CEP295NL or DDC8), glutathione S-transferase mu 1 (GSTM1) and outer dense fiber of sperm tails 1 (ODF1) in the yeast two-hybrid system.

The IQUB variant was identified by whole-exome sequencing in a cohort of 126 male infertility patients with typical asthenospermia recruited between 2015 and 2020. Knockout (KO) and knockin (KI) mouse models, scanning and transmission electron microscopy (TEM), and other functional assays were performed, between 2019 and 2021.

The IQUB variant was identified by whole-exome sequencing and confirmed by Sanger sequencing. Iqub KO and KI mice were constructed to mimic the phenotype of the affected individual. After recapitulating the phenotype of human male infertility, scanning and TEM were performed to check the ultrastructure of the sperm. Western blot and co-immunoprecipitation were performed to clarify the pathological mechanism of the IQUB variant.

We identified a homozygous nonsense IQUB variant (NM_001282855.2:c.942T> G(p.Tyr314*)) from an infertile male. Iqub KO and KI mice mimicked the infertility phenotype and confirmed IQUB to be the pathogenetic gene. Scanning and TEM showed that sperm of both the mouse models and the affected individual had radial spoke defects. The functional assay suggested that IQUB may recruit calmodulin in lower Ca2+ environments to facilitate the normal assembly of radial spokes by inhibiting the activity of RSPH3/p-ERK1/2 (a nontypical AKAP (A-Kinase Anchoring Protein) forming by RSPH3 and phosphorylation of extracellular signal-regulated kinase 1 and 2 (p-ERK1/2)).

Additional cases are needed to confirm the genetic contribution of IQUB variants to male infertility. In addition, because no IQUB antibody is available for immunofluorescence and the polyclonal antibody we generated was only effective in western blotting, immunostaining for IQUB was not performed in this study. Therefore, this study lacks direct in vivo proof to confirm the effect of the variant on IQUB protein level.

Our results suggest a causal relation between IQUB variants and male infertility owing to asthenospermia, and partly clarify the pathological mechanism of IQUB variants. This expands our knowledge of the genes involved in human sperm asthenospermia and potentially provides a new genetic marker for male infertility.

This work was supported by the National Key Research and Development Program of China (2021YFC2700100), the National Natural Science Foundation of China (32130029, 82171643, 81971450, 82001538, and 81971382) and the Guangdong Science and Technology Department Guangdong-Hong Kong-Macao Joint Innovation Project (2020A0505140003). There are no competing interests to declare.

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