P-720 Biallelic variants in IQCN cause sperm flagella assembly defects and male infertility
Authors: Dai J , Qi L , Fei G , Guangxiu L , Ge L 
Published: June 2023

Abstract

Study question
What is the effect of defects in the manchette protein IQ motif-containing N (IQCN) on sperm flagellar assembly?

Summary answer
Deficiency in IQCN is responsible for sperm flagella assembly defects and abnormal computer-assisted sperm analysis (CASA) parameters, which result in male infertility.

What is known already
Manchette is a transient structure that is involved in the shaping of the spermatid nucleus and protein transport of flagella. Most recently, our group reported that the manchette protein IQCN is essential for fertilization. Variants in IQCN led to total fertilization failure (TFF) and defective acrosome structure phenotypes. However, the related function of IQCN in sperm flagella assembly is still unknown.

Study design, size, duration
Fifty infertile males were recruited from the Reproductive and Genetic Hospital of China International Trust Investment Corporation (CITIC)-Xiangya from January 2014 to October 2022.

Participants/materials, setting, methods
Genomic DNA was extracted from the peripheral blood samples of the affected individuals for whole-exome sequencing. The ultrastructure of the flagella was detected by transmission electron microscopy (TEM). CASA was used to test the parameters of sperm motility. An Iqcn knockout (Iqcn-/-) mouse model was generated by CRISPER-Cas9 technology. Immunoprecipitation (IP) followed by liquid chromatography‒mass spectrometry was used to select the differentially expressed IQCN-binding proteins. Immunofluorescence was used to validate the localization of IQCN-binding proteins.

Main results and the role of chance
Biallelic variants in IQCN (c.3913A&gt;T and c.3040A&gt;G; c.2453_2454del) were identified in our infertile cohort. The sperm from the affected individuals showed irregular “9 + 2” structure of sperm flagella, which resulted in abnormal CASA parameters. Similar phenotypes were observed in Iqcn-/- male mice. The CASA parameters in the sperm of Iqcn-/- male mice were significantly lower than those in Iqcn+/+ male mice. The partial of peripheral doublet microtubules (DMTs) and outer dense fibers (ODFs) were absent, or the chaotic arrangement of DMTs were observed in the principal piece and end piece of sperm flagella. The hyperactivation ability of sperm from Iqcn-/- male mice was decreased than sperm from Iqcn+/+ male mice. The CDC42 and IFT protein families are hub proteins that interact with IQCN and regulate flagella assembly during spermiogenesis. Deficiency in IQCN causes the loss of binding with CDC42 and IFT74, which leads to the absence or abnormal localization of CDC42 and IFT74 in mouse and human spermatozoa.

Limitations, reasons for caution
More cases are needed to demonstrate the relationship between the IQCN variations and the phenotypes.

Wider implications of the findings
Our findings expand the genetic and phenotypic spectrum of IQCN variants in causing male infertility, thus providing a genetic marker for sperm motility deficiency and male infertility.

Trial registration number
N.A.