4 DISCUSSION
Sex chromosomes play a key factor in sex determination and reproductive
function (Skaletsky et al., 2003). Other than genes located in the
autosomal chromosome, sex chromosome genes lack corresponding alleles.
Therefore, harmful mutations in sex chromosome genes have a direct
impact on male infertility occurrence. To date, limited genetic causes
in sex chromosomes have been acknowledged. For example, azoospermia
factor (AZF), located on the long arm of the Y chromosome, is composed
of AZFa, AZFb, and AZFc (Muller et al., 2008). Previous studies have
revealed that AZF microdeletion is related to NOA and severe
oligospermia (Yoshida et al., 2014; Navarro-Costa et al., 2010; Colaco
et al., 2018). Deleted in azoospermia 1 (DAZ1 ),ubiquitin-specific peptidase 9 Y-linked (USP9Y), and RNA
binding motif protein Y-linked family 1 member A1 (RBMY) in the AZF
region are identified as candidate causative genes in spermatogenesis.
Similar to the Y chromosome, the X chromosome contains genes with
exclusive or predominant expression in the testis. Partial deletion oftestis expressed 11 (TEX11) leads to azoospermia due to meiotic
arrest; mutations in androgen receptor (AR) attenuate AR
regulation of target gene expression and cause oligozoospermia and
azoospermia; dysfunction of adhesion G protein-coupled receptor G2
(ADGRG2) results in a buildup of fluid within the testis and an
accumulation of spermatozoa within the efferent ducts; Dynein
axonemal assembly factor 6 (DAAF6 ) is involved in the assembly
of the dynein arm of the ciliary axoneme, and defects in this gene lead
to primary ciliary dyskinesia (PCD). Hence, more sex chromosome gene
pathogenicity and biological functions in male reproduction need to be
explored.
A previous study on an animal model reported a necessary role ofCfap47 in spermatogenesis in mice, and their patients were
infertile, characterized by abnormal sperm motility and morphology.
However, the phenotype and genotype of CFAP47 in humans have not
been comprehensively studied, and the underlying mechanism by whichCFAP47 regulates reproductive biology is limited. In the present
study, we detected a novel recurrent missense mutation of CFAP47,which is located in the X chromosome, in two sterile patients from two
unrelated families. Further in vitro experiments confirmed the
pathogenicity of this mutation. By a comprehensive morphology analysis,
we first suggested that CFAP47 mutation is linked to abnormal
annulus and aberrations in sperm morphology either in the head or
flagellum. More importantly, we explored the interacting proteins of
CFAP47 and investigate the molecular mechanism of CFAP47 in sperm
morphology. Interestingly, CFAP69 and CFAP65, known MMAF pathogenic
genes, are required for flagella assembly and stability in sperm cells.
Wang et al. reported that CFAP65 is expressed in the acrosome area and
flagellar midpiece in normal human spermatozoa, and CFAP69 is localized
to the sperm flagellum. We thus speculated that CFAP47 may be involved
in spermatogenesis by interacting with CFAP65 and CFAP69. Moreover,
damaged expression of CFAP65 and CFAP69 was detected in the sperm of the
patients. Additionally, the co-expression of CFAP47 with CFAP65 and
CFAP69 in various spermatogenic spermatids in the testes of humans and
mice during spermatogenesis has been presented. These findings indicate
a potential role of CFAP47 in regulating spermatogenesis through
interacting with CFAP65 and CFAP69. Our study expands the mutational and
phenotypic spectrum of CFAP47 and strongly elucidates the
important role of CFAP47 in male reproduction.
In summary, our study identified a novel missense mutation inCFAP47 in two infertile male patients with various sperm
morphology abnormalities. Our work presented more detailed information
on the pathogenesis of CFAP47 -mutated MMAF and provided direct
evidence that suggests the involvement of CFAP47 in
spermatogenesis.