Cylicins are a structural component of the sperm calyx being indispensable for male fertility in mice and human

Cylicins are testis-specific proteins, which are exclusively expressed during spermiogenesis. In mice and humans, two Cylicins, the gonosomal X-linked Cylicin 1 (Cylc1/CYLC1) and the autosomal Cylicin 2 (Cylc2/CYLC2) genes, have been identified. Cylicins are cytoskeletal proteins with an overall positive charge due to lysine-rich repeats. While Cylicins have been localized in the acrosomal region of round spermatids, they resemble a major component of the calyx within the perinuclear theca at the posterior part of mature sperm nuclei. However, the role of Cylicins during spermiogenesis has not yet been investigated. Here, we applied CRISPR/Cas9-mediated gene editing in zygotes to establish Cylc1- and Cylc2-deficient mouse lines as a model to study the function of these proteins. Cylc1 deficiency resulted in male subfertility, whereas Cylc2-/-, Cylc1-/yCylc2+/-, and Cylc1-/yCylc2-/- males were infertile. Phenotypical characterization revealed that loss of Cylicins prevents proper calyx assembly during spermiogenesis. This results in decreased epididymal sperm counts, impaired shedding of excess cytoplasm, and severe structural malformations, ultimately resulting in impaired sperm motility. Furthermore, exome sequencing identified an infertile man with a hemizygous variant in CYLC1 and a heterozygous variant in CYLC2, displaying morphological abnormalities of the sperm including the absence of the acrosome. Thus, our study highlights the relevance and importance of Cylicins for spermiogenic remodeling and male fertility in human and mouse, and provides the basis for further studies on unraveling the complex molecular interactions between perinuclear theca proteins required during spermiogenesis.

Bi-allelic variants in INSL3 and RXFP2 cause bilateral cryptorchidism and male infertility

STUDY QUESTION

What is the impact of variants in the genes INSL3 (Insulin Like 3) and RXFP2 (Relaxin Family Peptide Receptor 2), respectively, on cryptorchidism and male infertility?

SUMMARY ANSWER

Bi-allelic loss-of-function (LoF) variants in INSL3 and RXFP2 result in bilateral cryptorchidism and male infertility, whereas heterozygous variant carriers are phenotypically unaffected.

WHAT IS KNOWN ALREADY

The small heterodimeric peptide INSL3 and its G protein-coupled receptor RXFP2 play a major role in the first step of the biphasic descent of the testes, and variants in the INSL3 and RXFP2 genes have long been implicated in inherited cryptorchidism. However, only one single homozygous missense variant in RXFP2 has clearly been linked to familial bilateral cryptorchidism, so the effects of bi-allelic variants in INSL3 and heterozygous variants in both genes on cryptorchidism and male infertility remain unclear.

STUDY DESIGN, SIZE, DURATION

Exome data of 2412 men from the MERGE (Male Reproductive Genomics) study cohort including 1902 infertile men with crypto-/azoospermia, of whom 450 men had a history of cryptorchidism, were screened for high-impact variants in INSL3 and RXFP2.

PARTICIPANTS/MATERIALS, SETTING, METHODS

For patients with rare, high-impact variants in INSL3 and RXFP2, detailed clinical data were collected and the testicular phenotype was determined. Genotyping of family members was performed to analyse the co-segregation of candidate variants with the condition. Immunohistochemical staining for INSL3 in patient testicular tissue and measuring serum INSL3 concentration was performed to analyse the functional impact of a homozygous loss-of-function variant in INSL3. For a homozygous missense variant in RXFP2, its impact on the protein's cell surface expression and ability to respond to INSL3 in CRE reporter gene assay was determined.

MAIN RESULTS AND THE ROLE OF CHANCE

This study presents homozygous high-impact variants in INSL3 and RXFP2 and clearly correlates these to bilateral cryptorchidism. Functional impact of the identified INSL3 variant was demonstrated by absence of INSL3-specific staining in patients' testicular Leydig cells as well as undetectable blood serum levels. The identified missense variant in RXFP2 was demonstrated to lead to reduced RXFP2 surface expression and INSL3 mediated receptor activation.

LIMITATIONS, REASONS FOR CAUTION

Further investigations are needed to explore a potential direct impact of bi-allelic INSL3 and RXFP2 variants on spermatogenesis. With our data, we cannot determine whether the infertility observed in our patients is a direct consequence of the disruption of a possible function of these genes on spermatogenesis or whether it occurs secondarily due to cryptorchidism.

WIDER IMPLICATIONS OF THE FINDINGS

In contrast to previous assumptions, this study supports an autosomal recessive inheritance of INSL3- and RXFP2-related bilateral cryptorchidism while heterozygous LoF variants in either gene can at most be regarded as a risk factor for developing cryptorchidism. Our findings have diagnostic value for patients with familial/bilateral cryptorchidism and additionally shed light on the importance of INSL3 and RXFP2 in testicular descent and fertility.

STUDY FUNDING/COMPETING INTEREST(S)

This study was carried out within the frame of the German Research Foundation (DFG) funded by Clinical Research Unit 'Male Germ Cells: from Genes to Function' (DFG, CRU326). Research at the Florey was supported by an NHMRC grant (2001027) and the Victorian Government Operational Infrastructure Support Program. A.S.B. is funded by the DFG ('Emmy Noether Programme' project number 464240267). The authors declare no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

DDX3Y is likely the key spermatogenic factor in the AZFa region that contributes to human non-obstructive azoospermia

Non-obstructive azoospermia, the absence of sperm in the ejaculate due to disturbed spermatogenesis, represents the most severe form of male infertility. De novo microdeletions of the Y-chromosomal AZFa region are one of few well-established genetic causes for NOA and are routinely analysed in the diagnostic workup of affected men. So far, it is unclear which of the three genes located in the AZFa chromosomal region is indispensible for germ cell maturation. Here we present four different likely pathogenic loss-of-function variants in the AZFa gene DDX3Y identified by analysing exome sequencing data of more than 1,600 infertile men. Three of the patients underwent testicular sperm extraction and revealed the typical AZFa testicular Sertoli cell-only phenotype. One of the variants was proven to be de novo. Consequently, DDX3Y represents the AZFa key spermatogenic factor and screening for variants in DDX3Y should be included in the diagnostic workflow.

The piRNA-pathway factor FKBP6 is essential for spermatogenesis but dispensable for control of meiotic LINE-1 expression in humans

Infertility affects around 7% of the male population and can be due to severe spermatogenic failure (SPGF), resulting in no or very few sperm in the ejaculate. We initially identified a homozygous frameshift variant in FKBP6 in a man with extreme oligozoospermia. Subsequently, we screened a total of 2,699 men with SPGF and detected rare bi-allelic loss-of-function variants in FKBP6 in five additional persons. All six individuals had no or extremely few sperm in the ejaculate, which were not suitable for medically assisted reproduction. Evaluation of testicular tissue revealed an arrest at the stage of round spermatids. Lack of FKBP6 expression in the testis was confirmed by RT-qPCR and immunofluorescence staining. In mice, Fkbp6 is essential for spermatogenesis and has been described as being involved in piRNA biogenesis and formation of the synaptonemal complex (SC). We did not detect FKBP6 as part of the SC in normal human spermatocytes, but small RNA sequencing revealed that loss of FKBP6 severely impacted piRNA levels, supporting a role for FKBP6 in piRNA biogenesis in humans. In contrast to findings in piRNA-pathway mouse models, we did not detect an increase in LINE-1 expression in men with pathogenic FKBP6 variants. Based on our findings, FKBP6 reaches a "strong" level of evidence for being associated with male infertility according to the ClinGen criteria, making it directly applicable for clinical diagnostics. This will improve patient care by providing a causal diagnosis and will help to predict chances for successful surgical sperm retrieval.

Genetic Architecture of Azoospermia-Time to Advance the Standard of Care

BACKGROUND

Crypto- and azoospermia (very few/no sperm in the semen) are main contributors to male factor infertility. Genetic causes for spermatogenic failure (SPGF) include Klinefelter syndrome and Y-chromosomal azoospermia factor microdeletions, and CFTR mutations for obstructive azoospermia (OA). However, the majority of cases remain unexplained because monogenic causes are not analysed.

OBJECTIVE

To elucidate the monogenic contribution to azoospermia by prospective exome sequencing and strict application of recent clinical guidelines.

DESIGN, SETTING, AND PARTICIPANTS

Since January 2017, we studied crypto- and azoospermic men without chromosomal aberrations and Y-chromosomal microdeletions attending the Centre of Reproductive Medicine and Andrology, Münster.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

We performed exome sequencing in 647 men, analysed 60 genes having at least previous limited clinical validity, and strictly assessed variants according to clinical guidelines.

RESULTS AND LIMITATIONS

Overall, 55 patients (8.5%) with diagnostic genetic variants were identified. Of these patients, 20 (3.1%) carried mutations in CFTR or ADGRG2, and were diagnosed with OA. In 35 patients (5.4%) with SPGF, mutations in 20 different genes were identified. According to ClinGen criteria, 19 of the SPGF genes now reach at least moderate clinical validity. As limitations, only one transcript per gene was considered, and the list of genes is increasing rapidly so cannot be exhaustive.

CONCLUSIONS

The number of diagnostic genes in crypto-/azoospermia was almost doubled to 21 using exome-based analyses and clinical guidelines. Application of this procedure in routine diagnostics will significantly improve the diagnostic yield and clinical workup as the results indicate the success rate of testicular sperm extraction.

PATIENT SUMMARY

When no sperm are found in the semen, a man cannot conceive naturally. The causes are often unknown, but genetics play a major role. We searched for genetic variants in a large group of patients and found causal mutations for one in 12 men; these predict the chances for fatherhood.

Expression and Function of Organic Cation Transporter 2 in Pancreas

Organic cation transporters (OCT) play an important role in mediating cellular uptake of several pharmaceuticals, such as the antidiabetic drug metformin and the platinum-derived chemotherapeutics. Since these drugs can also affect the pancreas, here it was investigated whether these transporters are expressed in this organ. An interaction between OCT2 and the glucose transporter 2 (GLUT2), which is expressed with important functional consequences in the kidneys and in the pancreas, has already been demonstrated elsewhere. Therefore, here it was further investigated whether the two proteins have a functional relationship. It was demonstrated that OCT2 is expressed in pancreas, probably in β cells of Langerhans islets, together with GLUT2. However, a co-localization was only evident in a cell-line model of rat pancreatic β cells under incubation with high glucose concentration. High glucose stimulated OCT2 expression and activity. On the other side, studies conducted in human embryonic kidney cells stably expressing OCT2, showed that overexpression of GLUT2 decreased OCT2 activity. Unfortunately, pull-down experiments aimed to confirm a physical OCT2/GLUT2 interaction were not successful. Renal glucose excretion was reduced in mice with genetic deletion of OCT2. Nonetheless, in these mice no regulation of known kidney glucose transporters was measured. Therefore, it may be speculated that OCT2 may influence cellular trafficking of GLUT2, without changing its amount. OCT2 may play a role in drug uptake of the pancreas, and its activity may be regulated by glucose and GLUT2. Vice versa, GLUT2 activity may be regulated through an interaction with OCT2.