Background Mutation in S-phase cyclin A-associated protein rin the endoplasmic reticulum (SCAPER) have been found across ethnicities and have been shown to cause variable penetrance of an array of pathological traits, including intellectual disability, retinitis pigmentosa and ciliopathies.
Methods Human clinical phenotyping, surgical testicular sperm extraction and testicular tissue staining. Generation and analysis of short spindle 3 (ssp3) (SCAPER orthologue) Drosophila CAS9-knockout lines. In vitro microtubule (MT) binding assayed by total internal reflection fluorescence microscopy.
Results We show that patients homozygous for a SCAPER mutation lack SCAPER expression in spermatogonia (SPG) and are azoospermic due to early defects in spermatogenesis, leading to the complete absence of meiotic cells. Interestingly, Drosophila null mutants for the ubiquitously expressed ssp3 gene are viable and female fertile but male sterile. We further show that male sterility in ssp3 null mutants is due to failure in both chromosome segregation and cytokinesis. In cells undergoing male meiosis, the MTs emanating from the centrosomes do not appear to interact properly with the chromosomes, which remain dispersed within dividing spermatocytes (SPCs). In addition, mutant SPCs are unable to assemble a normal central spindle and undergo cytokinesis. Consistent with these results, an in vitro assay demonstrated that both SCAPER and Ssp3 directly bind MTs.
Conclusions Our results show that SCAPER null mutations block the entry into meiosis of SPG, causing azoospermia. Null mutations in ssp3 specifically disrupt MT dynamics during male meiosis, leading to sterility. Moreover, both SCAPER and Ssp3 bind MTs in vitro. These results raise the intriguing possibility of a common feature between human and Drosophila meiosis.
- reproductive medicine
- clinical genetics
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OW and YL are joint first authors.
EL, OSB and UA are joint senior authors.
OW and YL contributed equally.
EL, OSB and UA contributed equally.
Correction notice The article has been corrected since it was published Online First. The name of author Ali AbuMadighem has been corrected.
Contributors UA initiated the study. UA, OSB, YL, MH and OW contributed to its conception and design, and together with EL, SB, MG and LG drafted the manuscript. OW, YL, AB, SB, LG, MG, MH, AAM, RJM, KO, SER, IH-V, EL, OSB and UA acquired and analysed data. EL, IH-V, SEL and OSB provided the clinical data.
Funding These studies were funded in part by the Morris Kahn Foundation and supported through the National Knowledge Center for Rare/Orphan Diseases sponsored by the Israeli Ministry of Science, Technology and Space (to OSB), and by Associazione Italiana per la Ricerca sul Cancro (IG grant 20 528 to MG). RJM is supported by grant R35GM124889 from the NIH.
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval This study was done following Soroka Medical Center institutional review board approval (#5071G and #4538) with informed consent of studied individuals or their legal guardians.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available upon reasonable request.
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