The LINC complex component Sun4 plays a crucial role in sperm head formation and fertility

Abstract

LINC complexes are evolutionarily conserved nuclear envelope bridges, physically connecting the nucleus to the peripheral cytoskeleton. They are pivotal for dynamic cellular and developmental processes, like nuclear migration, anchoring and positioning, meiotic chromosome movements and maintenance of cell polarity and nuclear shape. Active nuclear reshaping is a hallmark of mammalian sperm development and, by transducing cytoskeletal forces to the nuclear envelope, LINC complexes could be vital for sperm head formation as well. We here analyzed in detail the behavior and function of Sun4, a bona fide testis-specific LINC component. We demonstrate that Sun4 is solely expressed in spermatids and there localizes to the posterior nuclear envelope, likely interacting with Sun3/Nesprin1 LINC components. Our study revealed that Sun4 deficiency severely impacts the nucleocytoplasmic junction, leads to mislocalization of other LINC components and interferes with the formation of the microtubule manchette, which finally culminates in a globozoospermia-like phenotype. Together, our study provides direct evidence for a critical role of LINC complexes in mammalian sperm head formation and male fertility.

Formation and function of the manchette and flagellum during spermatogenesis

“…SUN4 appears to have the capacity to interact with SUN3 and Nesprin 1 and thus has been suggested to form a complex, which is required for SUN3/Nesprin 1 localization between the manchette and nucleus. In addition, the SUN1/Nesprin 3 localization appears to be wide spread in depletion of SUN4, which underlines the importance of correct formation of the SUN3/Nesprin 1 complex for precise localization of SUN1/Nesprin 3 at the posterior nuclear envelope (Pasch et al 2015). Interestingly, the SUN3/ Nesprin 1 appears to function in manchette/nucleus connection, and SUN1/Nesprin 3 may have a role in basal body attachment to the nucleus.…”

“…SUN3 and Nesprin 1 have been localized at the sites where the manchette microtubules contact the nuclear envelope (Gob et al 2010, Calvi et al 2015. Recently SUN4 has been shown to colocalize with SUN3 and Nesprin 1 (Pasch et al 2015). SUN4 appears to have the capacity to interact with SUN3 and Nesprin 1 and thus has been suggested to form a complex, which is required for SUN3/Nesprin 1 localization between the manchette and nucleus.…”

“…The importance of the manchette-nucleus connection has been further demonstrated by the testis-specific LINC component Sun4 KO (Calvi et al 2015, Pasch et al 2015. In depletion of SUN4, the manchette microtubules are not laterally associated with nuclear envelope causing round headed sperm.…”

The control of male fertility by spermatid-specific factors: searching for contraceptive targets from spermatozoon’s head to tail

“…63, 64 Sun4 -deficient mice lack the linkers between the nuclear envelope and the microtubule manchette. 65, 66 Azi1 -null spermatids show defective manchette structure and abnormal head morphologies, suggesting defects in intramanchette transport. 67 Inactivation of Spem1 in mice results in deformed spermatozoa characterized by ‘head-bent-back' abnormalities and male infertility, 68 and SPEM1 interacts with UBQLN1 69 and RANBP17 70 in the manchette of elongating spermatids.…”

Nuclear envelope dynamics during mammalian spermatogenesis: new insights on male fertility

“…In recent decades, numerous studies have demonstrated that spermatogenesis requires extensive rearrangement of the NE network, including the composition of its specific proteome and the localization of these proteins. Interestingly, the list of NE proteins restricted to or highly enriched in mammalian male germline cells is rapidly increasing, comprising a total of 10 NE components at present (Furukawa, Inagaki & Hotta, ; Schutz et al ., ; Gob et al ., ; Morimoto et al ., ; Pierre et al ., ; Pasch et al ., ; Chen et al ., ; Shang et al ., ; Elkhatib et al ., ). Furthermore, there is growing evidence that mutations in human genes encoding NE proteins can have deleterious effects on the development of fertilization‐competent spermatozoa and lead to severe infertility phenotypes in men (Zhu et al ., , ).…”