Mammalian Sperm Head Formation Involves Different Polarization of Two Novel LINC Complexes

Abstract

BackgroundLINC complexes are nuclear envelope bridging protein structures formed by interaction of SUN and KASH proteins. They physically connect the nucleus with the peripheral cytoskeleton and are critically involved in a variety of dynamic processes, such as nuclear anchorage, movement and positioning and meiotic chromosome dynamics. Moreover, they are shown to be essential for maintaining nuclear shape.FindingsBased on detailed expression analysis and biochemical approaches, we show here that during mouse sperm development, a terminal cell differentiation process characterized by profound morphogenic restructuring, two novel distinctive LINC complexes are established. They consist either of spermiogenesis-specific Sun3 and Nesprin1 or Sun1η, a novel non-nuclear Sun1 isoform, and Nesprin3. We could find that these two LINC complexes specifically polarize to opposite spermatid poles likely linking to sperm-specific cytoskeletal structures. Although, as shown in co-transfection/immunoprecipitation experiments, SUN proteins appear to arbitrarily interact with various KASH partners, our study demonstrates that they actually are able to confine their binding to form distinct LINC complexes.ConclusionsFormation of the mammalian sperm head involves assembly and different polarization of two novel spermiogenesis-specific LINC complexes. Together, our findings suggest that theses LINC complexes connect the differentiating spermatid nucleus to surrounding cytoskeletal structures to enable its well-directed shaping and elongation, which in turn is a critical parameter for male fertility.

Formation and function of the manchette and flagellum during spermatogenesis

“…The manchette appears to be connected to the nucleoskeleton through the linker of nucleoskeleton and cytoskeleton (LINC) complex (Gob et al 2010). In somatic cells, the LINC complex (Luxton & Starr 2014).…”

“…KASH proteins interact with SUN proteins located in inner nuclear membrane, and this bridge is essential for coupling nuclear structure to cytoskeleton (Crisp et al 2006). Two LINC complexes have been implicated during spermatid elongation; SUN3/Nesprin 1 complex connects the manchette to the nucleus, and SUN1/Nesprin 3 shows an atypical non-nuclear localization at the anterior pole (Gob et al 2010). 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.…”

“…Two LINC complexes have been implicated during spermatid elongation; SUN3/Nesprin 1 complex connects the manchette to the nucleus, and SUN1/Nesprin 3 shows an atypical non-nuclear localization at the anterior pole (Gob et al 2010). 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).…”

SUN1 splice variants, SUN1_888, SUN1_785, and predominant SUN1_916, variably function in directional cell migration

“…[5][6][7][8][9] LINC complexes and nuclear lamins form a solid scaffold for diverse functions including nuclear migration, 10 nuclear shaping and positioning,. 11,12 maintaining the centrosome-nucleus connection, 13,14 mechanotransduction, 15,16 DNA repair, 17,18 nuclear membrane spacing, cancer, and recessive cerebellar ataxia.…”

Cytoskeletal track selection during cargo transport in spermatids is relevant to male fertility

“…3 A spermiogenesis-specific LINC complex (for linker of nucleoskeleton and cytoskeleton) bridges the dense nuclear lamina to F-actin in the acroplaxome. 7 As a result, the acroplaxome not only stabilizes the acrosome during the acrosome-acroplaxome complex and the regulatory dynamics of F-actin in the acroplaxome, including the expression of cortactin transcripts in spermatids. We highlight the consistent acroplaxome-to-manchette-to HTCA sequential redistribution of several proteins and add two proteins to an enlarging catalog: Hook1, a protein that binds vesicle cargos to microtubules, and dynactin (p150Glued), a member of a protein complex that associates with of cytoplasmic dynein during the transport of vesicle cargos along microtubules.…”