Ultra-structure of the sperm head-to-tail linkage complex in the absence of the spermatid-specific LINC component SPAG4

Abstract

Tight connection between sperm head and tail is crucial for the transport of the male genome and fertilization. The linkage complex, the sperm head-to-tail coupling apparatus (HTCA), originates from the centrosome and anchors to the nuclear membrane. In contrast to its ultra-structural organization, which is already well known for decades, its protein composition largely still awaits future deciphering. SUN-domain proteins are essential components of a complex that links the cytoskeleton to the peripheral nucleoskeleton, which is the nuclear lamina. Here, we studied the impact of the SUN protein SPAG4/SUN4 on the formation of the HTCA. SPAG4/SUN4 is specifically expressed in haploid male germ cells showing a polarized distribution towards the posterior pole in late spermatids that corresponds to the tail attachment site. SPAG4-deficient male mice are infertile with compromised manchette formation and malformed sperm heads. Nonetheless, sperm tails are present demonstrating dispensability of a proper manchette for their formation. Ultra-structural analyses revealed that the development of the sperm head-to-tail linkage complex in the absence of SPAG4 resembles that in the wild type. However, in SPAG4-deficient sperm, the attachment site is diminished with obvious lateral detachment of the HTCA from the nucleus. Our results thus indicate that SPAG4, albeit not essential for the formation of the HTCA per se, is, nevertheless, required for tightening the sperm head-to-tail anchorage by provoking the correct attachment of the lateral parts of the basal plate to the implantation fossa.

Sperm quality parameters are increased and asymmetric in house mouse hybrids

“…Linking of ODF1 to microtubules might occur via ODF1/SPAG5 [chromosome 11] / SPAG4 [chromosome 2] interaction. SPAG4 knock-out mice demonstrate that the SPAG4 itself is not essential for the formation of the sperm head-to-tail coupling apparatus, nevertheless, SPAG4 is required for tightening the sperm head-to-tail anchorage (Yang et al 2018). Surprisingly, none of the genes noted above are located on the sex chromosomes, and only two autosomal genes ( Odf1 and Ppp1r16a) lie within the intervals identified for QTLs of DSH (White et al, 2011).…”

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

“…In mice, this testis‐specific protein is localized at the posterior nuclear pole of round and elongating spermatids, where it concentrates specifically at lateral NE regions that contact with manchette‐associated microtubules (Table ; Fig. ) (Calvi et al ., ; Pasch et al ., ; Yang et al ., ). Importantly, SUN4 co‐localizes completely with both SUN3 and nesprin‐1 along the posterior side of the NE excluding the implantation fossa of mouse spermatids, which is suggestive that the three proteins may work together at the manchette–NE intersection (Table ; Fig.…”

“…Of note, the interaction of SUN4 with SUN3 may contribute to the retention of the latter at the NE of spermatids, given that the short N‐terminal domain of SUN3 is predicted not to provide sufficient stability for its immobilization in the INM (Calvi et al ., ). Furthermore, the deletion of Sun4 in mice severely impairs manchette development, wherein the associated microtubule bundles fail to assemble laterally on the nuclear periphery and are highly disorganized or partially missing (Calvi et al ., ; Pasch et al ., ; Yang et al ., ), accompanied by an abnormal expansion of the acrosomal vesicle across almost the entire NE surface of elongating spermatids (Table ; Fig. ) (Calvi et al ., ).…”

“…Relevant NE proteins include: four nuclear lamina proteins, namely lamins A/C, B1, B3 and C2; 10 INM proteins, specifically Dpy‐19‐like protein 2 (DPY19L2), lamina‐associated polypeptides 1 and 2 (LAP1 and LAP2), lamin B receptor (LBR), LAP2/emerin/MAN1 (LEM) domain‐containing protein 1 (LEMD1) and Sad‐1/UNC‐84 homology domain‐containing proteins 1–5 (SUN1–SUN5, among which is the SUN1η isoform); three ONM proteins, including Klarsicht/ANC‐1/Syne‐1 homology domain‐containing protein 5 (KASH5), nesprin‐1 and nesprin‐3; and a newly identified NE protein termed spermatogenesis‐associated 46 (SPATA46). Of note, the expression of lamin B3 (Furukawa & Hotta, ; Schutz et al ., ), lamin C2 (Furukawa et al ., ), DPY19L2 (Carson, Cheung & Scherer, ; Pierre et al ., ), LEMD1 (Yuki et al ., ; Elkhatib et al ., ), SUN1η, SUN3 (Gob et al, ), SUN4 (Shao et al ., ; Pasch et al ., ; Yang et al, ), SUN5 (Frohnert, Schweizer & Hoyer‐Fender, ; Jiang et al ., ; Shang et al ., ), KASH5 (Morimoto et al ., ; Horn et al ., ) and SPATA46 (Chen et al ., ) is largely restricted to male germline cells, suggesting highly specialized roles in the testis.…”

“…Similar to the SUN proteins discussed above, SUN4 has been described to be exclusively expressed during mouse (Calvi et al ., ; Pasch et al ., ; Yang et al ., ), rat (Shao et al ., ) and human (Yeh et al ., ) spermiogenesis, exhibiting a close association with microtubule‐based structures (Table ; Fig. ).…”