Ultra-structure of the sperm head-to-tail linkage complex in the absence of the spermatid-specific LINC component SPAG4
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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.
KeywordsHTCA LINC SUN domain Male fertility
We gratefully acknowledge the kind gift of RNA probes from cultured SSC and ES cells by Jessica Nolte (Göttingen). We would also thank Gerd Kripp for the technical assistance.
KY performed the experiments; IMA was responsible for generation of knock out animals; AM was responsible for the ultra-structural investigations and contributed to manuscript main text; SH-F designed the experiments, wrote the main manuscript text, and prepared the figures.
Compliance with ethical standards
Conflict of interest
I declare that there is no conflict of interest that could perceived as prejudicing the impartiality of the research reported.
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