Functional Analysis of Two Major Sperm Tail Proteins Identifies ODF1 as Being Essential for the Tight Linkage of the Sperm Head to the Tail via SPAG4 and ODF2 as A Component of the β-catenin Destruction Complex

by Kefei Yang
Doctoral thesis
Date of Examination:2014-06-04
Date of issue:2015-04-02
Advisor:Prof. Dr. Sigrid Hoyer-Fender
Referee:Prof. Dr. Sigrid Hoyer-Fender
Referee:Prof. Dr. Dr. Wolfgang Engel
Referee:Prof. Dr. Michael Kessel
Referee:Prof. Dr. Ernst A. Wimmer
Referee:Prof. Dr. Detlef Doenecke
Referee:Prof. Dr. Martin Göpfert
Persistent Address: http://dx.doi.org/10.53846/goediss-5005

 

 

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Abstract

English

In the mammalian sperm tail, the outer dense fibers (ODFs) are accessory fibers accompanying the axonemal tubuli doublets on their outer site. The ODFs are composed of at least 14 polypeptides of which only a few have been identified. Among these components, ODF1 interacts with ODF2, and both of them are major proteins of ODFs. Although ODF1 and ODF2 have similar names, which exclusively characterize their location, the fundamental biological functions of them are entirely different. ODF1 belongs to small heat shock protein (sHSP) family, based on its overall structural features and especially on its conserved α-crystallin domain that are characteristic of sHSPs. Therefore, ODF1 was also called HSPB10. The expression of mouse Odf1 is restricted to testis and is first detectable at the round spermatid stage. In addition, immunoelectron microscopy revealed that ODF1 protein is specifically located to the ODFs and connecting piece. To study the role of ODF1 in sperm function, Odf1-deficient mice were generated and shown here that ODF1 is essential for male fertility. Homozygous ODF1-deficient male mice are infertile, whereas heterozygous male mice are fertile but show reduced sperm motility. Odf1-deficient male mice are infertile due to the detachment of the sperm head. Although headless tails are somehow motile, transmission electron microscopy revealed disturbed organization of the mitochondrial sheath, as well as of the outer dense fibers. These results thus suggest that ODF1, besides being involved in the correct arrangement of mitochondrial sheath and outer dense fibers, is essential for rigid junction of sperm head and tail. In somatic cells the cytoskeleton is linked to the nucleoskeleton by nuclear membrane proteins with conserved SUN or KASH domains. SPAG4 is a member of the SUN domain protein family and locates to the nuclear membrane. It directly interacts with ODF1 and recruits ODF1 to the nuclear membrane. Furthermore, SPAG4 is restricted to spermatids and enriched at the posterior part of elongating spermatid nuclei. However, location of SPAG4 is not affected by ODF1 deficiency. Therefore, SPAG4 and ODF1 seem to be integral components of the head-tail coupling apparatus, and the tight linkage of head to tail in sperm might be mediated by the nuclear membrane protein SPAG4 and its binding to ODF1 in the connecting piece. Whereas ODF1 is exclusively expressed in spermatids, ODF2, respectively its splice isoform Cenexin, is not only expressed in male germ cells but also localizes generally to the appendages of the mother centriole in somatic cells. As an important centrosomal component, ODF2 is essential for cilia formation and for embryonic development. Since Wnt pathway components are associated with centrosomes and vice versa centrosomal/basal body components have been implicated in modulating Wnt pathways, the relationship of ODF2 and canonical Wnt pathway was investigated. ODF2 inhibited the canonical Wnt pathway. Moreover, ODF2 over-expression repressed transcription of the endogenous Wnt target gene c-Myc and diminished XWnt8-induced secondary axis formation in Xenopus embryos. ODF2 interacted with components of the β-catenin destruction complex Axin1, Axin2, and β-catenin, and supported β-catenin degradation. Therefore, ODF2 most likely is a component of the β-catenin destruction complex, and this complex might be involved in the regulation of centrosome cohesion via promoting the degradation of β-catenin.
Keywords: connecting piece; HSPB10; HTCA; infertility; ODF1; ODF2; SPAG4; Wnt signaling pathway
 
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