[Frontiers in Bioscience 10, 398--419, January 1, 2005]


Steven Goossens and Frans van Roy

Department for Molecular Biomedical Research, Flanders Interuniversity Institute for Biotechnology (VIB)-Ghent University, Technologiepark 927, B-9052 Ghent (Zwijnaarde), Belgium


1. Abstract
2. Introduction: junction dynamics during spermatogenesis
3. Cadherin-mediated cell-cell adhesion
4. Adherens junctions
4.1. The adherens junction dissected
4.1.1. The cadherin/catenin complex: the major functional unit of adherens junctions in epithelia
4.1.2. The nectin/afadin/ponsin complex (NAP-complex)
4.1.3. The vezatin/myosin VIIA complex
4.2. Adherens junctions in the testis: does the cadherin/catenin complex exist in the testis?
4.3. Regulation of adherens junction assembly and disassembly in the testis
4.3.1. Phosphorylation status
4.3.2. Small GTP-binding proteins
4.3.3. Other regulatory mechanisms
4.4. Wnt signaling in the testis
5. Desmosomal cell-cell adhesion
5.1. Molecular architecture of desmosomes
5.2. Desmosome-like junctions in the testis 5.3. Regulation of desmosomal cell-cell adhesion in the testis
6. Male contraception by perturbing the Sertoli-germ cell junctions
7. Conclusions and perspectives
8. Acknowledgements
9. References


During spermatogenesis, the differentiating germ cells migrate across the seminiferous epithelium while maintaining close contact with the surrounding Sertoli cells via specialized actin-based adherens junctions (ectoplasmic specializations) and intermediate filament-based anchoring junctions (desmosome-like junctions). Although this migration is essential for correct completion of spermatogenesis, the mechanisms that regulate these anchoring junctions are largely unknown, and most of our knowledge of cell-cell adhesion in testis is based on earlier studies in epithelial tissues. In most epithelia, members of the cadherin superfamily play key roles in intercellular adhesion. Cadherins are calcium-dependent cell-cell adhesion molecules mediating numerous homotypic cell-cell interactions. Until recently there has been controversy about the presence and localization of cadherins in the testis, but now there is increasing evidence that various types of cadherins are expressed in this organ, which underscores their importance in testicular functions. Here, we review the expression patterns, regulatory mechanisms and possible roles of the cadherin-mediated cell-cell adhesion in the testis, and particularly during spermatogenesis. Moreover, attention is paid to additional molecular adhesion complexes in the testis, to associated signaling pathways and to cell adhesion-related innovative ways for male contraception.