Ectoplasmic specialization: A friend or a foe of spermatogenesis?

The ectoplasmic specialization (ES) is a testis-specific, actin-based hybrid anchoring and tight junction. It is confined to the interface between Sertoli cells at the blood-testis barrier, known as the basal ES, as well as between Sertoli cells and developing spermatids designated the apical ES. The ES shares features of adherens junctions, tight junctions and focal contacts. By adopting the best features of each junction type, this hybrid nature of ES facilitates the extensive junction-restructuring events in the seminiferous epithelium during spermatogenesis. For instance, the α6β1-integrin- laminin 333 complex, which is usually limited to the cell-matrix interface in other epithelia to facilitate cell movement, is a putative apical ES constituent. Furthermore, JAM-C and CAR, two tight junction integral membrane proteins, are also components of apical ES involving in spermatid orientation. We discuss herein the mechanisms that maintain the cross-talk between ES and blood-testis barrier to facilitate cell movement and orientation in the seminiferous epithelium. © 2006 Wiley Periodicals, Inc.postprin

Ectoplasmic specialization: A friend or a foe of spermatogenesis?

The ectoplasmic specialization (ES) is a testis-specific, actin-based hybrid anchoring and tight junction. It is confined to the interface between Sertoli cells at the blood-testis barrier, known as the basal ES, as well as between Sertoli cells and developing spermatids designated the apical ES. The ES shares features of adherens junctions, tight junctions and focal contacts. By adopting the best features of each junction type, this hybrid nature of ES facilitates the extensive junction-restructuring events in the seminiferous epithelium during spermatogenesis. For instance, the α6β1-integrin- laminin 333 complex, which is usually limited to the cell-matrix interface in other epithelia to facilitate cell movement, is a putative apical ES constituent. Furthermore, JAM-C and CAR, two tight junction integral membrane proteins, are also components of apical ES involving in spermatid orientation. We discuss herein the mechanisms that maintain the cross-talk between ES and blood-testis barrier to facilitate cell movement and orientation in the seminiferous epithelium. © 2006 Wiley Periodicals, Inc.postprin

Dynamic II interacts with the cadherin- and occludin-based protein complexes at the blood-testis barrier in adult rat testes

In adult rat testes, blood-testis barrier (BTB) restructuring facilitates the migration of preleptotene spermatocytes from the basal to the adluminal compartment that occurs at stage VIII of the epithelial cycle. Structural proteins at the BTB must utilize an efficient mechanism (e.g. endocytosis) to facilitate its transient 'opening'. Dynamin II, a large GTPase known to be involved in endocytosis, was shown to be a product of Sertoli and germ cells in the testis. It was also localized to the BTB, as well as the apical ectoplasmic specialization (apical ES), during virtually all stages of the epithelial cycle. By co-immunoprecipitation, dynamin II was shown to associate with occludin, N-cadherin, zonula occludens-1 (ZO-1), β-catenin, junctional adhesion molecule-A, and p130Cas, but not nectin-3. An in vivo model in rats previously characterized for studying adherens junction (AJ) dynamics in the testes by adjudin (formerly called AF-2364, 1-(2,4-dichlorobenzyl)-1H-indazole-3-carhohydrizide) treatment was used in our studies. At the time of germ cell loss from the seminiferous epithelium as a result of adjudin-induced AJ restructuring without disrupting the BTB integrity, a significant decline in the steady-state dynamin II protein level was detected. This change was associated with a concomitant increase in the levels of two protein complexes at the BTB, namely occludin/ZO-1 and N-cadherin/ β-catenin. Interestingly, these changes were also accompanied by a significant increase in the structural interaction of dynamin II with β-catenin and ZO-1. β-Catenin and ZO-1 are adaptors that structurally link the cadherin- and occludin-based protein complexes together at the BTB in an 'engaged'state to reinforce the barrier function in normal testes. However, β-catenin and ZO-1 were 'disengaged' from each other but bound to dynamin II during adjudin-induced AJ restructuring in the testis. The data reported herein suggest that dynamin II may assist the 'disengagement' of β-catenin from ZO-1 during BTB restructuring. Thus, this may permit the occludin /ZO-1 complexes to maintain the BTB integrity when the cadherin/catenin complexes are dissociated to facilitate germ cell movement. © 2006 Society for Endocrinology.link_to_subscribed_fulltex

Frequent Inactivation of Axon Guidance Molecule RGMA in Human Colon Cancer Through Genetic and Epigenetic Mechanisms

Background & Aims: Repulsive guidance molecule member A (RGMA) is a glycosylphosphatidylinositol-anchored glycoprotein and axon guidance molecule that signals through its receptor, neogenin (NEO1), a homologue of the deleted-in-colorectal cancer (DCC) gene. RGMA also functions as a bone morphogenetic protein (BMP) coreceptor. We studied the potential roles of RGMA and NEO1 in colorectal cancer (CRC) pathogenesis. Methods: We analyzed expression of RGMA and NEO1, as well as their epigenetic and genetic changes, in a large series of CRC samples, normal colon tissues, adenomas, and cell lines. These studies were accompanied by in vitro functional assay. Results: RGMA and NEO1 expression were significantly down-regulated in most CRCs, adenomas, and cell lines. RGMA was frequently silenced by promoter methylation in CRCs (86.7%), adenomas (90.9%), and CRC cell lines (92.3%) but not in normal colon tissues; allelic imbalance of RGMA and NEO1 was observed in 40% and 49% of CRCs, respectively. In CRC samples, reduced RGMA levels were significantly associated with mismatch repair deficiency or mutations in KRAS or BRAF. Exposure to 5-aza-2′-deoxycytidine restored RGMA expression in CRC cell lines. Transfection of RGMA into CRC cells suppressed cell proliferation, migration, and invasion and also increased apoptosis in response to DNA-damaging agent. Conclusions: The frequent genetic and epigenetic inactivation of RGMA in CRCs and adenomas along with its in vitro function collectively support its role as a tumor suppressor in colon cells. These findings add to the expanding list of axon guidance molecules with disrupted function during colon carcinogenesis and create new opportunities for early detection and drug development. © 2009 AGA Institute.link_to_subscribed_fulltex

A peptide derived from laminin-γ3 reversibly impairs spermatogenesis in rats

Cellular events that occur across the seminiferous epithelium of the mammalian testis during spermatogenesis are tightly coordinated by biologically active peptides released from laminin chains. Laminin-γ3 domain IV (Lam γ3 DIV) is released at the apical ectoplasmic specialization (ES) during spermiation and mediates restructuring of the blood-testis barrier (BTB), which facilitates the transit of preleptotene spermatocytes. Here we determine the biologically active domain in Lam γ3 DIV, which we designate F5-peptide, and show that overexpression of this domain, or the use of a synthetic F5-peptide, in Sertoli cells with an established functional BTB reversibly perturbs BTB integrity in vitro and in rat testis in vivo. This effect is mediated via changes in protein distribution at the Sertoli and Sertoli-germ cell-cell interface and by phosphorylation of focal adhesion kinase at Tyr(407). The consequences are perturbed organization of actin filaments in Sertoli cells, disruption of the BTB and spermatid loss. The impairment of spermatogenesis suggests that this laminin peptide fragment may serve as a contraceptive in male rats