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Ezrin: a regulator of actin microfilaments in cell junctions of the rat testis.

Gungor-Ordueri NE, Celik-Ozenci C, Cheng CY - Asian J. Androl. (2015 Jul-Aug)

Bottom Line: Thus, these proteins are crucial to confer integrity of the apical membrane domain and its associated junctional complex, namely the tight junction and the adherens junction.Since ectoplasmic specialization (ES) is an F-actin-rich testis-specific anchoring junction-a highly dynamic ultrastructure in the seminiferous epithelium due to continuous transport of germ cells, in particular spermatids, across the epithelium during the epithelial cycle-it is conceivable that ERM proteins are playing an active role in these events.Although these proteins were first reported almost 25 years and have since been extensively studied in multiple epithelia/endothelia, few reports are found in the literature to examine their role in the actin filament bundles at the ES.

View Article: PubMed Central - PubMed

Affiliation: The Mary M. Wohlford Laboratory for Male Contraceptive Research, Center for Biomedical Research, Population Council, New York, USA.

ABSTRACT
Ezrin, radixin, moesin and merlin (ERM) proteins are highly homologous actin-binding proteins that share extensive sequence similarity with each other. These proteins tether integral membrane proteins and their cytoplasmic peripheral proteins (e.g., adaptors, nonreceptor protein kinases and phosphatases) to the microfilaments of actin-based cytoskeleton. Thus, these proteins are crucial to confer integrity of the apical membrane domain and its associated junctional complex, namely the tight junction and the adherens junction. Since ectoplasmic specialization (ES) is an F-actin-rich testis-specific anchoring junction-a highly dynamic ultrastructure in the seminiferous epithelium due to continuous transport of germ cells, in particular spermatids, across the epithelium during the epithelial cycle-it is conceivable that ERM proteins are playing an active role in these events. Although these proteins were first reported almost 25 years and have since been extensively studied in multiple epithelia/endothelia, few reports are found in the literature to examine their role in the actin filament bundles at the ES. Studies have shown that ezrin is also a constituent protein of the actin-based tunneling nanotubes (TNT) also known as intercellular bridges, which are transient cytoplasmic tubular ultrastructures that transport signals, molecules and even organelles between adjacent and distant cells in an epithelium to coordinate cell events that occur across an epithelium. Herein, we critically evaluate recent data on ERM in light of recent findings in the field in particular ezrin regarding its role in actin dynamics at the ES in the testis, illustrating additional studies are warranted to examine its physiological significance in spermatogenesis.

No MeSH data available.


Related in: MedlinePlus

A schematic drawing illustrating the likely role of ezrin in the apical ectoplasmic specialization (ES) during the epithelial cycle in the rat testis. Ezrin is an actin-binding protein at the ES but restrictively expressed at the apical ES at stage VIII of the epithelial cycle, which is robustly expressed at early VIII and begins to diminish by late VIII,27 as depicted herein. At early stage VIII (left panel), ezrin likely recruits actin regulatory proteins to the apical ES, such as actin-related protein 3 (Arp3) to initiate actin microfilament re-organization, such as by converting bundled microfilaments to an unbundled and branched network to facilitate endocytic vesicle-mediated protein trafficing, such as endocytosis, transcytosis and recycling, which in turn facilitates the assembly of new apical when step 8 spermatids arise at this stage. At late stage VIII (right panel), the expression of ezrin diminishes considerably,27 and a knockdown of ezrin has shown that a transient loss of ezrin in Sertoli cells leads to actin microfilament truncation and defragmentation, likely the result of Arp2/3-mediated actin re-organization, coupled with a mis-localization of actin bundling protein palladin.27 This thus further potentiates apical ES restructuring, facilitating the release of sperms at spermiation. Furthermore, MMP2-mediated degration of laminin chains generate biologically active peptide fragments to induce blood-testis barrier (BTB) restructuring,5758 coordinating the events of spermation and BTB remodeling at stage VIII of the cycle. It is noted that this is a hypothetical model, and much research is needed to confirm this concept. However, it serves as a working model for future investigations as discussed in text.
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Figure 3: A schematic drawing illustrating the likely role of ezrin in the apical ectoplasmic specialization (ES) during the epithelial cycle in the rat testis. Ezrin is an actin-binding protein at the ES but restrictively expressed at the apical ES at stage VIII of the epithelial cycle, which is robustly expressed at early VIII and begins to diminish by late VIII,27 as depicted herein. At early stage VIII (left panel), ezrin likely recruits actin regulatory proteins to the apical ES, such as actin-related protein 3 (Arp3) to initiate actin microfilament re-organization, such as by converting bundled microfilaments to an unbundled and branched network to facilitate endocytic vesicle-mediated protein trafficing, such as endocytosis, transcytosis and recycling, which in turn facilitates the assembly of new apical when step 8 spermatids arise at this stage. At late stage VIII (right panel), the expression of ezrin diminishes considerably,27 and a knockdown of ezrin has shown that a transient loss of ezrin in Sertoli cells leads to actin microfilament truncation and defragmentation, likely the result of Arp2/3-mediated actin re-organization, coupled with a mis-localization of actin bundling protein palladin.27 This thus further potentiates apical ES restructuring, facilitating the release of sperms at spermiation. Furthermore, MMP2-mediated degration of laminin chains generate biologically active peptide fragments to induce blood-testis barrier (BTB) restructuring,5758 coordinating the events of spermation and BTB remodeling at stage VIII of the cycle. It is noted that this is a hypothetical model, and much research is needed to confirm this concept. However, it serves as a working model for future investigations as discussed in text.

Mentions: Ezrin was first reported in the mouse testis by fluorescence microscopy, illustrating it is expressed by Sertoli and germ cells, associated with actin microfilaments, involved in spermiogenesis and the maturation of Sertoli cells.26 Besides expressed predominantly at the Sertoli cell-step 16 spermatid interface in the mouse testis during the epithelial cycle, ezrin is notably expressed in the ultrastructure of residual bodies at stage VIII of the epithelial cycle.26 In humans, ezrin was found to be associated with spermatozoa, involving in sperm capacitation, possibly due to its role in maintaining the actin-based cytoskeleton and the associated proteins necessary to confer capacitation.28 A recent study has shown that ezrin is indeed an actin-binding protein in the rat testis,27 consistent with an earlier report by immunoprecipitation, illustrating ezrin binds to actin microfilaments in the mouse testis.26 Besides interacting with actin in Sertoli cells (Figure 2), ezrin also binds to Arp3 (which together Arp2 forms the Arp2/3 complex, and when it is activated by neuronal Wiskott–Aldrich Syndrome protein (N-WASP), the Arp2/3-N-WASP complex is known to induce barbed end nucleation, causing branched actin polymerization,4950 effectively converting actin microfilaments from a “bundled” to an “unbundled/branched” configuration), JAM-A, N-cadherin, c-Src and p-FAK-Tyr397.27 These findings are important since they illustrate the possibility that ezrin, besides an actin-binding protein, it is likely involved in actin microfilament organization during the epithelial cycle to confer plasticity to the ES in the testis, facilitating the transport of preleptotene spermatocytes across the BTB at stage VIII of the epithelial cycle, as well as the transport of elongating spermatids across the adluminal compartment of the seminiferous epithelium during the epithelial cycle so that step 19 spermatids can line-up near to the tubule lumen to prepare for spermiation at stage VIII of the cycle (Figure 3). This postulate is supported by a study using RNAi to silence ezrin by using ezrin-specific siRNA duplexes versus nontargeting control duplexes.27 When ezrin was knock-down by ~90%, F-actin organization in Sertoli cells with an established functional TJ-permeability barrier that mimic the Sertoli cell BTB in vivo, was found to be perturbed.27 For instance, actin microfilaments in Sertoli cells were shown to be grossly disrupted with extensive truncation, which is likely mediated via a mislocalization and down-regulation of palladin,27 which an actin cross-linking and bundling protein in the testis.51 These changes thus destabilized adhesion proteins at the Sertoli cell-cell interface, such as N-cadherin, which used actin for attachment, as such, the Sertoli cell TJ-permeability barrier function was disrupted.27


Ezrin: a regulator of actin microfilaments in cell junctions of the rat testis.

Gungor-Ordueri NE, Celik-Ozenci C, Cheng CY - Asian J. Androl. (2015 Jul-Aug)

A schematic drawing illustrating the likely role of ezrin in the apical ectoplasmic specialization (ES) during the epithelial cycle in the rat testis. Ezrin is an actin-binding protein at the ES but restrictively expressed at the apical ES at stage VIII of the epithelial cycle, which is robustly expressed at early VIII and begins to diminish by late VIII,27 as depicted herein. At early stage VIII (left panel), ezrin likely recruits actin regulatory proteins to the apical ES, such as actin-related protein 3 (Arp3) to initiate actin microfilament re-organization, such as by converting bundled microfilaments to an unbundled and branched network to facilitate endocytic vesicle-mediated protein trafficing, such as endocytosis, transcytosis and recycling, which in turn facilitates the assembly of new apical when step 8 spermatids arise at this stage. At late stage VIII (right panel), the expression of ezrin diminishes considerably,27 and a knockdown of ezrin has shown that a transient loss of ezrin in Sertoli cells leads to actin microfilament truncation and defragmentation, likely the result of Arp2/3-mediated actin re-organization, coupled with a mis-localization of actin bundling protein palladin.27 This thus further potentiates apical ES restructuring, facilitating the release of sperms at spermiation. Furthermore, MMP2-mediated degration of laminin chains generate biologically active peptide fragments to induce blood-testis barrier (BTB) restructuring,5758 coordinating the events of spermation and BTB remodeling at stage VIII of the cycle. It is noted that this is a hypothetical model, and much research is needed to confirm this concept. However, it serves as a working model for future investigations as discussed in text.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4492059&req=5

Figure 3: A schematic drawing illustrating the likely role of ezrin in the apical ectoplasmic specialization (ES) during the epithelial cycle in the rat testis. Ezrin is an actin-binding protein at the ES but restrictively expressed at the apical ES at stage VIII of the epithelial cycle, which is robustly expressed at early VIII and begins to diminish by late VIII,27 as depicted herein. At early stage VIII (left panel), ezrin likely recruits actin regulatory proteins to the apical ES, such as actin-related protein 3 (Arp3) to initiate actin microfilament re-organization, such as by converting bundled microfilaments to an unbundled and branched network to facilitate endocytic vesicle-mediated protein trafficing, such as endocytosis, transcytosis and recycling, which in turn facilitates the assembly of new apical when step 8 spermatids arise at this stage. At late stage VIII (right panel), the expression of ezrin diminishes considerably,27 and a knockdown of ezrin has shown that a transient loss of ezrin in Sertoli cells leads to actin microfilament truncation and defragmentation, likely the result of Arp2/3-mediated actin re-organization, coupled with a mis-localization of actin bundling protein palladin.27 This thus further potentiates apical ES restructuring, facilitating the release of sperms at spermiation. Furthermore, MMP2-mediated degration of laminin chains generate biologically active peptide fragments to induce blood-testis barrier (BTB) restructuring,5758 coordinating the events of spermation and BTB remodeling at stage VIII of the cycle. It is noted that this is a hypothetical model, and much research is needed to confirm this concept. However, it serves as a working model for future investigations as discussed in text.
Mentions: Ezrin was first reported in the mouse testis by fluorescence microscopy, illustrating it is expressed by Sertoli and germ cells, associated with actin microfilaments, involved in spermiogenesis and the maturation of Sertoli cells.26 Besides expressed predominantly at the Sertoli cell-step 16 spermatid interface in the mouse testis during the epithelial cycle, ezrin is notably expressed in the ultrastructure of residual bodies at stage VIII of the epithelial cycle.26 In humans, ezrin was found to be associated with spermatozoa, involving in sperm capacitation, possibly due to its role in maintaining the actin-based cytoskeleton and the associated proteins necessary to confer capacitation.28 A recent study has shown that ezrin is indeed an actin-binding protein in the rat testis,27 consistent with an earlier report by immunoprecipitation, illustrating ezrin binds to actin microfilaments in the mouse testis.26 Besides interacting with actin in Sertoli cells (Figure 2), ezrin also binds to Arp3 (which together Arp2 forms the Arp2/3 complex, and when it is activated by neuronal Wiskott–Aldrich Syndrome protein (N-WASP), the Arp2/3-N-WASP complex is known to induce barbed end nucleation, causing branched actin polymerization,4950 effectively converting actin microfilaments from a “bundled” to an “unbundled/branched” configuration), JAM-A, N-cadherin, c-Src and p-FAK-Tyr397.27 These findings are important since they illustrate the possibility that ezrin, besides an actin-binding protein, it is likely involved in actin microfilament organization during the epithelial cycle to confer plasticity to the ES in the testis, facilitating the transport of preleptotene spermatocytes across the BTB at stage VIII of the epithelial cycle, as well as the transport of elongating spermatids across the adluminal compartment of the seminiferous epithelium during the epithelial cycle so that step 19 spermatids can line-up near to the tubule lumen to prepare for spermiation at stage VIII of the cycle (Figure 3). This postulate is supported by a study using RNAi to silence ezrin by using ezrin-specific siRNA duplexes versus nontargeting control duplexes.27 When ezrin was knock-down by ~90%, F-actin organization in Sertoli cells with an established functional TJ-permeability barrier that mimic the Sertoli cell BTB in vivo, was found to be perturbed.27 For instance, actin microfilaments in Sertoli cells were shown to be grossly disrupted with extensive truncation, which is likely mediated via a mislocalization and down-regulation of palladin,27 which an actin cross-linking and bundling protein in the testis.51 These changes thus destabilized adhesion proteins at the Sertoli cell-cell interface, such as N-cadherin, which used actin for attachment, as such, the Sertoli cell TJ-permeability barrier function was disrupted.27

Bottom Line: Thus, these proteins are crucial to confer integrity of the apical membrane domain and its associated junctional complex, namely the tight junction and the adherens junction.Since ectoplasmic specialization (ES) is an F-actin-rich testis-specific anchoring junction-a highly dynamic ultrastructure in the seminiferous epithelium due to continuous transport of germ cells, in particular spermatids, across the epithelium during the epithelial cycle-it is conceivable that ERM proteins are playing an active role in these events.Although these proteins were first reported almost 25 years and have since been extensively studied in multiple epithelia/endothelia, few reports are found in the literature to examine their role in the actin filament bundles at the ES.

View Article: PubMed Central - PubMed

Affiliation: The Mary M. Wohlford Laboratory for Male Contraceptive Research, Center for Biomedical Research, Population Council, New York, USA.

ABSTRACT
Ezrin, radixin, moesin and merlin (ERM) proteins are highly homologous actin-binding proteins that share extensive sequence similarity with each other. These proteins tether integral membrane proteins and their cytoplasmic peripheral proteins (e.g., adaptors, nonreceptor protein kinases and phosphatases) to the microfilaments of actin-based cytoskeleton. Thus, these proteins are crucial to confer integrity of the apical membrane domain and its associated junctional complex, namely the tight junction and the adherens junction. Since ectoplasmic specialization (ES) is an F-actin-rich testis-specific anchoring junction-a highly dynamic ultrastructure in the seminiferous epithelium due to continuous transport of germ cells, in particular spermatids, across the epithelium during the epithelial cycle-it is conceivable that ERM proteins are playing an active role in these events. Although these proteins were first reported almost 25 years and have since been extensively studied in multiple epithelia/endothelia, few reports are found in the literature to examine their role in the actin filament bundles at the ES. Studies have shown that ezrin is also a constituent protein of the actin-based tunneling nanotubes (TNT) also known as intercellular bridges, which are transient cytoplasmic tubular ultrastructures that transport signals, molecules and even organelles between adjacent and distant cells in an epithelium to coordinate cell events that occur across an epithelium. Herein, we critically evaluate recent data on ERM in light of recent findings in the field in particular ezrin regarding its role in actin dynamics at the ES in the testis, illustrating additional studies are warranted to examine its physiological significance in spermatogenesis.

No MeSH data available.


Related in: MedlinePlus