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Actin cross-linking protein palladin and spermatogenesis.

Qian X, Mruk DD, Cheng YH, Cheng CY - Spermatogenesis (2013)

Bottom Line: Herein, we summarize some of the latest findings in the field regarding a novel actin cross-linker and actin-bundling protein called palladin.We also discuss in this opinion article the likely role of palladin in regulating actin filament bundles at the ES during spermatogenesis, highlighting the significant of palladin and how this protein is plausibly working in concert with other actin-binding/regulatory proteins and components of polarity proteins to regulate the cyclic events of actin organization and re-organization during the epithelial cycle of spermatogenesis.We also propose a hypothetic model by which palladin regulates ES restructuring during the epithelial cycle of spermatogenesis.

View Article: PubMed Central - PubMed

Affiliation: The Mary M. Wohlford Laboratory for Male Contraceptive Research; Center for Biomedical Research; Population Council; New York, NY USA ; School of Basic Medicine; Peking Union Medical College; Beijing, China.

ABSTRACT
In the seminiferous epithelium of the mammalian testis, the most distinctive ultrastructure is the extensive bundles of actin filaments that lie near the Sertoli-spermatid interface and the Sertoli-Sertoli cell interface known as the apical ectoplasmic specialization (apical ES) and the basal ES, respectively. These actin filament bundles not only confer strong adhesion at these sites, they are uniquely found in the testis. Recent studies have shown that ES also confers spermatid and Sertoli cell polarity in the seminiferous epithelium during the epithelial cycle. While these junctions were first described in the 1970s, there are few functional studies in the literature to examine the regulation of these actin filament bundles. It is conceivable that these actin filament bundles at the ES undergo extensive re-organization to accommodate changes in location of developing spermatids during spermiogenesis as spermatids are transported across the seminiferous epithelium. Additionally, these actin filaments are rapidly reorganized during BTB restructuring to accommodate the transit of preleptotene spermatocytes across the barrier at stage VIII of the epithelial cycle. Thus, actin binding and regulatory proteins are likely involved in these events to confer changes in F-actin organization at these sites. Interestingly, there are no reports in the field to study these regulatory proteins until recently. Herein, we summarize some of the latest findings in the field regarding a novel actin cross-linker and actin-bundling protein called palladin. We also discuss in this opinion article the likely role of palladin in regulating actin filament bundles at the ES during spermatogenesis, highlighting the significant of palladin and how this protein is plausibly working in concert with other actin-binding/regulatory proteins and components of polarity proteins to regulate the cyclic events of actin organization and re-organization during the epithelial cycle of spermatogenesis. We also propose a hypothetic model by which palladin regulates ES restructuring during the epithelial cycle of spermatogenesis.

No MeSH data available.


Related in: MedlinePlus

Figure 2. Stage-specific localization and expression of palladin in the seminiferous epithelium of adult rat testes. Palladin (red fluorescence) was localized to the tunica propria, associated with peritubular myoid cells and also near the basement membrane, consistent with its localization at the BTB. (A) Most notably, palladin was localized at the apical ES, surrounding the head of elongating spermatids, in step 15–19 spermatids at stage I‒VIII of the epithelial cycle. More importantly, its localization at the apical ES altered during the progression of spermiogenesis. For instance, at stage I‒V, palladin was found to surround the entire spermatid head, but it shifted mostly to the tip of the spermatid head beginning at stage VII, and most obvious at stage VIII, illustrating that palladin is no longer needed to confer the actin filament bundles at stage VIII in preparation for the release of sperm at spermiation. Immunofluorescence microscopy was performed as described in reference 10 using a rabbit anti-palladin antibody (Protein Tech, Cat. # 10853–1-AP, working dilution, 1:100), spermatid nuclei were visualized by DAPI (4’,6-diamidino-2-phenylindole) staining. For each staged tubule, the “yellow” boxed area on the left was magnified and shown on the right, scale bar = 50 μm in the micrograph on the left, and scale bar = 10 μm in the micrograph enlarged on the right, which apply to corresponding micrographs in all other stages. These observations support the notion that palladin is involved in conferring changes in the organization of F-actin filaments from their “bundles” and “de-bundled” configuration to facilitate spermatid transport across the seminiferous epithelium as well as changes in the shape/morphology of the spermatid head, as well as spermatid polarity during spermiogenesis. (B) Palladin (red fluorescence) was also found to co-localize with F-actin at the BTB besides the tunica propriate (F-actin was detected by using phalloidin-FITC) (Sigma-Aldrich, Cat. # P5282; working dilution, 1:70). Bar = 10 μm in the micrograph on the left, which apply to corresponding micrographs in this panel.
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Figure 2: Figure 2. Stage-specific localization and expression of palladin in the seminiferous epithelium of adult rat testes. Palladin (red fluorescence) was localized to the tunica propria, associated with peritubular myoid cells and also near the basement membrane, consistent with its localization at the BTB. (A) Most notably, palladin was localized at the apical ES, surrounding the head of elongating spermatids, in step 15–19 spermatids at stage I‒VIII of the epithelial cycle. More importantly, its localization at the apical ES altered during the progression of spermiogenesis. For instance, at stage I‒V, palladin was found to surround the entire spermatid head, but it shifted mostly to the tip of the spermatid head beginning at stage VII, and most obvious at stage VIII, illustrating that palladin is no longer needed to confer the actin filament bundles at stage VIII in preparation for the release of sperm at spermiation. Immunofluorescence microscopy was performed as described in reference 10 using a rabbit anti-palladin antibody (Protein Tech, Cat. # 10853–1-AP, working dilution, 1:100), spermatid nuclei were visualized by DAPI (4’,6-diamidino-2-phenylindole) staining. For each staged tubule, the “yellow” boxed area on the left was magnified and shown on the right, scale bar = 50 μm in the micrograph on the left, and scale bar = 10 μm in the micrograph enlarged on the right, which apply to corresponding micrographs in all other stages. These observations support the notion that palladin is involved in conferring changes in the organization of F-actin filaments from their “bundles” and “de-bundled” configuration to facilitate spermatid transport across the seminiferous epithelium as well as changes in the shape/morphology of the spermatid head, as well as spermatid polarity during spermiogenesis. (B) Palladin (red fluorescence) was also found to co-localize with F-actin at the BTB besides the tunica propriate (F-actin was detected by using phalloidin-FITC) (Sigma-Aldrich, Cat. # P5282; working dilution, 1:70). Bar = 10 μm in the micrograph on the left, which apply to corresponding micrographs in this panel.

Mentions: The 90 kDa isoform of palladin, an actin cross-linker and an actin-bundling protein, was detected both at the apical ES and at the basal ES at the BTB in adult rat testes, highly expressed by Sertoli and germ cells.10 Furthermore, palladin was almost exclusively localized to the apical ES and the basal ES at the BTB,10 the F-actin-rich ultrastructures in the seminiferous epithelium that require changes in their organization from their “bundled” to “de-bundled” configuration and vice versa during the epithelial cycle. Also, palladin was also detected at the tunica propria, apparently associated with peritubular myoid cells.10 Most notably, the localization of palladin at the apical ES surrounding the heads of spermatids changes considerably during spermiogenesis, such as from stages I‒II, IV‒V, VI‒VII, VIII and XII‒XIII when step 15–16, 17, 18–19, 19 and 12–13, respectively, are found in the adluminal compartment (Fig. 2), reflecting the need of the apical ES to undergo extensive re-organization of the actin filament bundles at the site to accommodate spermatid transport across the epithelium, which also coupled with changes in the morphology of spermatid head (e.g., packaging of the genetic materials in the spermatid nucleus in the head region, formation of acrosome) and spermatid polarity. Thus, palladin is working in conjunction with other actin-binding and regulatory proteins, such as Eps 8, Arp2/3 complex, drebrin E, filamin A and perhaps other yet-to-be identified actin regulatory proteins, to confer changes of the actin filament bundles by altering between the “bundled” and “de-bundled” configuration. For instance, spermatids have to be transported from near the basement membrane toward the adluminal edge of the tubule at stages I‒IV, but also be transported back to the basal compartment by almost touching the Sertoli cell nucleus located in the basal compartment at stage V, and then transported back up to the adluminal compartment at stages VI‒VII until they line up at the luminal edge near the tubule lumen at early stage VIII with their heads pointing toward the basement membrane and their tails to the tubule lumen in highly polarized fashion to prepare for spermiation.52-54


Actin cross-linking protein palladin and spermatogenesis.

Qian X, Mruk DD, Cheng YH, Cheng CY - Spermatogenesis (2013)

Figure 2. Stage-specific localization and expression of palladin in the seminiferous epithelium of adult rat testes. Palladin (red fluorescence) was localized to the tunica propria, associated with peritubular myoid cells and also near the basement membrane, consistent with its localization at the BTB. (A) Most notably, palladin was localized at the apical ES, surrounding the head of elongating spermatids, in step 15–19 spermatids at stage I‒VIII of the epithelial cycle. More importantly, its localization at the apical ES altered during the progression of spermiogenesis. For instance, at stage I‒V, palladin was found to surround the entire spermatid head, but it shifted mostly to the tip of the spermatid head beginning at stage VII, and most obvious at stage VIII, illustrating that palladin is no longer needed to confer the actin filament bundles at stage VIII in preparation for the release of sperm at spermiation. Immunofluorescence microscopy was performed as described in reference 10 using a rabbit anti-palladin antibody (Protein Tech, Cat. # 10853–1-AP, working dilution, 1:100), spermatid nuclei were visualized by DAPI (4’,6-diamidino-2-phenylindole) staining. For each staged tubule, the “yellow” boxed area on the left was magnified and shown on the right, scale bar = 50 μm in the micrograph on the left, and scale bar = 10 μm in the micrograph enlarged on the right, which apply to corresponding micrographs in all other stages. These observations support the notion that palladin is involved in conferring changes in the organization of F-actin filaments from their “bundles” and “de-bundled” configuration to facilitate spermatid transport across the seminiferous epithelium as well as changes in the shape/morphology of the spermatid head, as well as spermatid polarity during spermiogenesis. (B) Palladin (red fluorescence) was also found to co-localize with F-actin at the BTB besides the tunica propriate (F-actin was detected by using phalloidin-FITC) (Sigma-Aldrich, Cat. # P5282; working dilution, 1:70). Bar = 10 μm in the micrograph on the left, which apply to corresponding micrographs in this panel.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
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Figure 2: Figure 2. Stage-specific localization and expression of palladin in the seminiferous epithelium of adult rat testes. Palladin (red fluorescence) was localized to the tunica propria, associated with peritubular myoid cells and also near the basement membrane, consistent with its localization at the BTB. (A) Most notably, palladin was localized at the apical ES, surrounding the head of elongating spermatids, in step 15–19 spermatids at stage I‒VIII of the epithelial cycle. More importantly, its localization at the apical ES altered during the progression of spermiogenesis. For instance, at stage I‒V, palladin was found to surround the entire spermatid head, but it shifted mostly to the tip of the spermatid head beginning at stage VII, and most obvious at stage VIII, illustrating that palladin is no longer needed to confer the actin filament bundles at stage VIII in preparation for the release of sperm at spermiation. Immunofluorescence microscopy was performed as described in reference 10 using a rabbit anti-palladin antibody (Protein Tech, Cat. # 10853–1-AP, working dilution, 1:100), spermatid nuclei were visualized by DAPI (4’,6-diamidino-2-phenylindole) staining. For each staged tubule, the “yellow” boxed area on the left was magnified and shown on the right, scale bar = 50 μm in the micrograph on the left, and scale bar = 10 μm in the micrograph enlarged on the right, which apply to corresponding micrographs in all other stages. These observations support the notion that palladin is involved in conferring changes in the organization of F-actin filaments from their “bundles” and “de-bundled” configuration to facilitate spermatid transport across the seminiferous epithelium as well as changes in the shape/morphology of the spermatid head, as well as spermatid polarity during spermiogenesis. (B) Palladin (red fluorescence) was also found to co-localize with F-actin at the BTB besides the tunica propriate (F-actin was detected by using phalloidin-FITC) (Sigma-Aldrich, Cat. # P5282; working dilution, 1:70). Bar = 10 μm in the micrograph on the left, which apply to corresponding micrographs in this panel.
Mentions: The 90 kDa isoform of palladin, an actin cross-linker and an actin-bundling protein, was detected both at the apical ES and at the basal ES at the BTB in adult rat testes, highly expressed by Sertoli and germ cells.10 Furthermore, palladin was almost exclusively localized to the apical ES and the basal ES at the BTB,10 the F-actin-rich ultrastructures in the seminiferous epithelium that require changes in their organization from their “bundled” to “de-bundled” configuration and vice versa during the epithelial cycle. Also, palladin was also detected at the tunica propria, apparently associated with peritubular myoid cells.10 Most notably, the localization of palladin at the apical ES surrounding the heads of spermatids changes considerably during spermiogenesis, such as from stages I‒II, IV‒V, VI‒VII, VIII and XII‒XIII when step 15–16, 17, 18–19, 19 and 12–13, respectively, are found in the adluminal compartment (Fig. 2), reflecting the need of the apical ES to undergo extensive re-organization of the actin filament bundles at the site to accommodate spermatid transport across the epithelium, which also coupled with changes in the morphology of spermatid head (e.g., packaging of the genetic materials in the spermatid nucleus in the head region, formation of acrosome) and spermatid polarity. Thus, palladin is working in conjunction with other actin-binding and regulatory proteins, such as Eps 8, Arp2/3 complex, drebrin E, filamin A and perhaps other yet-to-be identified actin regulatory proteins, to confer changes of the actin filament bundles by altering between the “bundled” and “de-bundled” configuration. For instance, spermatids have to be transported from near the basement membrane toward the adluminal edge of the tubule at stages I‒IV, but also be transported back to the basal compartment by almost touching the Sertoli cell nucleus located in the basal compartment at stage V, and then transported back up to the adluminal compartment at stages VI‒VII until they line up at the luminal edge near the tubule lumen at early stage VIII with their heads pointing toward the basement membrane and their tails to the tubule lumen in highly polarized fashion to prepare for spermiation.52-54

Bottom Line: Herein, we summarize some of the latest findings in the field regarding a novel actin cross-linker and actin-bundling protein called palladin.We also discuss in this opinion article the likely role of palladin in regulating actin filament bundles at the ES during spermatogenesis, highlighting the significant of palladin and how this protein is plausibly working in concert with other actin-binding/regulatory proteins and components of polarity proteins to regulate the cyclic events of actin organization and re-organization during the epithelial cycle of spermatogenesis.We also propose a hypothetic model by which palladin regulates ES restructuring during the epithelial cycle of spermatogenesis.

View Article: PubMed Central - PubMed

Affiliation: The Mary M. Wohlford Laboratory for Male Contraceptive Research; Center for Biomedical Research; Population Council; New York, NY USA ; School of Basic Medicine; Peking Union Medical College; Beijing, China.

ABSTRACT
In the seminiferous epithelium of the mammalian testis, the most distinctive ultrastructure is the extensive bundles of actin filaments that lie near the Sertoli-spermatid interface and the Sertoli-Sertoli cell interface known as the apical ectoplasmic specialization (apical ES) and the basal ES, respectively. These actin filament bundles not only confer strong adhesion at these sites, they are uniquely found in the testis. Recent studies have shown that ES also confers spermatid and Sertoli cell polarity in the seminiferous epithelium during the epithelial cycle. While these junctions were first described in the 1970s, there are few functional studies in the literature to examine the regulation of these actin filament bundles. It is conceivable that these actin filament bundles at the ES undergo extensive re-organization to accommodate changes in location of developing spermatids during spermiogenesis as spermatids are transported across the seminiferous epithelium. Additionally, these actin filaments are rapidly reorganized during BTB restructuring to accommodate the transit of preleptotene spermatocytes across the barrier at stage VIII of the epithelial cycle. Thus, actin binding and regulatory proteins are likely involved in these events to confer changes in F-actin organization at these sites. Interestingly, there are no reports in the field to study these regulatory proteins until recently. Herein, we summarize some of the latest findings in the field regarding a novel actin cross-linker and actin-bundling protein called palladin. We also discuss in this opinion article the likely role of palladin in regulating actin filament bundles at the ES during spermatogenesis, highlighting the significant of palladin and how this protein is plausibly working in concert with other actin-binding/regulatory proteins and components of polarity proteins to regulate the cyclic events of actin organization and re-organization during the epithelial cycle of spermatogenesis. We also propose a hypothetic model by which palladin regulates ES restructuring during the epithelial cycle of spermatogenesis.

No MeSH data available.


Related in: MedlinePlus