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F-actin-based extensions of the head cyst cell adhere to the maturing spermatids to maintain them in a tight bundle and prevent their premature release in Drosophila testis.

Desai BS, Shirolikar S, Ray K - BMC Biol. (2009)

Bottom Line: Disruption of these F-actin based processes was associated with spermatid bundle disassembly and premature sperm release inside the testis.This is likely to regulate mature sperm release into the seminal vesicle.Overall, this process bears resemblance to mammalian spermiation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai, India. bela@tifr.res.in

ABSTRACT

Background: In Drosophila, all the 64 clonally derived spermatocytes differentiate in syncytium inside two somatic-origin cyst cells. They elongate to form slender spermatids, which are individualized and then released into the seminal vesicle. During individualization, differentiating spermatids are organized in a tight bundle inside the cyst, which is expected to play an important role in sperm selection. However, actual significance of this process and its underlying mechanism are unclear.

Results: We show that dynamic F-actin-based processes extend from the head cyst cell at the start of individualization, filling the interstitial space at the rostral ends of the maturing spermatid bundle. In addition to actin, these structures contained lamin, beta-catenin, dynamin, myosin VI and several other filopodial components. Further, pharmacological and genetic analyses showed that cytoskeletal stability and dynamin function are essential for their maintenance. Disruption of these F-actin based processes was associated with spermatid bundle disassembly and premature sperm release inside the testis.

Conclusion: Altogether, our data suggests that the head cyst cell adheres to the maturing spermatid heads through F-actin-based extensions, thus maintaining them in a tight bundle. This is likely to regulate mature sperm release into the seminal vesicle. Overall, this process bears resemblance to mammalian spermiation.

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Related in: MedlinePlus

Mature spermatid heads remain in a tight bundle attached to the testis wall during the coiling stage. (A), (B) Sets of time lapse images of the testis base, expressing the sneaky-GFP transgene [20], were projected together to show the relative movement of the acrosome bundles of a cyst inside the testis. Each frame is labeled with a specific false color as per the list shown in (B). The blue arrows and arrowheads point to the positions of acrosome bundles in the first frame while the white arrows and arrowheads indicate the final position. The arrows indicate the compacted set, which is likely to belong to the post-individualization stages, while the arrowheads indicate the acrosomes of the elongating/pre-individualization stage spermatids. (A) The compacted acrosome bundle (arrows) found near the base of the testis remain confined in the region as indicated by the positions of the blue and white arrow. Some acrosomes (green arrow) are occasionally found to move away from the bundle. This is considered to belong to the defective sperm that are lost during coiling. In comparison the acrosomes of the elongating spermatids (arrowheads) are loosely organized and move rapidly towards the testis base as evident from the positions of the blue and white arrowheads. (B) The mobility of acrosome bundles (blue and white arrows) near the base of the testis increased after 30 minutes of 5 μM vinblastine (vinb ) treatment. (See Additional files 2 and 4 for details.)
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Figure 5: Mature spermatid heads remain in a tight bundle attached to the testis wall during the coiling stage. (A), (B) Sets of time lapse images of the testis base, expressing the sneaky-GFP transgene [20], were projected together to show the relative movement of the acrosome bundles of a cyst inside the testis. Each frame is labeled with a specific false color as per the list shown in (B). The blue arrows and arrowheads point to the positions of acrosome bundles in the first frame while the white arrows and arrowheads indicate the final position. The arrows indicate the compacted set, which is likely to belong to the post-individualization stages, while the arrowheads indicate the acrosomes of the elongating/pre-individualization stage spermatids. (A) The compacted acrosome bundle (arrows) found near the base of the testis remain confined in the region as indicated by the positions of the blue and white arrow. Some acrosomes (green arrow) are occasionally found to move away from the bundle. This is considered to belong to the defective sperm that are lost during coiling. In comparison the acrosomes of the elongating spermatids (arrowheads) are loosely organized and move rapidly towards the testis base as evident from the positions of the blue and white arrowheads. (B) The mobility of acrosome bundles (blue and white arrows) near the base of the testis increased after 30 minutes of 5 μM vinblastine (vinb ) treatment. (See Additional files 2 and 4 for details.)

Mentions: Spermatids are maintained in a tight bundle inside the cyst during individualization and this is predicted to play a critical role in selecting out the improperly developed sperm [4]. Live analysis of acrosome movements inside testis by using the sneaky-GFP [20] further showed that the acrosome movements slow down after they are packed (arrows, Figure 5A, Additional files 2 and 4). This coincided with actin cap formation and, thus, suggested that the actin caps are required to maintain the sperm heads in a tight bundle during individualization. Indeed we noticed that few mature nuclei were left out in every NB in almost all wild-type testes during the coiling stage. Both F-actin and microtubule dynamics play important roles in the filopodia/pseudopodia assembly and maintenance [39-41]. Latrunculin B (lat B) binds to actin monomers and prevents their polymerization and the addition of lat B to cultured cells leads to major disruption of actin cytoskeleton [41]. Similarly, treatments with vinblastine (vinb) leads to microtubule depolymerization in the tissue [42,43]. Therefore, to determine the role of the cytoskeletal elements in actin caps, we treated intact testis with these reagents.


F-actin-based extensions of the head cyst cell adhere to the maturing spermatids to maintain them in a tight bundle and prevent their premature release in Drosophila testis.

Desai BS, Shirolikar S, Ray K - BMC Biol. (2009)

Mature spermatid heads remain in a tight bundle attached to the testis wall during the coiling stage. (A), (B) Sets of time lapse images of the testis base, expressing the sneaky-GFP transgene [20], were projected together to show the relative movement of the acrosome bundles of a cyst inside the testis. Each frame is labeled with a specific false color as per the list shown in (B). The blue arrows and arrowheads point to the positions of acrosome bundles in the first frame while the white arrows and arrowheads indicate the final position. The arrows indicate the compacted set, which is likely to belong to the post-individualization stages, while the arrowheads indicate the acrosomes of the elongating/pre-individualization stage spermatids. (A) The compacted acrosome bundle (arrows) found near the base of the testis remain confined in the region as indicated by the positions of the blue and white arrow. Some acrosomes (green arrow) are occasionally found to move away from the bundle. This is considered to belong to the defective sperm that are lost during coiling. In comparison the acrosomes of the elongating spermatids (arrowheads) are loosely organized and move rapidly towards the testis base as evident from the positions of the blue and white arrowheads. (B) The mobility of acrosome bundles (blue and white arrows) near the base of the testis increased after 30 minutes of 5 μM vinblastine (vinb ) treatment. (See Additional files 2 and 4 for details.)
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2683793&req=5

Figure 5: Mature spermatid heads remain in a tight bundle attached to the testis wall during the coiling stage. (A), (B) Sets of time lapse images of the testis base, expressing the sneaky-GFP transgene [20], were projected together to show the relative movement of the acrosome bundles of a cyst inside the testis. Each frame is labeled with a specific false color as per the list shown in (B). The blue arrows and arrowheads point to the positions of acrosome bundles in the first frame while the white arrows and arrowheads indicate the final position. The arrows indicate the compacted set, which is likely to belong to the post-individualization stages, while the arrowheads indicate the acrosomes of the elongating/pre-individualization stage spermatids. (A) The compacted acrosome bundle (arrows) found near the base of the testis remain confined in the region as indicated by the positions of the blue and white arrow. Some acrosomes (green arrow) are occasionally found to move away from the bundle. This is considered to belong to the defective sperm that are lost during coiling. In comparison the acrosomes of the elongating spermatids (arrowheads) are loosely organized and move rapidly towards the testis base as evident from the positions of the blue and white arrowheads. (B) The mobility of acrosome bundles (blue and white arrows) near the base of the testis increased after 30 minutes of 5 μM vinblastine (vinb ) treatment. (See Additional files 2 and 4 for details.)
Mentions: Spermatids are maintained in a tight bundle inside the cyst during individualization and this is predicted to play a critical role in selecting out the improperly developed sperm [4]. Live analysis of acrosome movements inside testis by using the sneaky-GFP [20] further showed that the acrosome movements slow down after they are packed (arrows, Figure 5A, Additional files 2 and 4). This coincided with actin cap formation and, thus, suggested that the actin caps are required to maintain the sperm heads in a tight bundle during individualization. Indeed we noticed that few mature nuclei were left out in every NB in almost all wild-type testes during the coiling stage. Both F-actin and microtubule dynamics play important roles in the filopodia/pseudopodia assembly and maintenance [39-41]. Latrunculin B (lat B) binds to actin monomers and prevents their polymerization and the addition of lat B to cultured cells leads to major disruption of actin cytoskeleton [41]. Similarly, treatments with vinblastine (vinb) leads to microtubule depolymerization in the tissue [42,43]. Therefore, to determine the role of the cytoskeletal elements in actin caps, we treated intact testis with these reagents.

Bottom Line: Disruption of these F-actin based processes was associated with spermatid bundle disassembly and premature sperm release inside the testis.This is likely to regulate mature sperm release into the seminal vesicle.Overall, this process bears resemblance to mammalian spermiation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai, India. bela@tifr.res.in

ABSTRACT

Background: In Drosophila, all the 64 clonally derived spermatocytes differentiate in syncytium inside two somatic-origin cyst cells. They elongate to form slender spermatids, which are individualized and then released into the seminal vesicle. During individualization, differentiating spermatids are organized in a tight bundle inside the cyst, which is expected to play an important role in sperm selection. However, actual significance of this process and its underlying mechanism are unclear.

Results: We show that dynamic F-actin-based processes extend from the head cyst cell at the start of individualization, filling the interstitial space at the rostral ends of the maturing spermatid bundle. In addition to actin, these structures contained lamin, beta-catenin, dynamin, myosin VI and several other filopodial components. Further, pharmacological and genetic analyses showed that cytoskeletal stability and dynamin function are essential for their maintenance. Disruption of these F-actin based processes was associated with spermatid bundle disassembly and premature sperm release inside the testis.

Conclusion: Altogether, our data suggests that the head cyst cell adheres to the maturing spermatid heads through F-actin-based extensions, thus maintaining them in a tight bundle. This is likely to regulate mature sperm release into the seminal vesicle. Overall, this process bears resemblance to mammalian spermiation.

Show MeSH
Related in: MedlinePlus