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Hof1 and Rvs167 have redundant roles in actomyosin ring function during cytokinesis in budding yeast.

Nkosi PJ, Targosz BS, Labib K, Sanchez-Diaz A - PLoS ONE (2013)

Bottom Line: This new function of Rvs167 appears to be independent of its known role as a regulator of the Arp2/3 actin nucleator, as actin ring assembly is not abolished by the simultaneous inactivation of Hof1 and Arp2/3.Instead we find that recruitment to the bud-neck of the Iqg1 actin regulator is defective in cells lacking Hof1 and Rvs167, though future studies will be needed to determine if this reflects a direct interaction between these factors.The redundant role of Hof1 in actin ring assembly suggests that the mechanism of actin ring assembly has been conserved to a greater extent across evolution than anticipated previously.

View Article: PubMed Central - PubMed

Affiliation: Paterson Institute for Cancer Research, University of Manchester, Manchester, United Kingdom.

ABSTRACT
The Hof1 protein (Homologue of Fifteen) regulates formation of the primary septum during cytokinesis in the budding yeast Saccharomyces cerevisiae, whereas the orthologous Cdc15 protein in fission yeast regulates the actomyosin ring by using its F-BAR domain to recruit actin nucleators to the cleavage site. Here we show that budding yeast Hof1 also contributes to actin ring assembly in parallel with the Rvs167 protein. Simultaneous deletion of the HOF1 and RVS167 genes is lethal, and cells fail to assemble the actomyosin ring as they progress through mitosis. Although Hof1 and Rvs167 are not orthologues, they both share an analogous structure, with an F-BAR or BAR domain at the amino terminus, capable of inducing membrane curvature, and SH3 domains at the carboxyl terminus that bind to specific proline-rich targets. The SH3 domain of Rvs167 becomes essential for assembly of the actomyosin ring in cells lacking Hof1, suggesting that it helps to recruit a regulator of the actin cytoskeleton. This new function of Rvs167 appears to be independent of its known role as a regulator of the Arp2/3 actin nucleator, as actin ring assembly is not abolished by the simultaneous inactivation of Hof1 and Arp2/3. Instead we find that recruitment to the bud-neck of the Iqg1 actin regulator is defective in cells lacking Hof1 and Rvs167, though future studies will be needed to determine if this reflects a direct interaction between these factors. The redundant role of Hof1 in actin ring assembly suggests that the mechanism of actin ring assembly has been conserved to a greater extent across evolution than anticipated previously.

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Recruitment of Inn1 to the bud-neck is defective in the complete absence of Hof1 and Rvs167.(A) The indicated strains were synchronised in G1 phase at 24°C, before expression of GAL-UBR1 (Ubr1 is the E3 ligase for N-end rule pathway that mediates ubiquitylation of the heat inducible degron) and degradation of Hof1-td and Cyk3-td at 37°C. Cells were then released from G1 arrest and samples taken at the indicated times to determine the proportion of bi-nucleate cells (i) and the percentage of cells with rings or spots of Inn1 at the bud-neck (ii), as cells completed the cell cycle. (B) Images from the experiment described in (A). The Inn1-GFP rings in hof1-td cyk3-td were frequently less bright than those observed in control cells. The scale bars correspond to 2 µm.
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pone-0057846-g004: Recruitment of Inn1 to the bud-neck is defective in the complete absence of Hof1 and Rvs167.(A) The indicated strains were synchronised in G1 phase at 24°C, before expression of GAL-UBR1 (Ubr1 is the E3 ligase for N-end rule pathway that mediates ubiquitylation of the heat inducible degron) and degradation of Hof1-td and Cyk3-td at 37°C. Cells were then released from G1 arrest and samples taken at the indicated times to determine the proportion of bi-nucleate cells (i) and the percentage of cells with rings or spots of Inn1 at the bud-neck (ii), as cells completed the cell cycle. (B) Images from the experiment described in (A). The Inn1-GFP rings in hof1-td cyk3-td were frequently less bright than those observed in control cells. The scale bars correspond to 2 µm.

Mentions: Inn1 must be recruited to the bud-neck at the end of mitosis to activate chitin synthase II, and recruitment of Inn1 is jointly dependent upon Hof1 and the integrity of the actomyosin ring [23], [25]. It seemed possible that Rvs167 might not have a direct role in recruitment of Inn1, as the hof1-ΔSH3 allele is not synthetic lethal with rvs167Δ (Figure 1E), and we found that Inn1 was still recruited to the budneck at the end of mitosis in hof1-ΔSH3 rvs167-ΔSH3 cells that are viable at 24°C (Figure 3). Surprisingly, however, we found that recruitment of Inn1 to the bud-neck was greatly defective in the complete absence of Rvs167 and Hof1. Whereas Inn1 appeared at the bud-neck during late mitosis in control cells, or following the rapid depletion of Hof1 and Cyk3 in cells with both proteins fused to the heat inducible degron [39], [40], recruitment of Inn1 was severely compromised in hof1-td rvs167Δ cells and abolished in hof1-td cyk3-td rvs167Δ (Figure 4A-B; td  =  temperature sensitive degron), despite equivalent defects in cell division in all three strains that lacked Hof1 at 37°C (Figure 4A (i)).


Hof1 and Rvs167 have redundant roles in actomyosin ring function during cytokinesis in budding yeast.

Nkosi PJ, Targosz BS, Labib K, Sanchez-Diaz A - PLoS ONE (2013)

Recruitment of Inn1 to the bud-neck is defective in the complete absence of Hof1 and Rvs167.(A) The indicated strains were synchronised in G1 phase at 24°C, before expression of GAL-UBR1 (Ubr1 is the E3 ligase for N-end rule pathway that mediates ubiquitylation of the heat inducible degron) and degradation of Hof1-td and Cyk3-td at 37°C. Cells were then released from G1 arrest and samples taken at the indicated times to determine the proportion of bi-nucleate cells (i) and the percentage of cells with rings or spots of Inn1 at the bud-neck (ii), as cells completed the cell cycle. (B) Images from the experiment described in (A). The Inn1-GFP rings in hof1-td cyk3-td were frequently less bright than those observed in control cells. The scale bars correspond to 2 µm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3585203&req=5

pone-0057846-g004: Recruitment of Inn1 to the bud-neck is defective in the complete absence of Hof1 and Rvs167.(A) The indicated strains were synchronised in G1 phase at 24°C, before expression of GAL-UBR1 (Ubr1 is the E3 ligase for N-end rule pathway that mediates ubiquitylation of the heat inducible degron) and degradation of Hof1-td and Cyk3-td at 37°C. Cells were then released from G1 arrest and samples taken at the indicated times to determine the proportion of bi-nucleate cells (i) and the percentage of cells with rings or spots of Inn1 at the bud-neck (ii), as cells completed the cell cycle. (B) Images from the experiment described in (A). The Inn1-GFP rings in hof1-td cyk3-td were frequently less bright than those observed in control cells. The scale bars correspond to 2 µm.
Mentions: Inn1 must be recruited to the bud-neck at the end of mitosis to activate chitin synthase II, and recruitment of Inn1 is jointly dependent upon Hof1 and the integrity of the actomyosin ring [23], [25]. It seemed possible that Rvs167 might not have a direct role in recruitment of Inn1, as the hof1-ΔSH3 allele is not synthetic lethal with rvs167Δ (Figure 1E), and we found that Inn1 was still recruited to the budneck at the end of mitosis in hof1-ΔSH3 rvs167-ΔSH3 cells that are viable at 24°C (Figure 3). Surprisingly, however, we found that recruitment of Inn1 to the bud-neck was greatly defective in the complete absence of Rvs167 and Hof1. Whereas Inn1 appeared at the bud-neck during late mitosis in control cells, or following the rapid depletion of Hof1 and Cyk3 in cells with both proteins fused to the heat inducible degron [39], [40], recruitment of Inn1 was severely compromised in hof1-td rvs167Δ cells and abolished in hof1-td cyk3-td rvs167Δ (Figure 4A-B; td  =  temperature sensitive degron), despite equivalent defects in cell division in all three strains that lacked Hof1 at 37°C (Figure 4A (i)).

Bottom Line: This new function of Rvs167 appears to be independent of its known role as a regulator of the Arp2/3 actin nucleator, as actin ring assembly is not abolished by the simultaneous inactivation of Hof1 and Arp2/3.Instead we find that recruitment to the bud-neck of the Iqg1 actin regulator is defective in cells lacking Hof1 and Rvs167, though future studies will be needed to determine if this reflects a direct interaction between these factors.The redundant role of Hof1 in actin ring assembly suggests that the mechanism of actin ring assembly has been conserved to a greater extent across evolution than anticipated previously.

View Article: PubMed Central - PubMed

Affiliation: Paterson Institute for Cancer Research, University of Manchester, Manchester, United Kingdom.

ABSTRACT
The Hof1 protein (Homologue of Fifteen) regulates formation of the primary septum during cytokinesis in the budding yeast Saccharomyces cerevisiae, whereas the orthologous Cdc15 protein in fission yeast regulates the actomyosin ring by using its F-BAR domain to recruit actin nucleators to the cleavage site. Here we show that budding yeast Hof1 also contributes to actin ring assembly in parallel with the Rvs167 protein. Simultaneous deletion of the HOF1 and RVS167 genes is lethal, and cells fail to assemble the actomyosin ring as they progress through mitosis. Although Hof1 and Rvs167 are not orthologues, they both share an analogous structure, with an F-BAR or BAR domain at the amino terminus, capable of inducing membrane curvature, and SH3 domains at the carboxyl terminus that bind to specific proline-rich targets. The SH3 domain of Rvs167 becomes essential for assembly of the actomyosin ring in cells lacking Hof1, suggesting that it helps to recruit a regulator of the actin cytoskeleton. This new function of Rvs167 appears to be independent of its known role as a regulator of the Arp2/3 actin nucleator, as actin ring assembly is not abolished by the simultaneous inactivation of Hof1 and Arp2/3. Instead we find that recruitment to the bud-neck of the Iqg1 actin regulator is defective in cells lacking Hof1 and Rvs167, though future studies will be needed to determine if this reflects a direct interaction between these factors. The redundant role of Hof1 in actin ring assembly suggests that the mechanism of actin ring assembly has been conserved to a greater extent across evolution than anticipated previously.

Show MeSH
Related in: MedlinePlus