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Domains controlling cell polarity and proliferation in the Drosophila tumor suppressor Scribble.

Zeitler J, Hsu CP, Dionne H, Bilder D - J. Cell Biol. (2004)

Bottom Line: The PDZ domains, which recruit the LRR to the junctional complex, are dispensable for overall epithelial organization.PDZ domain absence leads to mild polarity defects accompanied by moderate overproliferation, but the PDZ domains alone are insufficient to provide any Scrib function in mutant discs.We suggest a model in which Scrib, via the activity of the LRR, governs proliferation primarily by regulating apicobasal polarity.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA 94720, USA.

ABSTRACT
Cell polarity and cell proliferation can be coupled in animal tissues, but how they are coupled is not understood. In Drosophila imaginal discs, loss of the neoplastic tumor suppressor gene scribble (scrib), which encodes a multidomain scaffolding protein, disrupts epithelial organization and also causes unchecked proliferation. Using an allelic series of mutations along with rescuing transgenes, we have identified domain requirements for polarity, proliferation control, and other Scrib functions. The leucine-rich repeats (LRR) tether Scrib to the plasma membrane, are both necessary and sufficient to organize a polarized epithelial monolayer, and are required for all proliferation control. The PDZ domains, which recruit the LRR to the junctional complex, are dispensable for overall epithelial organization. PDZ domain absence leads to mild polarity defects accompanied by moderate overproliferation, but the PDZ domains alone are insufficient to provide any Scrib function in mutant discs. We suggest a model in which Scrib, via the activity of the LRR, governs proliferation primarily by regulating apicobasal polarity.

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Location of scrib mutations. (A) Amino acid changes in scrib alleles, mapped onto a diagram of the Scrib protein. Red arrows indicate premature termination codons; the green arrow indicates a missense mutation. (B) Conservation of the leucine mutated in scrib 1 (yellow) between LRR 10 of known LAP proteins. Coloring indicates residues with similar properties: purple =100% conservation, blue >85% conservation, green >70% conservation.
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fig4: Location of scrib mutations. (A) Amino acid changes in scrib alleles, mapped onto a diagram of the Scrib protein. Red arrows indicate premature termination codons; the green arrow indicates a missense mutation. (B) Conservation of the leucine mutated in scrib 1 (yellow) between LRR 10 of known LAP proteins. Coloring indicates residues with similar properties: purple =100% conservation, blue >85% conservation, green >70% conservation.

Mentions: Our phenotypic analysis of the scrib allelic series indicates that many of the mutant proteins retain some aspects of WT scrib function, whereas being compromised in others. To identify the molecular lesions associated with each scrib allele, we isolated and sequenced genomic DNA from homozygous animals. Single base pair changes were identified in the coding region of each of the seven alleles (Fig. 4 A). Six of these changes create premature termination codons, and are predicted to cause truncations in the WT 1751–amino acid Scrib protein. scrib 2 alters the third codon to an amber stop, whereas scrib 3 terminates within the 12th LRR. scrib 4 terminates in the midst of PDZ1, whereas scrib 5 terminates between PDZ2 and PDZ3, and scrib 6 in the midst of PDZ4. Because scrib 4 and 6 delete residues in the PDZ ligand binding groove (Doyle et al., 1996), these truncated domains are not expected to be functional. Scrib 7 removes the final 301 amino acids but deletes no conserved domains. In addition to these six premature stop codons, scrib 1 alters leucine 223, in LRR 10, to a glutamine. This leucine is absolutely conserved between LAP protein LRRs (Fig. 4 B), and is predicted to lie in an α-helix on the external surface of the horseshoe-shaped LRR superstructure, opposite the putative binding pocket (Kobe and Kajava, 2001). The scrib alleles thus produce proteins with mutations in, or deletions of, many of the Scrib interaction domains.


Domains controlling cell polarity and proliferation in the Drosophila tumor suppressor Scribble.

Zeitler J, Hsu CP, Dionne H, Bilder D - J. Cell Biol. (2004)

Location of scrib mutations. (A) Amino acid changes in scrib alleles, mapped onto a diagram of the Scrib protein. Red arrows indicate premature termination codons; the green arrow indicates a missense mutation. (B) Conservation of the leucine mutated in scrib 1 (yellow) between LRR 10 of known LAP proteins. Coloring indicates residues with similar properties: purple =100% conservation, blue >85% conservation, green >70% conservation.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172630&req=5

fig4: Location of scrib mutations. (A) Amino acid changes in scrib alleles, mapped onto a diagram of the Scrib protein. Red arrows indicate premature termination codons; the green arrow indicates a missense mutation. (B) Conservation of the leucine mutated in scrib 1 (yellow) between LRR 10 of known LAP proteins. Coloring indicates residues with similar properties: purple =100% conservation, blue >85% conservation, green >70% conservation.
Mentions: Our phenotypic analysis of the scrib allelic series indicates that many of the mutant proteins retain some aspects of WT scrib function, whereas being compromised in others. To identify the molecular lesions associated with each scrib allele, we isolated and sequenced genomic DNA from homozygous animals. Single base pair changes were identified in the coding region of each of the seven alleles (Fig. 4 A). Six of these changes create premature termination codons, and are predicted to cause truncations in the WT 1751–amino acid Scrib protein. scrib 2 alters the third codon to an amber stop, whereas scrib 3 terminates within the 12th LRR. scrib 4 terminates in the midst of PDZ1, whereas scrib 5 terminates between PDZ2 and PDZ3, and scrib 6 in the midst of PDZ4. Because scrib 4 and 6 delete residues in the PDZ ligand binding groove (Doyle et al., 1996), these truncated domains are not expected to be functional. Scrib 7 removes the final 301 amino acids but deletes no conserved domains. In addition to these six premature stop codons, scrib 1 alters leucine 223, in LRR 10, to a glutamine. This leucine is absolutely conserved between LAP protein LRRs (Fig. 4 B), and is predicted to lie in an α-helix on the external surface of the horseshoe-shaped LRR superstructure, opposite the putative binding pocket (Kobe and Kajava, 2001). The scrib alleles thus produce proteins with mutations in, or deletions of, many of the Scrib interaction domains.

Bottom Line: The PDZ domains, which recruit the LRR to the junctional complex, are dispensable for overall epithelial organization.PDZ domain absence leads to mild polarity defects accompanied by moderate overproliferation, but the PDZ domains alone are insufficient to provide any Scrib function in mutant discs.We suggest a model in which Scrib, via the activity of the LRR, governs proliferation primarily by regulating apicobasal polarity.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA 94720, USA.

ABSTRACT
Cell polarity and cell proliferation can be coupled in animal tissues, but how they are coupled is not understood. In Drosophila imaginal discs, loss of the neoplastic tumor suppressor gene scribble (scrib), which encodes a multidomain scaffolding protein, disrupts epithelial organization and also causes unchecked proliferation. Using an allelic series of mutations along with rescuing transgenes, we have identified domain requirements for polarity, proliferation control, and other Scrib functions. The leucine-rich repeats (LRR) tether Scrib to the plasma membrane, are both necessary and sufficient to organize a polarized epithelial monolayer, and are required for all proliferation control. The PDZ domains, which recruit the LRR to the junctional complex, are dispensable for overall epithelial organization. PDZ domain absence leads to mild polarity defects accompanied by moderate overproliferation, but the PDZ domains alone are insufficient to provide any Scrib function in mutant discs. We suggest a model in which Scrib, via the activity of the LRR, governs proliferation primarily by regulating apicobasal polarity.

Show MeSH
Related in: MedlinePlus