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Xenopus importin beta validates human importin beta as a cell cycle negative regulator
Valerie A Delmar1, Rene C Chan, Douglass J Forbes
1Section of Cell and Developmental Biology, Division of Biological Sciences 0347, University of California - San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0347, USA. vadelmar@yahoo.com
BMC Cell Biology
|March 28, 2008
Summary
Importin beta, in both human and Xenopus forms, authenticates as a negative regulator for nuclear assembly. Its inhibition of nuclear pore assembly is Ran-reversible when untagged, offering insights into nuclear pore formation.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Human importin beta is widely used in Xenopus laevis cell cycle studies, raising questions about its regulatory role due to species differences.
- The authentic function of importin beta as a negative regulator of cell cycle events was uncertain.
- The Xenopus importin beta gene had not been identified, necessitating its cloning and characterization.
Purpose of the Study:
- To clone and identify the Xenopus importin beta gene.
- To compare the regulatory effects of human and Xenopus importin beta on nuclear assembly.
- To determine if importin beta is an authentic negative regulator or a dominant negative mutant.
Main Methods:
- Cloning and identification of the Xenopus importin beta gene.
- In vitro studies of nuclear membrane fusion and pore assembly using human and Xenopus importin beta.
- Investigating the effect of Ran on importin beta-mediated inhibition of nuclear pore assembly with tagged and untagged proteins.
Main Results:
- Xenopus importin beta demonstrated identical negative regulatory effects on nuclear membrane fusion and pore assembly as human importin beta.
- Inhibition of nuclear pore assembly by importin beta was found to be Ran-reversible when untagged versions of either human or Xenopus importin beta were used.
- A difference in Ran sensitivity was observed between tagged and untagged importin beta in the context of nuclear pore assembly.
Conclusions:
- Importin beta, from both human and Xenopus species, functions as an authentic negative regulator of nuclear and spindle assembly.
- The Ran-reversible nature of nuclear pore assembly inhibition by untagged importin beta provides mechanistic insights into nuclear pore formation.
- The study clarifies the role of importin beta in nuclear assembly, resolving previous ambiguities arising from species-specific usage.
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