Alpha-crystallin expression affects microtubule assembly and prevents their aggregation

FASEB J. 2006 May;20(7):846-57. doi: 10.1096/fj.05-5532com.


The molecular chaperones alphaA- and alphaB-crystallins are important for cell survival and genomic stability and associate with the tubulin cytoskeleton. The mitotic spindle is abnormally assembled in a number of alphaA-/- and alphaB-/- lens epithelial cells. However, no report to date has studied the effect of alpha-crystallin expression on tubulin/microtubule assembly in lens epithelial cells. In the current work we tested the hypothesis that the absence of alphaA- and alphaB-crystallins alters microtubule assembly. Microtubules were reconstituted from freshly dissected explants of wild-type, alphaA-/-, alphaB-/-, and alpha(A/B) -/- (DKO) mouse lens epithelia and examined by electron microscopic and biochemical analyses. The wild-type microtubules were 4 mum long and approximately 25 nm wide and had a characteristic protofilament structure, but alphaB-/- microtubules were 2.5-fold longer. Microtubule-associated proteins (MAPs) extracted from microtubules by washing with salt included transketolase, alpha-enolase, and betaB2-crystallin. In DKO lens epithelial microtubules but not in wild-type, alphaA-/- or alphaB-/- microtubules, extraction of the MAPs gave very long (14-20 microm) "polyfilament" assemblies that were tightly bundled. Addition of exogenous alpha-crystallin (alphaA+ alphaB) was ineffective in preventing polyfilament formation. However, normal microtubule structure could be restored by including MAPs derived from wild-type lens epithelial cells during microtubule reconstitution. Intriguingly, these data suggest that alpha-crystallin may interact with MAPs to inhibit aggregation of microtubules in lens epithelial cells. Sedimentation analysis and 90 degrees light scattering measurements showed that alpha-crystallin suppressed tubulin assembly in vitro. Alpha-crystallin did not have a strong effect on the GTPase activity of purified tubulin. SDS-PAGE analysis showed that alpha-crystallin prevented heat-induced aggregation of tubulin, suggesting that alpha-crystallin may affect microtubule assembly by maintaining the pool of unassembled tubulin.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Epithelium / metabolism
  • Gene Expression Regulation
  • Lens, Crystalline / metabolism
  • Mice
  • Mice, Knockout
  • Microtubule-Associated Proteins / metabolism
  • Microtubules / chemistry*
  • Microtubules / metabolism*
  • Paclitaxel
  • RNA, Messenger / metabolism
  • Tubulin / metabolism
  • alpha-Crystallin A Chain / genetics
  • alpha-Crystallin A Chain / metabolism*
  • alpha-Crystallin B Chain / genetics
  • alpha-Crystallin B Chain / metabolism*


  • Microtubule-Associated Proteins
  • RNA, Messenger
  • Tubulin
  • alpha-Crystallin A Chain
  • alpha-Crystallin B Chain
  • Paclitaxel