Ultrastructural characterization of giant endosomes induced by GTPase-deficient Rab5

Histochem Cell Biol. 2010 Jan;133(1):41-55. doi: 10.1007/s00418-009-0643-8. Epub 2009 Oct 15.


The small GTPase Rab5 controls the fusogenic properties of early endosomes through GTP-dependent recruitment and activation of effector proteins. Expression of a GTPase-defective mutant, Rab5(Q79L), is known to cause formation of enlarged early endosomes. The ability of Rab5-GTP to recruit multiple effectors raises the question whether the Rab5(Q79L)-induced giant endosomes simply represent enlarged early endosomes or whether they have a more complex phenotype. In this report, we have addressed this issue by generating a HEp2 cell line with inducible expression of Rab5(Q79L) and performing ultrastructural analysis of Rab5(Q79L)-induced endosomes. We find that Rab5(Q79L) not only induces formation of enlarged early endosomes but also causes enlargement of later endocytic profiles. Most strikingly, Rab5(Q79L) causes formation of enlarged multivesicular endosomes with a large number of intraluminal vesicles, and endosomes that contain both early and late endocytic markers are frequently observed. In addition, we observe defects in the sorting of the EGF receptor and the transferrin receptor through this compartment.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line, Tumor
  • Endosomes / metabolism
  • Endosomes / ultrastructure*
  • ErbB Receptors / metabolism
  • GTP Phosphohydrolases / deficiency*
  • Humans
  • rab5 GTP-Binding Proteins / metabolism*


  • ErbB Receptors
  • GTP Phosphohydrolases
  • rab5 GTP-Binding Proteins