Intranuclear endoplasmic reticulum induced by Nopp140 mimics the nucleolar channel system of human endometrium

C. Isaac, J. W. Pollard, U. T. Meier

Research output: Contribution to journalArticlepeer-review

52 Scopus citations


Exogenous expression of the characteristic repeat domain of the nucleolar chaperone Nopp140 induces the formation of intranuclear structures, termed R-rings. Here, the R-rings are identified as extensive stacks of membrane cisternae in the otherwise membrane-free nucleus. They consist of bona fide endoplasmic reticulum (ER) containing integral membrane proteins of the smooth and rough ER. Although lacking nuclear pore complexes and lamina, the R-rings derive specifically from the inner nuclear membrane. These findings are consistent with the idea that all transmembrane proteins synthesized in the ER and the outer nuclear membrane can freely diffuse through the pore membrane domain into the inner membrane. Uniquely, the soluble transfected Nopp140 is directly involved in the generation of these membrane stacks as it localizes to the electron dense matrix in which they are embedded. The only well-documented example of intranuclear membrane proliferation is the nucleolar channel system of the postovulation human endometrium. The transient emergence of the nucleolar channel system correlates precisely with the readiness of the endometrium for the implantation of the fertilized egg. The nucleolar channel system exhibits an ultrastructure that is indistinguishable from R-rings, and nuclei of human endometrium harbor Nopp140 and ER marker containing structures. Therefore, the nucleolar channel system appears to be identical to the R-rings, suggesting a role for Nopp140 in human reproduction.

Original languageEnglish (US)
Pages (from-to)4253-4264
Number of pages12
JournalJournal of cell science
Issue number23
StatePublished - Dec 27 2001


  • Endoplasmic reticulum
  • Human endometrium
  • Nopp140
  • Nucleolar channel system
  • Nucleolus

ASJC Scopus subject areas

  • Cell Biology


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