title: The nucleolar channel system of human endometrium is related to endoplasmic reticulum and R-rings.
abstract: The nucleolar channel system (NCS) is a well-established ultrastructural hallmark of the postovulation endometrium. Its transient presence has been associated with human fertility. Nevertheless, the biogenesis, composition, and function of these intranuclear membrane cisternae are unknown. Membrane systems with a striking ultrastructural resemblance to the NCS, termed R-rings, are induced in nuclei of tissue culture cells by overexpression of the central repeat domain of the nucleolar protein Nopp140. Here we provide a first molecular characterization of the NCS and compare the biogenesis of these two enigmatic organelles. Like the R-rings, the NCS consists of endoplasmic reticulum harboring the marker glucose-6-phosphatase. R-ring formation initiates at the nuclear envelope, apparently by a calcium-mediated Nopp140-membrane interaction, as supported by the calcium-binding ability of Nopp140, the inhibition of R-ring formation by calcium chelators, and the concentration of Nopp140 and complexed calcium in R-rings. Although biogenesis of the NCS may initiate similarly, the reduced presence of complexed calcium and Nopp140 suggests the involvement of additional factors.
authors.affiliation: Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Nupur
authors.initials: N
authors.lastname: Kittur
authors.forename: Gregory
authors.initials: G
authors.lastname: Zapantis
authors.forename: Mira
authors.initials: M
authors.lastname: Aubuchon
authors.forename: Nanette
authors.initials: N
authors.lastname: Santoro
authors.forename: David P
authors.initials: DP
authors.lastname: Bazett-Jones
authors.forename: U Thomas
authors.initials: UT
authors.lastname: Meier
mesh_terms: D002118:Calcium / Q000378:metabolism; D002466:Cell Nucleolus / Q000378:metabolism* / Q000648:ultrastructure; D004717:Endometrium / Q000166:cytology*; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000648:ultrastructure; D005260:Female; D006801:Humans; D016253:Microscopy, Immunoelectron; D009687:Nuclear Proteins / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism
chemical_list: C075564:NOLC1 protein, human; D009687:Nuclear Proteins; D010750:Phosphoproteins; D002118:Calcium