Intranuclear sphingomyelin is associated with transcriptionally active chromatin and plays a role in nuclear integrity.
BACKGROUND
Sphingomyelin is one of the major phospholipids in the cell nucleus. However, its intranuclear distribution with regard to different functional nuclear domains as well as its possible involvement in the nuclear functional architecture remains to be elucidated.


RESULTS
We carried out an ultrastructural cytochemical study of the intranuclear distribution of SM (sphingomyelin) using an in situ binding assay of neutral SMase (sphingomyelinase) conjugated to colloidal gold particles. The enzymatic labelling was carried out on ultrathin sections of different mammalian cells prepared by means of various fixation and resin-embedding protocols. Transmission electron microscopic analysis revealed preferential localization of SM within the PR (perichromatin region), a functionally important nucleoplasmic domain containing sites of pre-mRNA synthesis and processing. In the nucleolus, SM is mostly associated with the dense fibrillar component containing transcriptionally active ribosomal genes. Microinjection of enzymatically active SMase into living cells resulted in a rapid degradation of intranuclear structure.


CONCLUSIONS
Our observations, supported by biochemical data, provide evidence for the involvement of SM in important nuclear functions. They bring additional information pointing out the PR as an essential functional nuclear domain. Furthermore, they suggest a role for SM in the internal nuclear architecture.
Scassellati
Catia
C
Centre of Electron Microscopy, University of Lausanne, Bugnon 27, CH-1005 Lausanne, Switzerland.
Albi
Elisabetta
E
Cmarko
Dusan
D
Tiberi
Cinzia
C
Cmarkova
Jana
J
Bouchet-Marquis
Cedric
C
Verschure
Pernette J
PJ
Driel
Roel van
Rv
Magni
Mariapia Viola
MV
Fakan
Stanislav
S
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism* / Q000648:ultrastructure*; D002843:Chromatin / Q000378:metabolism* / Q000648:ultrastructure*; D051379:Mice; D046529:Microscopy, Electron, Transmission; D051381:Rats; D013109:Sphingomyelins / Q000378:metabolism*; D014158:Transcription, Genetic
D002843:Chromatin; D013109:Sphingomyelins