title: Mouse nuclear myosin I knock-out shows interchangeability and redundancy of myosin isoforms in the cell nucleus.
abstract: BACKGROUND
  Nuclear myosin I (NM1) is a nuclear isoform of the well-known "cytoplasmic" Myosin 1c protein (Myo1c). Located on the 11(th) chromosome in mice, NM1 results from an alternative start of transcription of the Myo1c gene adding an extra 16 amino acids at the N-terminus. Previous studies revealed its roles in RNA Polymerase I and RNA Polymerase II transcription, chromatin remodeling, and chromosomal movements. Its nuclear localization signal is localized in the middle of the molecule and therefore directs both Myosin 1c isoforms to the nucleus.
  
  
  RESULTS
  In order to trace specific functions of the NM1 isoform, we generated mice lacking the NM1 start codon without affecting the cytoplasmic Myo1c protein. Mutant mice were analyzed in a comprehensive phenotypic screen in cooperation with the German Mouse Clinic. Strikingly, no obvious phenotype related to previously described functions has been observed. However, we found minor changes in bone mineral density and the number and size of red blood cells in knock-out mice, which are most probably not related to previously described functions of NM1 in the nucleus. In Myo1c/NM1 depleted U2OS cells, the level of Pol I transcription was restored by overexpression of shRNA-resistant mouse Myo1c. Moreover, we found Myo1c interacting with Pol II. The ratio between Myo1c and NM1 proteins were similar in the nucleus and deletion of NM1 did not cause any compensatory overexpression of Myo1c protein.
  
  
  CONCLUSIONS
  We observed that Myo1c can replace NM1 in its nuclear functions. Amount of both proteins is nearly equal and NM1 knock-out does not cause any compensatory overexpression of Myo1c. We therefore suggest that both isoforms can substitute each other in nuclear processes.
authors.affiliation: Department of Biology of Cell Nucleus, Institute of Molecular Genetics, ASCR, v.v.i., Prague, Czech Republic.
authors.forename: Tomáš
authors.initials: T
authors.lastname: Venit
authors.forename: Rastislav
authors.initials: R
authors.lastname: Dzijak
authors.forename: Alžběta
authors.initials: A
authors.lastname: Kalendová
authors.forename: Michal
authors.initials: M
authors.lastname: Kahle
authors.forename: Jana
authors.initials: J
authors.lastname: Rohožková
authors.forename: Volker
authors.initials: V
authors.lastname: Schmidt
authors.forename: Thomas
authors.initials: T
authors.lastname: Rülicke
authors.forename: Birgit
authors.initials: B
authors.lastname: Rathkolb
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Hans
authors.forename: Alexander
authors.initials: A
authors.lastname: Bohla
authors.forename: Oliver
authors.initials: O
authors.lastname: Eickelberg
authors.forename: Tobias
authors.initials: T
authors.lastname: Stoeger
authors.forename: Eckhard
authors.initials: E
authors.lastname: Wolf
authors.forename: Ali Önder
authors.initials: AÖ
authors.lastname: Yildirim
authors.forename: Valérie
authors.initials: V
authors.lastname: Gailus-Durner
authors.forename: Helmut
authors.initials: H
authors.lastname: Fuchs
authors.forename: Martin Hrabě
authors.initials: MH
authors.lastname: de Angelis
authors.forename: Pavel
authors.initials: P
authors.lastname: Hozák
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002467:Cell Nucleus / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D005838:Genotype; D047468:Immunoprecipitation; D051379:Mice; D018345:Mice, Knockout; D024461:Myosin Type I / Q000235:genetics* / Q000378:metabolism*; D010641:Phenotype; D010957:Plasmids / Q000235:genetics; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D017931:DNA Primers; C470422:Myo1c protein, mouse; D020033:Protein Isoforms; D024461:Myosin Type I