title: Cytoplasmic bulk flow propels nuclei in mature hyphae of Neurospora crassa.
abstract: We used confocal microscopy to evaluate nuclear dynamics in mature, growing hyphae of Neurospora crassa whose nuclei expressed histone H1-tagged green fluorescent protein (GFP). In addition to the H1-GFP wild-type (WT) strain, we examined nuclear displacement (passive transport) in four mutants deficient in microtubule-related motor proteins (ro-1, ro-3, kin-1, and a ro-1 kin-1 double mutant). We also treated the WT strain with benomyl and cytochalasin A to disrupt microtubules and actin microfilaments, respectively. We found that the degree of nuclear displacement in the subapical regions of all strains correlated with hyphal elongation rate. The WT strain and that the ro-1 kin-1 double mutant showed the highest correlation between nuclear movement and hyphal elongation. Although most nuclei seemed to move forward passively, presumably carried by the cytoplasmic bulk flow, a small proportion of the movement detected was either retrograde or accelerated anterograde. The absence of a specific microtubule motor in the mutants ro-1, ro-3, or kin-1 did not prevent the anterograde and retrograde migration of nuclei; however, in the ro-1 kin-1 double mutant retrograde migration was absent. In the WT strain, almost all nuclei were elongated, whereas in all other strains a majority of nuclei were nearly spherical. With only one exception, a sizable exclusion zone was maintained between the apex and the leading nucleus. The ro-1 mutant showed the largest nucleus exclusion zone; only the treatment with cytochalasin A abolished the exclusion zone. In conclusion, the movement and distribution of nuclei in mature hyphae appear to be determined by a combination of forces, with cytoplasmic bulk flow being a major determinant. Motor proteins probably play an active role in powering the retrograde or accelerated anterograde migrations of nuclei and may also contribute to passive anterograde displacement by binding nuclei to microtubules.
authors.affiliation: Departamento de Microbiología, División de Biología Experimental y Aplicada, Centro de Investigación Científica y Educación Superior de Ensenada, Km 107, Carretera Tijuana Ensenada, Ensenada, Mexico.
authors.forename: Silvia L
authors.initials: SL
authors.lastname: Ramos-García
authors.forename: Robert W
authors.initials: RW
authors.lastname: Roberson
authors.forename: Michael
authors.initials: M
authors.lastname: Freitag
authors.forename: Salomón
authors.initials: S
authors.lastname: Bartnicki-García
authors.forename: Rosa R
authors.initials: RR
authors.lastname: Mouriño-Pérez
mesh_terms: D002467:Cell Nucleus / Q000378:metabolism*; D036681:Fluorescence Recovery After Photobleaching; D049452:Green Fluorescent Proteins / Q000378:metabolism; D025301:Hyphae / Q000166:cytology* / Q000254:growth & development / Q000378:metabolism*; D007399:Interphase; D022101:Microtubule-Organizing Center / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism; D008954:Models, Biological; D009068:Movement; D009492:Neurospora crassa / Q000166:cytology* / Q000254:growth & development / Q000378:metabolism*; D012044:Regression Analysis
chemical_list: D049452:Green Fluorescent Proteins
references.citation: Curr Genet. 1999 Jul;35(6):626-30
references.pmid: 10467007
references.citation: Mol Biol Cell. 1998 Jul;9(7):1627-31
references.pmid: 9658159
references.citation: J Cell Sci. 2002 Apr 1;115(Pt 7):1453-60
references.pmid: 11896193
references.citation: J Cell Sci. 2003 Nov 15;116(Pt 22):4501-12
references.pmid: 14576344
references.citation: J Cell Biol. 1994 Oct;127(1):139-149
references.pmid: 7929559
references.citation: Fungal Genet Biol. 2000 Dec;31(3):233-44
references.pmid: 11273684
references.citation: Fungal Genet Biol. 2006 Jun;43(6):389-400
references.pmid: 16621627
references.citation: J Cell Biol. 1992 Jul;118(2):385-95
references.pmid: 1378448
references.citation: J Cell Sci. 1998 Jun;111 ( Pt 11):1555-66
references.pmid: 9580563
references.citation: EMBO J. 1997 Jun 2;16(11):3025-34
references.pmid: 9214620
references.citation: J Cell Sci. 2001 Mar;114(Pt 5):975-86
references.pmid: 11181180
references.citation: Mol Microbiol. 1999 Jun;32(5):1065-76
references.pmid: 10361308
references.citation: Fungal Genet Biol. 2007 Jul;44(7):672-81
references.pmid: 17329132
references.citation: J Cell Biol. 1998 Nov 30;143(5):1239-47
references.pmid: 9832552
references.citation: Eukaryot Cell. 2003 Apr;2(2):341-50
references.pmid: 12684383
references.citation: Res Microbiol. 2000 May;151(4):247-54
references.pmid: 10875281
references.citation: Fungal Genet Biol. 2004 Oct;41(10):897-910
references.pmid: 15341912
references.citation: Mol Microbiol. 1997 Aug;25(4):757-69
references.pmid: 9379904
references.citation: Protoplasma. 1977;92(3-4):195-210
references.pmid: 910080
references.citation: J Cell Biol. 1995 Feb;128(4):485-98
references.pmid: 7860626
references.citation: Mol Microbiol. 2001 Oct;42(1):121-32
references.pmid: 11679072
references.citation: Proc Natl Acad Sci U S A. 1994 Mar 15;91(6):2100-4
references.pmid: 8134356
references.citation: Fungal Genet Biol. 2004 Feb;41(2):213-25
references.pmid: 14732267
references.citation: Microbiology (Reading). 2005 Aug;151(Pt 8):2685-2692
references.pmid: 16079346
references.citation: J Cell Biol. 2000 Mar 20;148(6):1097-101
references.pmid: 10725321
references.citation: Biophys J. 2000 Nov;79(5):2382-90
references.pmid: 11053117
references.citation: Genet Res. 1975 Dec;26(3):237-54
references.pmid: 773766
references.citation: Proc Natl Acad Sci U S A. 1994 Dec 6;91(25):12228-32
references.pmid: 7991610
references.citation: Development. 2001 Dec;128(24):5039-50
references.pmid: 11748140