The mycelium of Aspergillus nidulans is composed of multinucleate cellular compartments delimited by crosswalls called septa. Septum formation is dependent on mitosis and requires the recruitment of actin to the site of septum formation. Employing a collection of temperature sensitive nuclear distribution (nudA2, nudC3 and nudF7), nuclear division (nimA5, hfaB3), and septation (sepD5, sepG1) mutants, we have investigated the interdependency among nuclear positioning, mitosis, and cell growth in structuring the cellular compartments of A. nidulans. The cellular compartments of nud+ strains were highly uniform with regard to nuclear distribution and averaged 38 microns in length. Incubation of nud mutants at semi-restrictive temperature resulted in aberrant nuclear distribution that appeared to direct the formation of variable-sized cellular compartments, ranging from 5 microns to greater than 81 microns. In germinating spores, the first septum forms at the basal end of the germ tube following the third round of nuclear division. Germlings must undergo mitosis in order to form a septum. Temperature-sensitive mitotic mutants were used to show that a single nuclear division is sufficient to activate septum formation, provided a critical cell size has been attained. In mitotic mutants and wild-type cells, delays in nuclear division resulted in the misplacement of the first septum. These results strongly support the role of mitotic nuclei in determining septal placement, and suggest that cell size control is post-mitotic in A. nidulans.

REFERENCES

Beckwith
S. M.
,
Roghi
C. H.
,
Morris
N. R.
(
1995
).
The genetics of nuclear migration in fungi.
Genet. Eng
17
,
165
180
Chang
F.
,
Nurse
P.
(
1996
).
How fission yeast fission in the middle.
Cell
84
,
191
194
Chang
F.
,
Wollard
A.
,
Nurse
P.
(
1996
).
Isolation and characterization of fission yeast mutants defective in the assembly and placement of the contractile actin ring.
J. Cell Sci
109
,
131
142
Chant
J.
,
Pringle
J. R.
(
1991
).
Budding and cell polarity in Saccharomyces cerevisiae.
Curr. Opin. Gen. Dev
1
,
342
350
Clutterbuck
A. J.
(
1969
).
Cell volume per nucleus in haploid and diploid strains of Aspergillus nidulans.
J. Gen. Microbiol
55
,
291
299
Clutterbuck
A. J.
(
1970
).
Synchronous nuclear division and septation in Aspergillus nidulans.
J. Gen. Microbiol
60
,
133
135
Clutterbuck
A. J.
(
1994
).
Mutants of Aspergillus nidulans deficient in nuclear migration during hyphal growth and conidiation.
Microbiology
140
,
1169
1174
Doonan
J. H.
(
1992
).
Cell division in Aspergillus.
J. Cell Sci
103
,
599
611
Fankhauser
C.
,
Marks
J.
,
Reymond
A.
,
Simanis
V.
(
1993
).
The S. pombecdc16 gene is required both for the maintenance of p34cdc2kinase activity and the regulation of septum formation: a link between mitosis and cytokinesis?.
EMBO J
12
,
2697
2704
Featherstone
C.
,
Russell
P.
(
1991
).
Fission yeast p107wee1 mitotic inhibitor is a tyrosine/serine kinase.
Nature
349
,
808
811
Fiddy
C.
,
Trinci
A. P. J.
(
1976
).
Morphology and growth of a temperature-sensitive mutant of Aspergillus nidulans which forms aseptate mycelia at non-permissive temperatures.
J. Gen. Microbiol
11
,
53
59
Fischer
R.
,
Timberlake
W. E.
(
1995
).
Aspergillus nidulansapsA (anucleate primary sterigmata) encodes a coiled-coil protein required for nuclear positioning and completion of asexual development.
J. Cell Biol
128
,
485
498
Girbardt
M.
(
1979
).
A microfilamentous septal belt (FSB) during induction of cytokinesis in Trametes versicolor (L. ex Fr.).
Exp. Mycol
3
,
215
228
Harris
S. D.
,
Morrell
J. L.
,
Hamer
J. E.
(
1994
).
Identification and characterization of Aspergillus nidulans mutants defective in cytokinesis.
Genetics
136
,
517
532
Hirano
T.
,
Funahashi
S.
,
Uemura
T.
,
Yanagida
M.
(
1986
).
Isolation and characterization of Schizosaccharomyces pombecut mutants that block nuclear division but not cytokinesis.
EMBO J
5
,
2973
2979
Jackson
S. L.
,
Heath
I. B.
(
1993
).
Roles of calcium ions in hyphal tip growth.
Microbiol. Rev.
57
,
367
382
Johnston
G. C.
,
Pringle
J. R.
,
Hartwell
L. H.
(
1977
).
Coordination of growth with cell division in the yeast Saccharomyces cerevisiae.
Exp. Cell Res
105
,
79
98
Kafer
E.
(
1977
).
Meiotic and mitotic recombination in Aspergillus and its chromosomal aberrations.
Advan. Genet
19
,
33
131
Katz
D.
,
Rosenberger
R. F.
(
1971
).
Hyphal wall synthesis in Aspergillus nidulans: Effect of protein synthesis inhibition and osmotic shock on chitin insertion and morphogenesis.
J. Bacteriol
108
,
184
190
Li
Y. Y.
,
Yeh
E.
,
Hays
T.
,
Bloom
K.
(
1993
).
Disruption of mitotic spindle orientation in a yeast dynein mutant.
Proc. Nat. Acad. Sci. USA
90
,
10096
100
Lundgren
K.
,
Walworth
N.
,
Booher
R.
,
Dembski
M.
,
Kirschner
M.
,
Beach
D.
(
1991
).
mik1 and wee1 cooperate in the inhibitory tyrosine phosphorylation of cdc2.
Cell
64
,
1111
1122
Momany
M.
,
Morrell
J. L.
,
Harris
S. D.
,
Hamer
J. E.
(
1995
).
Septum formation in Aspergillus nidulans.
Can. J. Bot
73
,
396
–.
Nurse
P.
(
1975
).
Genetic control of cell size at cell division in yeast.
Nature
256
,
547
551
Osmani
A. H.
,
Osmani
S. A.
,
Morris
N. R.
(
1990
).
The molecular cloning and identification of a gene product specifically required for nuclear movement in Aspergillus nidulans.
J. Cell Biol
111
,
543
551
Osmani
A. H.
,
McGuire
S. L.
,
Osmani
S. A.
(
1991
).
Parallel activation of the NIMA and p34cdc2cell cycle-regulated protein kinases is required to initiate mitosis in A. nidulans.
Cell
67
,
283
291
Osmani
A.
,
Noel
P.
,
Mischke
M.
(
1994
).
A single p34cdc2protein kinase(encoded by nimX cdc2) is required at G1and G2in Aspergillus nidulans.
J. Cell Sci
107
,
1519
28
Osmani
S. A.
,
May
G. S.
,
Morris
N. R.
(
1987
).
Regulation of the mRNA levels of nimA, a gene required for the G2-M transition in Aspergillus nidulans.
J. Cell Biol
104
,
1495
504
Palmer
R. E.
,
Sullivan
D. S.
,
Huffaker
T.
,
Koshland
D.
(
1992
).
Role of astral microtubules and actin in spindle orientation and migration in the budding yeast, Saccharomyces cerevisiae.
J. Cell Biol
119
,
583
593
Parker
L. L.
,
Atherton-Fessler
S.
,
Lee
M. S.
,
Ogg
S.
,
Falk
J. L.
,
Swenson
K.
,
Piwnica-Worms
H.
(
1991
).
Cyclin promotes the tyrosine phosphorylation of p34 cdc2 in a wee1 +dependent manner.
EMBO J
10
,
1255
1263
Parker
L. L.
,
Atherton-Fessler
S.
,
Piwnica-Worms
H.
(
1992
).
p107wee1 is a dual-specificity kinase that phosphorylates p34 cdc2 on tyrosine 15.
Proc. Nat. Acad. Sci. USA
89
,
2917
2921
Rosenberger
R. F.
,
Kessel
M.
(
1967
).
Synchrony of nuclear replication in individual hyphae of Aspergillus nidulans.
J. Bacteriol
94
,
1464
1469
Russell
P.
,
Nurse
P.
(
1987
).
Negative regulation of mitosis by wee1 +, a gene encoding a protein kinase homolog.
Cell
49
,
559
67
Samejima
I.
,
Matsumoto
M.
,
Nakaseko
Y.
,
Beach
D.
,
Yanagida
M.
(
1993
).
Identification of seven new cut genes involved in Schizosaccharomyces pombe mitosis.
J. Cell Sci
105
,
135
143
Simanis
V.
(
1995
).
The control of septum formation and cytokinesis in fission yeast.
Semin. Cell Biol
6
,
79
87
Strome
S.
(
1993
).
Determination of cleavage planes.
Cell
72
,
3
6
Trinci
A. P. J.
,
Morris
N. R.
(
1979
).
Morphology and growth of a temperature-sensitive mutant of Aspergillus nidulans which forms aseptate mycelia at non-permissive temperatures.
J. Gen. Microbiol
114
,
53
59
Upshall
A.
,
Mortimore
I. D.
(
1984
).
Isolation of aneuploid generating mutants of Aspergillus nidulans, one of which is defective in interphase of the cell cycle.
Genetics
108
,
107
121
Xiang
X.
,
Osmani
A. H.
,
Osmani
S. A.
,
Xin
M.
,
Morris
N. R.
(
1995
).
NudF, a nuclear migration gene in Aspergillus nidulans, is similar to the human LIS-1 gene required for neuronal migration.
Mol. Biol. Cell
6
,
297
310
Xiang
X.
,
Roghi
C.
,
Morris
N. R.
(
1995
).
Characterization and localization of the cytoplasmic dynein heavy chain in Aspergillus nidulans.
Proc. Nat. Acad. Sci. USA
92
,
9890
9894
Yeh
E.
,
Skibbens
R. V.
,
Cheng
J. W.
,
Salmon
E. D.
,
Bloom
K.
(
1995
).
Spindle dynamics and cell cycle regulation of dynein in the budding yeast, Saccharomycescerevisiae.
J. Cell Biol
130
,
687
700
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