The JNM1 gene in the yeast Saccharomyces cerevisiae is required for nuclear migration and spindle orientation during the mitotic cell cycle.

Abstract

Abstract. JNM1, a novel gene on chromosome XIII in the yeast Saccharomyces cerevisiae, is required for proper nuclear migration, jnml null mutants have a temperature-dependent defect in nuclear migration and an accompanying alteration in astral microtubules. At 30°C, a significant proportion of the mitotic spindles is not properly located at the neck between the mother cell and the bud. This defect is more severe at low temperature. At ll°C, 60% of the cells accumulate with large buds, most of which have two DAPI staining regions in the mother cell. Although mitosis is delayed and nuclear migration is defective in jnml mutants, we rarely observe more than two nuclei in a cell, nor do we frequently observe anuclear cells. No loss of viability is observed at ll°C and cells continue to grow exponentially with increased doubling time. T HE nuclei in the budding yeast Saccharomyces cerevisiae migrate to the neck between the mother cell and the bud prior to mitosis and the spindle microtubules orient along the long axis of the cell. At mitosis the spindle elongates through the neck between the mother cell and the bud and chromosomes separate, depositing one set of chromosomes in the mother cell body and one set in the bud. A key role for microtubules in this process has been shown by the inhibitory effects on nuclear migration by microtubule inhibitors (Jacobs et al., 1988) and by defects in nuclear migration exhibited by some B tubulin mutants (Huffaker et al., 1988). Cytoplasmic (or astral) microtubules appear to be mainly responsible for nuclear migration.Mutant alleles of the tub2 gene that impart a specific defect in astral microtubule stability show defects in nuclear migration during mitosis or karyogamy, but have relatively little

The Centrosome and Its Duplication Cycle

“…In one, Kar9 associates with both the microtubule plus end-binding protein EB1 and the myosin motor protein Myo2 to guide astral microtubules along actin filaments that emanate from the incipient bud site and growing bud tips (Beach et al 2000;Lee et al 2000;Yin et al 2000). In the second pathway, dynein both guides the astral microtubules along the cell cortex and promotes instability of the plus ends to ensure end-on association of microtubules with the cortex (McMillan and Tatchell 1994;Carminati and Stearns 1997;Adames and Cooper 2000;Heil-Chapdelaine et al 2000;Yeh et al 2000). When astral guidance fails, the ensuing nuclear division within the mother cell blocks cytokinesis and mitotic exit through activation of the spindle orientation checkpoint (SPOC) (Yeh et al 1995;Bardin et al 2000;Pereira et al 2000;Caydasi and Pereira 2012).…”

Interdependence of Filamentous Actin and Microtubules for Asymmetric Cell Division

“…Mutations in both the dynactin complex (Li et al, 1993;McMillan and Tatchell, 1994;Muhua et al, 1994;Clark and Meyer, 1994) and in two proteins, Num1p (Farkasovsky and Küntzel, 1995) and Karp9 (Miller and Rose, 1998), were found to result in defects in spindle positioning and orientation.…”

“…Elimination of other proteins, which are now known to be part of the dynactin complex, resulted in identical phenotypes. Deletion of either the actin-related protein Arp1 (Muhua et al, 1994;Clark and Meyer, 1994) or Jnm1p (McMillan and Tatchell, 1994) led to a failure to properly position and orient the mitotic spindle. As for dyn1⌬ mutants, astral microtubules are abundant and extend into the bud curving along the cortex (McMillan and Tatchell, 1994).…”

“…Deletion of either the actin-related protein Arp1 (Muhua et al, 1994;Clark and Meyer, 1994) or Jnm1p (McMillan and Tatchell, 1994) led to a failure to properly position and orient the mitotic spindle. As for dyn1⌬ mutants, astral microtubules are abundant and extend into the bud curving along the cortex (McMillan and Tatchell, 1994). The phenotypes described for the mutants are consistent with dynactin mediating an interaction between astral microtubules and the cell cortex.…”

A gene required for nuclear migration in Neurospora crassa codes for a protein with cysteine‐rich, LIM/RING‐like domains

“…Two other yeast genes, encoding proteins which function specifically in nuclear migration, have also been described. The NUM1 gene encodes a predicted 313 kDa protein which contains 12 nearly perfect repeats of a 64 amino acid sequence (Kormanec et al, 1991) and the JNM1 gene, a 43.6 kDa protein with three predicted coiled-coil domains (McMillan and Tatchell, 1994). However, the precise functions of either of the NUM1 or JNM1 products are presently unknown.…”