Dynactin and Num1 cooperate to establish the cortical anchoring of cytoplasmic dynein inS. pombe

Abstract

Chromosome movement during meiosis is crucial for homologous pairing and meiotic recombination. During meiotic prophase in fission yeast, rapid nuclear migration is dependent on cytoplasmic dynein, which is anchored to the cell cortex and pulls microtubules, thereby driving nuclear migration. However, the precise mechanisms underlying dynein localization and activation remain unclear. Here, we identified three subunits of dynactin in fission yeast: Arp1, Mug5 and Jnm1 (also known as Mug1). These subunits transiently colocalized with dynein foci at the cell cortex and were essential for the cortical anchoring of dynein. Cortical factor Num1 (also known as Mcp5), which was also required for dynein anchoring, bound to dynein independently of dynactin. Whereas Num1 suppressed the sliding of dynein foci along the cortex, Arp1, Mug5 and Jnm1 were involved in the regulation of shrinkage and bundling of microtubules. From these data, we propose that dynein anchoring is established by cooperation of transient assembly of dynactin and function of Num1 at the cell cortex.

A systematic screen for morphological abnormalities during fission yeast sexual reproduction identifies a mechanism of actin aster formation for cell fusion

“…All 8 strains were verified by PCR for correct deletion of the corresponding gene. The others include the actin capping protein Acp2, previously involved in actin cytoskeleton organization during mitotic growth [33,34], the centractin family actin like protein Arp1, part of the dynactin complex previously implicated in dynein-dependent nuclear movement during meiotic prophase (horsetail movement; [35]), the actin monomer-binding protein twinfilin twf1 involved in regulation of polarized growth [36], and the BAR-domain protein Hob3, which was previously known to regulate cytokinesis in part through regulation of Cdc42 GTPase [37]. A recently described regulator of the type V myosin Myo51, Rng8, was also selected [21].…”

Fission yeast myosin I facilitates PI(4,5)P 2 -mediated anchoring of cytoplasmic dynein to the cortex

“…The key players required for the movement of the nucleus are (i) the minus-end-directed motor protein cytoplasmic dynein, which is the force generator (2, 5); (ii) the anchor protein of dynein at the cortex, meiotic coiled-coil (CC) protein 5 (Mcp5), which acts as a link between dynein and the cell membrane (6,7); and (iii) the microtubule cytoskeleton, which transduces the force produced by dynein to the spindle pole body (SPB, centrosome in yeast) and thereby to the nucleus underlying it (1). In fission yeast, cells lacking either dynein or Mcp5 are viable in interphase but do not exhibit oscillations during meiosis and thus show defects in sporulation (2,(6)(7)(8).…”

Activation of the motor protein upon attachment: Anchors weigh in on cytoplasmic dynein regulation

“…In S. pombe , the Lis1 homolog is yet to be discovered, and it remains unclear whether a similar mechanism operates in dynein activation. The dynein IC (Dic1) co‐localised with the HC in fluorescence microscopy , and immunoprecipitated with Mcp5 independent of dynactin . This likely indicates an interaction between the dynein complex and Mcp5 mediated by IC, similar to that found in the budding yeast system .…”

“…This finding lead to the conclusion that binding of dynein to the anchor Mcp5 relieved the inhibition of dynein's motor activity and enabled it to move in a minus‐end‐directed fashion. In recent work, it was suggested that this activation upon anchoring also involves assembly of dynactin subunits Mug5 (p24), Jnm1 (p50) and Arp1 based on accumulation of dynein at the plus‐end of microtubules in mutants of the dynactin subunits , similar to what was observed in budding yeast . More experiments with mutants of the dynein motor will be required to identify the minimal dynein complex required for processive directed movement.…”

“…This likely indicates an interaction between the dynein complex and Mcp5 mediated by IC, similar to that found in the budding yeast system . Interestingly, the anchoring of dynein to Mcp5 was not observed in strains expressing dynein HC mutated in its first AAA+ domain, suggesting that active dynein is required for its anchoring . This unbinding of the mutated dynein was proposed to occur due to high load forces exerted upon anchored mutated dynein by the shrinking of microtubules .…”