The centrosome is the major microtubule organizing centre (MTOC) in animal cells. The canonical centrosome is composed of two centrioles surrounded by a pericentriolar matrix (PCM). In contrast, yeasts and amoebozoa have lost centrioles and possess acentriolar centrosomes—called the spindle pole body (SPB) and the nucleus-associated body (NAB), respectively. Despite the difference in their structures, centriolar centrosomes and SPBs not only share components but also common biogenesis regulators. In this review, we focus on the SPB and speculate how its structures evolved from the ancestral centrosome. Phylogenetic distribution of molecular components suggests that yeasts gained specific SPB components upon loss of centrioles but maintained PCM components associated with the structure. It is possible that the PCM structure remained even after centrosome remodelling due to its indispensable function to nucleate microtubules. We propose that the yeast SPB has been formed by a step-wise process; (1) an SPB-like precursor structure appeared on the ancestral centriolar centrosome; (2) it interacted with the PCM and the nuclear envelope; and (3) it replaced the roles of centrioles. Acentriolar centrosomes should continue to be a great model to understand how centrosomes evolved and how centrosome biogenesis is regulated.

The spindle checkpoint delays the onset of anaphase until all of the chromosomes properly achieve bipolar attachment to the spindle. It has been shown that unattached kinetochores are the site that emits a signal for activation of the checkpoint. Although the components of the checkpoint such as Bub1, Mad1 and Mad2 selectively accumulate at unattached kinetochores, the answer to how they recognize unattached kinetochores has remained elusive. Mps1 pombe homolog (Mph1) kinase has been shown to function upstream of most of the components of the checkpoint and thus it is thought to recognize unattached kinetochores by itself and recruit other components. In this study we have expressed a fusion protein of Mph1 and Ndc80 (a kinetochore protein of the outer plate) and shown that the fusion protein arrests cell cycle progression in a spindle-checkpoint\x{2013}dependent manner in fission yeast. When expression of Mad2 is turned off, the cells grow normally with Mph1 constitutively localized at centromeres/kinetochores. Under this condition, Bub1 can be found with Mph1 throughout the cell cycle, indicating that localization of Mph1 at centromeres/kinetochores is sufficient to recruit Bub1. In contrast, Mad1 is found to transiently localize at kinetochores, which are presumably unattached to the spindle, but soon it dissociates from kinetochores. We propose that Mph1 is a sufficient marker for recruitment of Bub1. Mad1, in contrast, requires an additional condition/component for stable association with kinetochores.

The centrosome is composed of two centrioles surrounded by a microtubule-nucleating pericentriolar material (PCM). Although centrioles are known to regulate PCM assembly, it is less known whether and how the PCM contributes to centriole assembly. Here we investigate the interaction between centriole components and the PCM by taking advantage of fission yeast, which has a centriole-free, PCM-containing centrosome, the SPB. Surprisingly, we observed that several ectopically-expressed animal centriole components such as SAS-6 are recruited to the SPB. We revealed that a conserved PCM component, Pcp1/pericentrin, interacts with and recruits SAS-6. This interaction is conserved and important for centriole assembly, particularly its elongation. We further explored how yeasts kept this interaction even after centriole loss and showed that the conserved calmodulin-binding region of Pcp1/pericentrin is critical for SAS-6 interaction. Our work suggests that the PCM not only recruits and concentrates microtubule-nucleators, but also the centriole assembly machinery, promoting biogenesis close by.

Band 3 deficiency with hereditary spherocytosis and hemolytic anemia in Japanese black cattle, band 3^Bov.Yamagata, is caused by a total lack of band 3 protein with an autosomal dominant inheritance. Genotyping for band 3 deficiency and sexing were successfully achieved in biopsied embryo cells with efficiencies of 98.4% and 97.4%, respectively. Transfer of the embryo that was determined as homozygous for the mutant allele into a recipient cow resulted in the production of a fetus exhibiting the genotype and red cell phenotypes characteristic of band 3^Bov.Yamagata. These results demonstrate that our procedure is reliable and applicable to produce animals free from or homozygous for the mutant allele by breeding carrier animals.