Momany Michelle, Taylor Ian
Department of Botany, University of Georgia, Athens, GA 30602 7271, USA1.
Microbiology (Reading). 2000 Dec;146 Pt 12:3279-3284. doi: 10.1099/00221287-146-12-3279.
When the spores of filamentous fungi break dormancy, nuclear division is accompanied by a series of ordered morphological events including the switch from isotropic to polar growth, the emergence of a second germ tube from the conidium and septation. Correlation of these morphological events with nuclear number allows them to serve as duplication cycle landmarks. Early duplication cycle landmarks have been characterized in Aspergillus nidulans, but not in other filamentous fungi. To learn more about duplication cycle control in filamentous fungi, a study was undertaken to compare the timing of landmarks in Aspergillus fumigatus and A. nidulans. Nuclear duplication took approximately 45 min in A. fumigatus, with mitosis occupying roughly 5% of this period. Under the same conditions, nuclear duplication in A. nidulans took approximately 60 min, with mitosis occupying roughly 4% of this period. In A. fumigatus the isotropic to polar switch preceded the first mitosis in 22% of cells, while in A. nidulans the isotropic to polar switch did not occur until after the first mitosis. In both A. fumigatus and A. nidulans the earliest emergence of a second germ tube from the conidium occurred after the third mitotic division. However, by the fifth mitosis only 19% of A. fumigatus conidia had a second germ tube, compared to 98% of A. nidulans conidia. In both A. fumigatus and A. nidulans, formation of the first septum occurred after the fourth mitotic division. In all experiments a few cells lagged behind the others in nuclear number. In this delayed group, it was common to see landmark events at an earlier mitotic division. Differences in nuclear number when identical landmarks occur in A. fumigatus versus A. nidulans, and uncoupling of mitotic division and landmarks in delayed cells suggest that nuclear division and morphogenesis lie in parallel pathways, perhaps coordinated by checkpoints.
当丝状真菌的孢子打破休眠时，核分裂伴随着一系列有序的形态学事件，包括从各向同性生长向极性生长的转变、分生孢子中第二个芽管的出现以及隔膜形成。这些形态学事件与核数的相关性使它们能够作为复制周期的标志。早期复制周期标志已在构巢曲霉中得到表征，但在其他丝状真菌中尚未有相关研究。为了更深入了解丝状真菌中复制周期的控制，开展了一项研究来比较烟曲霉和构巢曲霉中标志事件的时间。在烟曲霉中，核复制大约需要45分钟，有丝分裂约占这段时间的5%。在相同条件下，构巢曲霉的核复制大约需要60分钟，有丝分裂约占这段时间的4%。在烟曲霉中，22%的细胞在第一次有丝分裂之前发生了从各向同性到极性的转变，而在构巢曲霉中，直到第一次有丝分裂之后才发生从各向同性到极性的转变。在烟曲霉和构巢曲霉中，分生孢子中最早出现第二个芽管都发生在第三次有丝分裂之后。然而，到第五次有丝分裂时，只有19%的烟曲霉分生孢子有第二个芽管，相比之下，构巢曲霉分生孢子的这一比例为98%。在烟曲霉和构巢曲霉中，第一个隔膜的形成都发生在第四次有丝分裂之后。在所有实验中，少数细胞在核数上落后于其他细胞。在这个延迟的群体中，常见到在较早的有丝分裂时出现标志事件。烟曲霉和构巢曲霉中相同标志事件出现时核数的差异，以及延迟细胞中有丝分裂和标志事件的解偶联表明，核分裂和形态发生处于平行途径，可能由检查点协调。
