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Mitosis and the phylogeny of Taphrina. Can. J. Bot. 60: 1696-1725.Details of mitosis are described by serial-section electron microscopy of synchronized yeast-phase cultures of five species of Taphrina. Based primarily on the morphology and behaviour of the nucleus-associated organelles (NAOs) and modes of spindle formation we conclude that three species are typical ascomycetes which have some significant differences in their mitotic systems. Each of two cultures of a fourth species, T. deformans, was apparently a mixed culture. An ascomycete type of mitosis was shared by cells of both cultures, but one culture also had cells with another ascomycete mitotic system characterized by elaborate and unique NAOs, whereas other cells of the second culture contained a basidiomycete mitotic apparatus. The fifth species contained a typical basidiomycetous mitotic system, which indicates that it is misidentified. The detailed differences among the mitotic systems of the true Taphrina species suggest that the genus as a whole is polyphyletic but undoubtedly ascomycetous. However, a previously unreported pattern of spindle formation found in three species is only otherwise known in a red alga, which may support a common ancestry for the red algae and the ascomycetes. New observations pertinent to the mechanisms of mitosis include, in various species, ( a ) evidence for splitting of NAOs, and their attendant spindle microtubule arrays, during prophase, (b) spindle microtubule polymerization adjacent to the nuclear envelope prior to NAO insertion into the envelope, and ( c ) presence of only two to four nonkinetochore microtubules during anaphase-telophase.

Nutrient depletion triggers a series of adaptive processes as part of the unfolded protein response or UPR. These processes reduce stress to the endoplasmic reticulum by enhancing its protein folding capacity or ability to promote the degradation of dysfunctional proteins. Failure to restore ER homeostasis causes the activation of lethal pathways. The expression of a dominant negative mutant of C/EBPβ (Δ184‐C/EBPβ) alters this balance in chicken embryo fibroblasts (CEF). As a result, CEF display enhanced survival upon prolonged nutrient depletion. Starved Δ184‐C/EBPβ–expressing CEF display pronounced features of autophagy characterized by the appearance of large vesicles containing amorphous material, the formation of smaller double‐membrane vesicles (autophagosomes) and processing of LC3 and GABARAP. However, there were marked differences in the expression and processing of these proteins. In both normal and Δ184‐C/EBPβ expressing CEF, the lipidated form of LC3 (form II) accumulated during starvation but was detectable even when cells were actively dividing in complete medium. In contrast, GABARAP expression and lipidation were strongly stimulated in response to starvation. Inhibition of LC3 expression by RNA interference led to apoptosis in normal CEF even in the absence of starvation but stable and near complete repression of GABARAP was tolerated. Moreover, the inhibition of GABARAP enhanced CEF survival and abolished the expression of the pro‐apoptotic CHOP factor in conditions of starvation, suggesting a reduced level of ER stress. Therefore, GABARAP is a determinant of apoptosis in CEF subjected to prolonged nutrient depletion. J. Cell. Physiol. 230: 1475–1488, 2015. © 2014 Wiley Periodicals, Inc., A Wiley Company

The mitotic nuclear (equivalent to cell) cycle of the oomycete fungus, Saprolegnia ferax, was analysed by quantitative serial-section electron microscopy of hyphal nuclear populations synchronized by inhibition of DNA synthesis by fluorodeoxyuridine (FdUrd). Following telophase and karyokinesis, kinetochore mitrotubules persist into G1 stage as a single group of approximately 42 per nucleus (2n = 42 for this species). During G1 the centrioles replicate and kinetochore microtubules separate into 2 groups of approximately 21, a configuration they retain through S and G2. During metaphase a new population of kinetochore microtubules are formed, each one of an amphitelic pair connecting to the opposite pole to that associated with the persistent microtubule from the previous division. Thus, by the end of metaphase, there are approximately 42 kinetochore microtubules per half spindle. FdUrd, applied for 2 h with uracil, completely blocks DNA synthesis yet permits centriole replication and causes nuclei to accumulate with 2 pairs of centrioles, 2 arrays (each of 21) of kinetochore microtubules, and apparently enlarged nucleoli. Removal of FdUrd permits rapid (within 30 min) DNA synthesis followed by successive rounds of decreasingly synchronous nuclear cycles. These post-FdUrd cycles are 2.5 times longer than normal at 2.5 h, with S plus G2 being more extended than other phases. Calculated durations of a normal nuclear cycle are: G1, 33 min; S, 7 min; G2, 10 min; metaphase, 8 min; anaphase, 0.5 min; and telophase, 4 min.