Hansenula Polymorpha Vac8: A Vacuolar Membrane Protein Required for Vacuole Inheritance and Nucleus-Vacuole Junction Formation

Saccharomyces cerevisiae Vac8 is a vacuolar membrane protein, which functions in vacuole inheritance and fusion, nucleus-vacuole junctions, autophagy and the cytoplasm-to-vacuole-targeting pathway. Here, we analyzed Vac8 of the yeast Hansenula polymorpha. We show that HpVac8 localizes to the vacuolar membrane and concentrates in patches at nucleus-vacuole junctions. Analysis of a VAC8 deletion strain indicated that HpVac8 is required for vacuole inheritance and the formation of nuclear-vacuole junctions, but not for vacuole fusion. Previously, organelle proteomics resulted in the identification of Vac8 in peroxisomal fractions isolated from H. polymorpha and S. cerevisiae. However, deletion of H. polymorpha VAC8 had no effect on peroxisome biogenesis or peroxisome-vacuole contact sites.

The occurrence of nuclear fusion in the amoebal phase of the slime mold Echinostelium minutum: a reinterpretation of the significance of this phenomenon

Nuclear fusion occurs in less than 1% of the myxamoebae of Echinostelium minutum de Bary, isolate D-3, sublines 1965 and 1971. Binucleate amoebae undergo synchronous mitosis, the two nuclei fuse, the fusion nucleus divides, cytokinesis occurs, and uninucleate daughter cells are formed. Failure to find a haploid–diploid alternance between the amoebal and plasmodial phases using Feulgen cytophotometry suggests that nuclear fusion is not a prerequisite for plasmodial formation in this isolate. Nuclear fusion may be one of the mechanisms which has led to the polyploid condition of the 1971 subline. This phenomenon may also represent a parasexual process.

A CYTOPHOTOMETRIC INVESTIGATION OF THE RELATIONSHIP OF DNA AND RNA SYNTHESIS TO ASCUS DEVELOPMENT IN SORDARIA FIMICOLA

Results from quantitative cytochemical analyses of Feulgen-DNA and azure B-RNA content of different stages of ascus development in the pyrenomycete Sordaria fimicola Ces. and DeNot. may be summarized as follows: (a) DNA replication in nuclei of the prefusion ascus (penultimate cell) precedes karyogamy, hence the prefusion nuclei are 2C (replicated haploid), and the fusion nucleus 4C (replicated diploid) in DNA content. These data show that premeiotic S phase and genetic recombination cannot be coincident since DNA replication is complete prior to nuclear fusion in the crozier penultimate cell. (b) DNA replication in the basal and terminal cell nuclei of the crazier does not occur until DNA replication is complete in the subterminal (penultimate) cell. Therefore, DNA replication occurs first in the cell which forms the primary ascus. (c) During ascus enlargement, which occurs during pachytene and diplotene, the total ascus RNA content increases from 18.9 to 195.4 arbitrary units (a.u.), while at the same time nucleolar RNA increases from 0.5 to 1.7 a.u. The concurrent increase in nucleolar and ascus RNA suggests that a rather substantial proportion of the increase in total ascus RNA may be due to the synthesis of ribosomal RNA. (d) In asci which contain binucleate ascospores the total RNA content has increased to 281.5 units. This increase may represent a storage of RNA to be utilized for protein synthesis during the subsequent germination of the ascospore. (e) Ascospores in mature asci of eight day old cultures were always multinucleate. The multinucleate condition is presumably established in preparation for ascospore germination and the initial growth of the germ tube.

Ascocarp development of Eutypella parasitica

Perithecial initials of Eutypella parasitica were found during the spring in bark phellem of cankered sugar maples. These initials were commonly intermingled with mature perithecia probably produced in the current year. One or several ascogonial coils appeared in these initials, but no trichogyne-like hyphae were seen in the archicarp. Asci developed rapidly from croziers formed on ascogenous hyphae and enlarged almost to their mature size before the diploid fusion nucleus divided to form the eight ascospores. The perithecium of E. parasitica has a Xylaria-type centrum as defined by Luttrell in 1951.

The genetics of Cochliobolus spiciferus. I. Genetic inhibition of perithecial and ascus formation

The present investigation showed that certain conidial isolates of C. spiciferus exhibit complete mating inhibition, although the matings consisted of pairings between opposite compatibility types. Other isolates of opposite compatibility produced only sterile perithecia when mated under favorable cultural conditions. It was determined through a genetic analysis that perithecial inhibition in C. spiciferus is conditioned by the presence of the recessive allelic forms, in the homozygous condition in the fusion nucleus at either of two loci designated as I1 and I2. The formation of asci in matings between strains of opposite compatibility was found to be inhibited when both isolates of the mating contain the recessive form of a third gene designated as S.The results are discussed in connection with their significance in assessing the biological relationship of C. spiciferus to other members of the genus Cochliobolus and to members of the genus Curvularia.

ROSELLINIA LIMONIISPORA: NUCLEAR CHANGES IN THE DEVELOPING ASCUS

The nuclear cycle in the developing ascus of Rosellinia limoniispora, as revealed in aceto-orcein and acetocarmine smears, follows the general pattern for the higher Ascomycetes: crozier formation, early synapsis of homologous chromosomes in the fusion nucleus followed by nucleolar fusion, rapid elongation of chromosomes and ascus up to late pachytene of prophase I followed by contraction of the chromosomes and nucleolus, and the formation of eight nuclei as a result of two meiotic and one mitotic divisions. The orientation of nuclei in divisions II and III is haphazard. Ascospore delimitation is by simple cleavage of the cytoplasm; no centriole – astral ray mechanism was observed. A nuclear division occurs in each young ascospore, one daughter nucleus being cut off into a cell and degenerating.

Nuclear reorganization in non-sporing bacteria

1. The process of nuclear fusion and reorganization as it occurs in members of the Bacteriaceae is described.2. The chromosomes behave as pairs at all times, the normal bacillus, of smooth morphology, contains two pairs.3. The fusion nucleus contains three pairs and is preceded by a corresponding trinucleate bacillus.4. One division of the chromosomes takes place in the fusion nucleus, and another during the process of redistribution of the chromosomes. The second division is followed by fragmentation, and return to the bacillary condition.

A CULTURAL AND CYTOLOGICAL INVESTIGATION OF A TWO-SPORED BASIDIOMYCETE, ALEURODISCUS CANADENSIS n. sp.

A new species of Aleurodiscus is described and designated Aleurodiscus canadensis. The basidia of this fungus are regularly two-spored, but occasionally basidia bearing three spores or rarely one spore are encountered. From the cultural and cytological evidence presented the normal life cycle may be described as follows. The cells of the subhymenium are dikaryotic with clamp connections. The young basidia are at first binucleate. Following karyogamy the fusion nucleus undergoes reduction division producing the usual tetrad of nuclei. Each spore of the two-spored basidium receives two of the four daughter nuclei. The two nuclei in these spores undergo further division while the spore is still attached or shortly after discharge, so that the mature spore contains four nuclei. Such a spore is capable of producing a mycelium bearing clamp connections. Although the majority of the spores produce mycelia with clamp connections, a spore may occasionally develop a mycelium that does not bear clamps. When such exceptional mycelia are mated in compatible combinations, dikaryotic mycelia with clamp connections are obtained. From the mating of a number of these exceptional haplonts the heterothallic and bipolar relationship is made evident. Although complete cytological information on the spores that give rise to these exceptional haploid mycelia is lacking, it is probable that these spores are originally uninucleate and that this results from the distribution of the four nuclei in a three-spored basidium in such a way that one spore receives two nuclei and the other two spores one nucleus each. The two nuceli that migrate into the normal spore, therefore, probably bear allelomorphic inter-fertility factors. If this species can be considered homothallic, the homothallism is a different type from that found in species that complete their life cycle from the development of a single uninucleate spore. The necessity for such a distinction is stressed.