Septal involvement in nuclear migration inSchizophyllum commune

Summary A system, utilizing thedwarf andpuff morphological mutants ofSchizophyllum commune, was devised to select specific hyphal segments that were in different stages of septal dissolution and nuclear migration. These stages were observed with the electron microscope. Direct evidence of the dissolution of complex septal during nuclear migration was obtained. Initially there was a disruption of the septal swelling, followed by erosion of the remaining cross wall. Complex septa were therepy converted to simple septa through which nuclei migrated. These septa were covered with secondary cell wall material. Following nuclear migration only vacuolate hyphae with remnant membrane structures remained. Occasionally, intact hyphae were observed within these vacuolate hyphae.     

Kinetics,nutrition and inhibitor properties of basidiospore germination in schizophyllum commune

Summary The kinetics, nutritional requirements and inhibitor properties of basidiospore germination in the wood-rotting mushroom Schizophyllum commune were investigated. Measurements of changes in absorbancy and dry weight showed a lag period of approximately 15–20 hrs, followed by an abrupt increase in the rate of both processes. Individual basidiospore elongation also showed a lag phase and population changes were heterogenous in this regard.Carbohydrates active for basidiospore germination were grouped into four categories. Those sugars active between 15 and 20 hrs included glycogen, turanose, cellobiose, maltose, sucrose, glucose, fructose, mannose, galactose and xylose. Several sugar alcohols were only active between 30 and 60 hrs incubation and these included mannitol, sorbitol, ribitol, xylitol, arabitol, erythritol and glycerol. A third category of carbohydrates active for germination required prolonged incubation between 30 hrs and 7 days and included lactose, sorbose, raffinose, melezitose, trehalose, ribose and melibiose. Compounds without activity after 7 days included galactitol, inositol, acetate, succinate, gluconate, citrate, fumarate, rhamnose, fucose and inulin.Nitrogen sources active in basidiospore germination included complex organic nitrogenous substrates, asparagine, glutamine, arginine, urea and various ammonium salts.Germination was inhibited by cycloheximide, l-ethionine, p-fluoro-dl-phenylalanine, sodium azide, 2,4-dinitrophenol, phenylmercuric acetate and 2-deoxy-d-glucose. Alkali as a trapping agent arrested germination in glucose-(NH₄)₂SO₄ medium but was without ill-effect in glucose peptone broth.     

Mating types and pheromone recognition in the Homobasidiomycete schizophyllum commune.

In the homobasidiomycete Schizophyllum commune the mating type genes of the B locus encode pheromones and pheromone receptors in multiple allelic specificities. Interaction of non-self pheromones and receptors leads to induction of B-regulated development easily scored in S. commune by the "flat" phenotype which lacks aerial mycelium formation and shows aberrant hyphal morphology. In contrast, self pheromones are not recognized and B-regulated development is not induced. Natural and mutant alleles of receptors have been analyzed for their specificity in transformation assays, and parts of the receptor involved in ligand discrimination can be described. The biological role of pheromone response in S. commune is assumed to be connected to nuclear migration based on the observation that wild-type cells with a receptor gene of different specificity lead to cells capable of nuclear uptake. Other possible roles for pheromone function are discussed.     

Occurrence of microtubules in the hyphae of Schizophyllum commune during intercellular nuclear migration

Summary During the intercellular nuclear migration of the basidiomycete Schizophyllum commune cytoplasmic microtubules were frequently observed scattered in the hyphae around interphase nuclei and connected with a semiglobular structure at the poles of mitotic and postmitotic nuclei. Thus it seems possible that microtubules, which have been demonstrated to participate in the intracellular nuclear movements in the dikaryotic hyphae of the basidiomycetes, are also involved in the intercellular nuclear movements of these fungi. During hyphal fusion microtubules close to an interphase nucleus were connected with electron-dense structures. It is suggested that these structures are centers for the assembly of microtubules necessary for nuclear movements not associated with nuclear divisions.Abbreviations KCE kinetochore equivalent - ch chromatin - cw cross wall of septum - ge semiglobular end of KCE - gm grey material - m mitochondrion - mp middle plate of KCE - mt microtubules - n nucleus - ne nuclear envelope - nu nucleolus - s electron-dense structure connected with microtubules     

Kinetic studies of septum synthesis,erosion and nuclear migration in a growing B-mutant of Schizophyllum commune

Summary Microscopic measurements of apical growth and primary branch elongation were compared with nuclear movements, septum synthesis and erosion in a growing B-mutant of Schizophyllum commune. Apical growth, mitosis, septum formation, and intercalary cell division were similar to wild-type hyphae. Nuclear replication and new cross-wall formation also occurred in either apical cells bounded by eroding septa or in subterminal cells adjoined by eroded septa. An anucleate subterminal unit of the B-mutant hypha was invaded by a migrant nucleus which subsequently replicated and laid down a new septum in this region. Septum erosion occurred as early as 1 h following synthesis. Cellular granules and filaments were implicated in both septum synthesis and erosion.     

Unusual structure of nuclei in a B–mutant strain of Schizophyllum commune with intercellular nuclear migration

Serial sections of multinucleate hyphae of a B–mutant strain of Schizophyllum commune , in which intercellular nuclear migration takes place, revealed appendages attached to nuclei. The appendages were strand–like organelles surrounded by a membrane with an electron–dense content. In addition, the outer membranes of the envelopes of adjacent nuclei were often joined and surface sections of these nuclei showed fibrous material with only a few nuclear pores. These ultrastructural features have not been reported before in the vegetative hyphae of S. commune , and they are suggested to be necessary for intercellular nuclear movement. The appendages may create the force or may result from the force necessary for the movement of the nucleus, while the joining of the outer membranes of the nuclear envelopes makes possible simultaneous movement of several nuclei, although only one has an appendage. The fibrous material in the nuclear envelope may facilitate sliding of the nuclei through the cytoplasm.     

The relationship between megakaryocyte nuclear DNA content and gene expression

Megakaryocytes are a distinct population of bone marrow cells that have the unique feature of increasing their DNA content without undergoing division. The biological effect of ploidy distribution on gene expression, receptor expression and protein synthesis is still unknown. Using molecular hybridization techniques, we have started a systematic analysis of mRNA expression in megakaryocytes for a number of proteins involved in clot formation. These data will be related to ploidy. Platelets are the unnucleated product of megakaryocytes, having their protein content derived from the precursor cell. Therefore, the understanding of the molecular mechanisms regulating megakaryocyte biology and the consequent type and reactivity of platelets produced is of fundamental importance in both physiological and pathological conditions.     

Direct studies of nuclear movements in Schizophyllum commune

Summary Measurements of nuclear positions in apical cells of homokaryotic mycelia and dikaryotic mycelium of Schizophyllum commune showed that nuclei occupied a near central position in most cases. Forward nuclear movements observed in living hyphal apices occurred at rates within the range of hyphal growth and could account for the maintenance of centrally located nuclei. Opposed nuclear movements followed mitosis and greatly exceeded the rate of hyphal growth. Septum disruption and rapid nuclear movements characterized an A _xB_mut homokaryon. Neither cytoplasmic streaming nor actively participating granules or filaments could account for any of these nuclear movements.     

The relationship between nuclear DNA content and leaf strategy in seed plants

BACKGROUND AND AIMS: Species' 2C-values (mass of DNA in G(1) phase 2n nuclei) vary by at least four orders of magnitude among seed plants. The 2C-value has been shown to be co-ordinated with a number of other species traits, and with environmental variables. A prediction that species 2C-values are negatively related to leaf life span (LL) and leaf mass per area (LMA) is tested. These leaf traits are components of a major dimension of ecological variation among plant species. METHODS: Flow cytometry was used to measure the 2C-values for 41 Australian seed plant species, 40 of which were new to the literature. Where possible, LL and LMA data from the global literature were combined with 2C-values from our data set and online C-value databases. KEY RESULTS: Across all species, weak positive relationships were found between 2C-values and both LL and LMA; however, these did not reflect the relationships within either angiosperms or gymnosperms. Across 59 angiosperm species, there were weak negative relationships between 2C-values and both LL (r2 = 0.13, P = 0.005) and LMA (r2 = 0.15, P = 0.002). These relationships were the result of shifts to longer LL and greater LMA in woody compared with herbaceous growth forms, with no relationships present within growth forms. It was not possible to explain a positive relationship between 2C-values and LMA (r2 = 0.30, P = 0.024) across 17 gymnosperm species. The 2C-value was not related to LL or LMA either across species within orders (except for LMA among Pinales), or as radiation divergences in a model phylogeny. CONCLUSIONS: Gymnosperms appear to vary along a spectrum different from angiosperms. Among angiosperms, weak negative cross-species relationships were associated with growth form differences, and traced to a few divergences deep in the model phylogeny. These results suggest that among angiosperms, nuclear DNA content and leaf strategy are unrelated.     

The relationship between a nuclear restorer gene and the nuclear gene for male sterility in Petunia

Summary This paper describes the relationship between the restorer gene and the gene for male sterility in the background of normal cytoplasm. We combined these two traits by crosses in one plant, thus making genetic analysis possible. Two main conclusions can be drawn: 1. The restorer gene and the gene for male sterility are located at different loci which segregate independently one from the other. 2. The Rf allele does not affect the expression of the e allele.Contribution from the Department of Plant Genetics and Breeding, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. 1983 series, No. 779 E     

Evolutionarily conserved nuclear migration genes required for early embryonic development in Caenorhabditis elegans

The nudF and nudC genes of the fungus Aspergillus nidulans encode proteins that are members of two evolutionarily conserved families. In A. nidulans these proteins mediate nuclear migration along the hyphae. The human ortholog of nudF is Lis1, a gene essential for neuronal migration in the developing cerebral cortex. The mammalian ortholog of nudC encodes a protein that interacts with Lis1. We have identified orthologs of nudC and Lis1 from the nematode Caenorhabditis elegans. Heterologous expression of the C. elegans nudC ortholog, nud-1, complements the A. nidulans nudC3 mutant, demonstrating evolutionary conservation of function. A C. elegans nud-1::GFP fusion produces sustained fluorescence in sensory neurons and embryos, and transient fluorescence in the gonad, gut, vulva, ventral cord, and hypodermal seam cells. Fusion of GFP to C. elegans lis-1 revealed expression in all major neuronal processes of the animal as well as the multinucleate spermathecal valves and adult seam cells. Phenotypic analysis of either nud-1 and lis-1 by RNA interference yielded similar phenotypes, including embryonic lethality, sterility, altered vulval morphology, and uncoordinated movement. Digital time-lapse video microscopy was used to determine that RNAi-treated embryos exhibited nuclear positioning defects in early embryonic cell division similar to those reported for dynein/dynactin depletion. These results demonstrate that the LIS-1/NUDC-like proteins of C. elegans represent a link between nuclear positioning, cell division, and neuronal function.     

The relationship between geographic variation in clutch size and migration pattern in the Yellow Wagtail

Clutch size in the Yellow Wagtail increases by about one egg per 19° of latitude throughout Europe, but at a given latitude larger clutches are laid in western than in eastern Europe. In eastern Asia there is evidence of a reverse latitudinal cline, in which clutch size is smaller at higher latitudes, and considerably smaller than in Europe at equivalent latitudes. These trends suggest that smaller clutches are laid by populations with access to extensive wintering areas in east Africa and south-east Asia, whereas larger clutches are laid by populations with more restricted wintering areas in west Africa and India. Higher winter mortality in the latter populations may reduce breeding density, leading to less competition for resources and allowing larger clutches to be produced.     

The relationship between latitude,migration and the evolution of bird song complexity

For the past several decades it has been proposed that birds show latitudinal variation in song complexity. How universal this variation may be and what factors generate it, however, are still largely unknown. Furthermore, while migration is confounded with latitude, migratory behaviour alone may also be associated with variation in song complexity. In this paper we review the literature to assess current ideas on how latitude and migratory behaviour may drive large‐scale geographical patterns of song complexity. At least seven distinct hypotheses have been proposed in 29 studies of the topic. Four of these hypotheses posit that sexual selection pressures co‐vary with latitude and/or migration, resulting in concordant changes in song. Other hypotheses suggest that mechanisms other than sexual selection, such as large‐scale changes in environmental sound transmission properties, may be at play. Sixteen studies found support for increased song complexity with increased latitude and/or migration, whereas 13 did not. Relatively few studies exist on this topic, and methodological differences between them and variable definitions of ‘complexity’ make it difficult to determine whether results are comparable and concordant. At a minimum, it is possible to conclude there is no strong evidence that song complexity increases with latitude and/or migration in all birds. Future work should focus on examining multiple hypotheses at once to further advance our understanding of how latitude, migration and song complexity may or may not be related.     

The relationship between migration and chondrogenic potential of trunk neural crest cells in Ambystoma mexicanum

Based on results of transplantation experiments, it has long been believed that trunk neural crest cells are incapable of chondrogenesis. When pigmented trunk neural crest cells of Ambystoma mexicanum are transplanted to cranial levels of albino (a/a) embryos, the graft cells ultimately produce ectopic fins, but are incapable of following the chondrogenic cranial neural crest pathways. Therefore, heterotopic transplantation does not expose these cells to the same environment experienced by cranial neural crest cells, and is neither an adequate nor a sufficient test of chondrogenic potential. However, in vitro culture of trunk neural crest cells with pharyngeal endoderm does provide a direct test of chondrogenic ability. That cartilage does not form under these conditions demonstrates conclusively that trunk neural crest cells possess no chondrogenic potential.