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Biomedical subjects

A L Dawe

Publications and source records attributed to A L Dawe.

7 recordsLinked to original sources
PubMed2001

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.

Animals↗
PubMed2001

Hypoviruses and chestnut blight: exploiting viruses to understand and modulate fungal pathogenesis.

Fungal viruses are considered unconventional because they lack an extracellular route of infection and persistently infect their hosts, often in the absence of apparent symptoms. Because mycoviruses are limited to intracellular modes of transmission, they can be considered as intrinsic fungal genetic elements. Such long-term genetic interactions, even involving apparently asymptomatic mycoviruses, are likely to have an impact on fungal ecology and evolution. One of the clearest examples supporting this view is the phenomenon of hypovirulence (virulence attenuation) observed for strains of the chestnut blight fungus, Cryphonectria parasitica, harboring members of the virus family Hypoviridae. The goal of this chapter is to document recent advances in hypovirus molecular genetics and to provide examples of how that progress is leading to the identification of virus-encoded determinants responsible for altering fungal host phenotype, insights into essential and dispensable elements of hypovirus replication, revelations concerning the role of G-protein signaling in fungal pathogenesis, and new avenues for enhancing biological control potential.

Ascomycota↗
PubMed1997

Novel modifications to the farnesyl moiety of the a-factor lipopeptide pheromone from Saccharomyces cerevisiae: a role for isoprene modifications in ligand presentation.

The a-factor of Saccharomyces cerevisiae is a dodecapeptide pheromone [YIIKGVFWDPAC(farnesyl)-OCH3] in which posttranslational modification with a farnesyl isoprenoid and carboxymethyl group is required for full biological activity. Utilizing novel synthetic techniques and a well-characterized array of biological assays, we prepared original modifications to the farnesyl moiety of the pheromone in order to assess the importance of this part of the lipopeptide for biological activity. Specifically, the 3-methyl group was replaced to create analogs containing the ethyl, vinyl, tert-butyl, and phenyl moieties at the 3-position of the farnesyl chain. Subsequent biological analyses demonstrated that all of these modifications render an active pheromone, with the vinyl and ethyl analogs exhibiting higher activity than the native a-factor. However, the level of activity varied with the modification; the bulkier and more hydrophobic groups (tert-butyl and phenyl) exhibited lower biological activity than the smaller moieties (ethyl and vinyl). Furthermore, two analogs with phenyl substitutions that differ only in the presumed isomerization of the allylic double bond show up to an 8-fold difference in bioactivity. It has previously been surmised that the role of isoprenoid additions is solely to target the attached polypeptides to membranes by increasing their hydrophobicity. However, these studies demonstrate that even modest structural changes to the isoprenoid can significantly affect biological activity. These results are clearly inconsistent with a simple hydrophobic role for the isoprenoid and instead illustrate that it plays an active role in mediating optimal a-factor/receptor interaction.

Butadienes↗
PubMed1997

Deletion of nudC, a nuclear migration gene of Aspergillus nidulans, causes morphological and cell wall abnormalities and is lethal.

Nuclear migration is required for normal development in both higher and lower eukaryotes. In fungi this process is mediated by cytoplasmic dynein. It is believed that this motor protein is anchored to the cell membrane and moves nuclei by capturing and pulling on spindle pole body microtubules. To date, four genes have been identified and shown to be required for this process in Aspergillus nidulans. The nudA and nudG genes, respectively, encode the heavy and light chains of cytoplasmic dynein, and the nudF and nudC gene products encode proteins of 49 and 22 kDa. The precise biochemical functions of the nudF and nudC genes have not yet been identified. In this report we further investigate NUDC protein function by deleting the nudC gene. Surprisingly, although deletion of nudA and nudF affect nuclear migration, deletion of nudC profoundly affected the morphology and composition of the cell wall. Spores of the strain deleted for nudC grew spherically and lysed. The thickness of the cell wall was increased in the deletion mutant and wall polymer composition was abnormal. This phenotype could be repressed by growth on osmotically buffered medium at low temperature. Similar, but less severe, effects were also noted in a strain depleted for NUDC by down-regulation. These results suggest a possible relationship between fungal cell wall biosynthesis and nuclear migration.

Actins↗
PubMed1996

A superactive peptidomimetic analog of a farnesylated dodecapeptide yeast pheromone.

The S. cerevisiae a-factor, YIIKGVFWDPAC(s-farnesyl)-OCH3, is one of two peptide mating pheromones which mediate cell-cell communication in S. cerevisiae. We previously reported that replacing Gly5 with D-Ala led to a 4-6 fold increase in activity while the L-Ala5 homolog was 4 to 16-fold less active than the wildtype. To clarify the structural implications of these findings, we conformationally restricted the center of the pheromone by inserting gamma-lactam constraints in place of either the Lys4Gly5 or the Gly5Val6 dipeptide unit. Incorporation of (R)-3-amino-2-oxo-1-pyrrolidineacetic acid in place of Lys4Gly5 led to a super-active agonist which exhibited a 32-fold higher bioactivity than that of the a-factor. In contrast, an analog with (S)-3-amino-2-oxo-1-pyrrolidineacetic acid in place of Gly5Val6 is about 30 to 60-fold less active than the a-factor. These data strongly suggest that the a-factor adopts a reverse turn as its bioactive conformation.

Amino Acid Sequence↗
PubMed1993

Identification of a hyperactive mating pheromone of Saccharomyces cerevisiae.

The yeast mating pheromone a-factor is a farnesylated peptide [YIIKGVFWDPAC(Farnesyl)-OCH3] involved in the signal transduction cascade which leads to sexual conjugation of haploid cells. We have identified a synthetic analog of the a-factor, [D-Ala5] a-factor, which exhibits 4-6 fold greater biological activity than that of a-factor as judged by two different assay systems. In contrast, [L-Ala5] a-factor has 4-16 fold lower activity than wild-type a-factor. [D-Ala5] a-factor remains susceptible to cleavage by the yeast alpha-cell specific protease a-factorase, thereby ruling out increased activity due to greater stability. This report describes the first example of a hyperactive S. cerevisiae pheromone and may suggest a conformationally preferred form of this lipopeptide ligand.

Amino Acid Sequence↗