Subaerial algae of Navajo National Monument, Arizona

Samples from soils and other xeric substrates in Navajo National Monument, Navajo County, Arizona, were collected in 1978. After being moistened with deionized water for three days, these samples were analyzed for algae. Thirty algal taxa were identified. Five species of filamentous Cyanophyta comprised the majority of the biomass. Diatoms were ubiquitous in the soils although low in density. Diatom floras were very similar throughout the monument. Well-developed algal crusts were common in sites where grazing and excessive litter were absent.     

Introduction to the symposium on soil crust communities

Soil crust communities in semiarid and arid lands around the world have received increasing attention in the past two decades. A symposium on their ecology was presented at the annual meeting of the American Bryological and Lichenological Society held in 1991 in San Antonio, Texas. An introduction to the topic and an overview of the papers appearing in the proceedings volume are given in this prologue.     

Diatoms in recent bottom sediments and trophic status of eight lakes and reservoirs in northeastern Utah

Recent bottom sediments of eight lakes and reservoirs in northeastern Utah were examined. One hundred and sixty-four diatom taxa were identified and their relative abundances determined. Seven stand associations were evident by cluster analysis of similarity indices. These association patterns mirrored trophic status of the waters. Shannon-Wiener species diversity values were also determined. The diversities fell in patterns that were similar to the stand associations determined by cluster analysis. The most prevalent diatom taxa encountered in this study were found mostly in eutrophic waters. These taxa included Stephanodiscus astraea, Stephanodiscus astraea var. minutula, Asterionella formosa, and Fragilaria crotonensis. A wide variety of other taxa dominated various mesotrophic and oligotrophic sites.         

Occurrence of Phaedactylum Tricornutum in the Great Salt Lake, Utah, USA

The diatom Phaedactylum tricornutum Bohlin forms blooms in the south arm of the Great Salt Lake, Utah, during cool months. This represents the first report of this taxon from Utah and the first from nonmarine waters in the United States.     

Cryptogamic soil crusts: seasonal variation in algal populations in the Tintic Mountains, Juab County, Utah

The soil algae in the Tintic Mountains, Juab County, Utah, was studied over a one-year period in 1982 and 1983. Fluorescence microscopy was used to measure algal density in samples directly from the field. A total of 30 algal taxa was observed, blue-green algae being most abundant both in terms of density and number of species. Algal density showed peaks in late fall and late spring. Minima were present in September 1982 and July 1983. Several weak correlations between algal density and climatic data existed. In general algae correlated positively with precipitation and negatively with temperature. A combination of low precipitation and hot temperatures was likely responsible for the low density observed in July. The Chrysophyta followed slightly different trends than the other algal groups, having minima in early October 1982 and late August 1983. Field observations indicated that the degree of algal crusting varied noticeably over a period of one year, with highest abundance of hummocking in spring. Heavy summer thunderstorms destroyed algal crusting during July and August of 1983, though absolute density of algae increased during this time in response to the extra moisture.     

Changes in major liver constituents following hypophysectomy in goldfish (Carassius auratus).

The increase in the size of goldfish (Carassius auratus) liver following hypophysectomy is due to a net accumulation of glycogen and the addition of water to maintain a constant proportion with no change in the absolute amount of either protein or lipid.     

Puzzles, promises and a cure for ageing

Recent discoveries in the science of ageing indicate that lifespan in model organisms such as yeast, nematodes, flies and mice is plastic and can be manipulated by genetic, nutritional or pharmacological intervention. A better understanding of the targets of such interventions, as well as the proximate causes of ageing-related degeneration and disease, is essential before we can evaluate if abrogation of human senescence is a realistic prospect.     

Misfolded proteins partition between two distinct quality control compartments

The accumulation of misfolded proteins in intracellular amyloid inclusions, typical of many neurodegenerative disorders including Huntington's and prion disease, is thought to occur after failure of the cellular protein quality control mechanisms. Here we examine the formation of misfolded protein inclusions in the eukaryotic cytosol of yeast and mammalian cell culture models. We identify two intracellular compartments for the sequestration of misfolded cytosolic proteins. Partition of quality control substrates to either compartment seems to depend on their ubiquitination status and aggregation state. Soluble ubiquitinated misfolded proteins accumulate in a juxtanuclear compartment where proteasomes are concentrated. In contrast, terminally aggregated proteins are sequestered in a perivacuolar inclusion. Notably, disease-associated Huntingtin and prion proteins are preferentially directed to the perivacuolar compartment. Enhancing ubiquitination of a prion protein suffices to promote its delivery to the juxtanuclear inclusion. Our findings provide a framework for understanding the preferential accumulation of amyloidogenic proteins in inclusions linked to human disease.     

A nuclear Argonaute promotes multigenerational epigenetic inheritance and germline immortality

Epigenetic information is frequently erased near the start of each new generation. In some cases, however, epigenetic information can be transmitted from parent to progeny (multigenerational epigenetic inheritance). A particularly notable example of this type of epigenetic inheritance is double-stranded RNA-mediated gene silencing in Caenorhabditis elegans. This RNA-mediated interference (RNAi) can be inherited for more than five generations. To understand this process, here we conduct a genetic screen for nematodes defective in transmitting RNAi silencing signals to future generations. This screen identified the heritable RNAi defective 1 (hrde-1) gene. hrde-1 encodes an Argonaute protein that associates with small interfering RNAs in the germ cells of progeny of animals exposed to double-stranded RNA. In the nuclei of these germ cells, HRDE-1 engages the nuclear RNAi defective pathway to direct the trimethylation of histone H3 at Lys?9 (H3K9me3) at RNAi-targeted genomic loci and promote RNAi inheritance. Under normal growth conditions, HRDE-1 associates with endogenously expressed short interfering RNAs, which direct nuclear gene silencing in germ cells. In hrde-1- or nuclear RNAi-deficient animals, germline silencing is lost over generational time. Concurrently, these animals exhibit steadily worsening defects in gamete formation and function that ultimately lead to sterility. These results establish that the Argonaute protein HRDE-1 directs gene-silencing events in germ-cell nuclei that drive multigenerational RNAi inheritance and promote immortality of the germ-cell lineage. We propose that C. elegans use the RNAi inheritance machinery to transmit epigenetic information, accrued by past generations, into future generations to regulate important biological processes.