Chair Design Affects How Older Adults Rise from a Chair

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111137/1/j.1532-5415.1996.tb06402.x.pd

The evolution of silicon transporters in diatoms

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Phycology 52 (2016): 716–731, doi:10.1111/jpy.12441.Diatoms are highly productive single-celled algae that form an intricately patterned silica cell wall after every cell division. They take up and utilize silicic acid from seawater via silicon transporter (SIT) proteins. This study examined the evolution of the SIT gene family to identify potential genetic adaptations that enable diatoms to thrive in the modern ocean. By searching for sequence homologs in available databases, the diversity of organisms found to encode SITs increased substantially and included all major diatom lineages and other algal protists. A bacterial-encoded gene with homology to SIT sequences was also identified, suggesting that a lateral gene transfer event occurred between bacterial and protist lineages. In diatoms, the SIT genes diverged and diversified to produce five distinct clades. The most basal SIT clades were widely distributed across diatom lineages, while the more derived clades were lineage-specific, which together produced a distinct repertoire of SIT types among major diatom lineages. Differences in the predicted protein functional domains encoded among SIT clades suggest that the divergence of clades resulted in functional diversification among SITs. Both laboratory cultures and natural communities changed transcription of each SIT clade in response to experimental or environmental growth conditions, with distinct transcriptional patterns observed among clades. Together, these data suggest that the diversification of SITs within diatoms led to specialized adaptations among diatoms lineages, and perhaps their dominant ability to take up silicic acid from seawater in diverse environmental conditions.Gordon and Betty Moore Foundation Grant Numbers: GBMF2637, GBMF3776; University of Washington; National Science Foundation Grant Number: OCE-120523

An Experiential Approach to Mentoring Academic Leaders: Review, Practice, Report

This session presents a leadership development program where new department chairs discuss best practices and realistic challenges with seasoned chairs, helping all to improve their leadership skills through a supportive group process. The program includes a summer book study, monthly meetings, a department chair handbook, and leadership resources

Genome size differentiates co-occurring populations of the planktonic diatom Ditylum brightwellii (Bacillariophyta)

<p>Abstract</p> <p>Background</p> <p>Diatoms are one of the most species-rich groups of eukaryotic microbes known. Diatoms are also the only group of eukaryotic micro-algae with a diplontic life history, suggesting that the ancestral diatom switched to a life history dominated by a duplicated genome. A key mechanism of speciation among diatoms could be a propensity for additional stable genome duplications. Across eukaryotic taxa, genome size is directly correlated to cell size and inversely correlated to physiological rates. Differences in relative genome size, cell size, and acclimated growth rates were analyzed in isolates of the diatom <it>Ditylum brightwellii</it>. <it>Ditylum brightwellii </it>consists of two main populations with identical 18s rDNA sequences; one population is distributed globally at temperate latitudes and the second appears to be localized to the Pacific Northwest coast of the USA. These two populations co-occur within the Puget Sound estuary of WA, USA, although their peak abundances differ depending on local conditions.</p> <p>Results</p> <p>All isolates from the more regionally-localized population (population 2) possessed 1.94 ± 0.74 times the amount of DNA, grew more slowly, and were generally larger than isolates from the more globally distributed population (population 1). The ITS1 sequences, cell sizes, and genome sizes of isolates from New Zealand were the same as population 1 isolates from Puget Sound, but their growth rates were within the range of the slower-growing population 2 isolates. Importantly, the observed genome size difference between isolates from the two populations was stable regardless of time in culture or the changes in cell size that accompany the diatom life history.</p> <p>Conclusions</p> <p>The observed two-fold difference in genome size between the <it>D. brightwellii </it>populations suggests that whole genome duplication occurred within cells of population 1 ultimately giving rise to population 2 cells. The apparent regional localization of population 2 is consistent with a recent divergence between the populations, which are likely cryptic species. Genome size variation is known to occur in other diatom genera; we hypothesize that genome duplication may be an active and important mechanism of genetic and physiological diversification and speciation in diatoms.</p

Interim Leadership Positions: The Kobayashi Maru of Academia?

Leading a department through a transition such as reorganization or restructuring is difficult. When the unit leader is in an interim position, this is even more complicated. This presentation will be led by faculty who were all in interim leadership positions during major transitions in leadership, restructuring, and staff layoffs

A Novel Single-Domain Na+-Selective Voltage-Gated Channel in Photosynthetic Eukaryotes

The evolution of Na+-selective four-domain voltage-gated channels (4D-Navs) in animals allowed rapid Na+-dependent electrical excitability, and enabled the development of sophisticated systems for rapid and long-range signaling. While bacteria encode single-domain Na+-selective voltage-gated channels (BacNav), they typically exhibit much slower kinetics than 4D-Navs, and are not thought to have crossed the prokaryote–eukaryote boundary. As such, the capacity for rapid Na+-selective signaling is considered to be confined to certain animal taxa, and absent from photosynthetic eukaryotes. Certainly, in land plants, such as the Venus flytrap (Dionaea muscipula) where fast electrical excitability has been described, this is most likely based on fast anion channels. Here, we report a unique class of eukaryotic Na+-selective, single-domain channels (EukCatBs) that are present primarily in haptophyte algae, including the ecologically important calcifying coccolithophores, Emiliania huxleyi and Scyphosphaera apsteinii. The EukCatB channels exhibit very rapid voltage-dependent activation and inactivation kinetics, and isoform-specific sensitivity to the highly selective 4D-Nav blocker tetrodotoxin. The results demonstrate that the capacity for rapid Na+-based signaling in eukaryotes is not restricted to animals or to the presence of 4D-Navs. The EukCatB channels therefore represent an independent evolution of fast Na+-based electrical signaling in eukaryotes that likely contribute to sophisticated cellular control mechanisms operating on very short time scales in unicellular algae

Alternative Mechanisms for Fast Na+/Ca2+ Signaling in Eukaryotes via a Novel Class of Single-Domain Voltage-Gated Channels

This is the final version. Available from Elsevier via the DOI in this record.Rapid Na+/Ca2+-based action potentials govern essential cellular functions in eukaryotes, from the motile responses of unicellular protists, such as Paramecium [1, 2], to complex animal neuromuscular activity [3]. A key innovation underpinning this fundamental signaling process has been the evolution of four-domain voltage-gated Na+/Ca2+ channels (4D-Cavs/Navs). These channels are widely distributed across eukaryote diversity [4], albeit several eukaryotes, including land plants and fungi, have lost voltage-sensitive 4D-Cav/Navs [5, 6, 7]. Because these lineages appear to lack rapid Na+/Ca2+-based action potentials, 4D-Cav/Navs are generally considered necessary for fast Na+/Ca2+-based signaling [7]. However, the cellular mechanisms underpinning the membrane physiology of many eukaryotes remain unexamined. Eukaryotic phytoplankton critically influence our climate as major primary producers. Several taxa, including the globally abundant diatoms, exhibit membrane excitability [8, 9, 10]. We previously demonstrated that certain diatom genomes encode 4D-Cav/Navs [4] but also proteins of unknown function, resembling prokaryote single-domain, voltage-gated Na+ channels (BacNavs) [4]. Here, we show that single-domain channels are actually broadly distributed across major eukaryote phytoplankton lineages and represent three novel classes of single-domain channels, which we refer collectively to as EukCats. Functional characterization of diatom EukCatAs indicates that they are voltage-gated Na+- and Ca2+-permeable channels, with rapid kinetics resembling metazoan 4D-Cavs/Navs. In Phaeodactylum tricornutum, which lacks 4D-Cav/Navs, EukCatAs underpin voltage-activated Ca2+ signaling important for membrane excitability, and mutants exhibit impaired motility. EukCatAs therefore provide alternative mechanisms for rapid Na+/Ca2+ signaling in eukaryotes and may functionally replace 4D-Cavs/Navs in pennate diatoms. Marine phytoplankton thus possess unique signaling mechanisms that may be key to environmental sensing in the oceans.European Research CouncilNS

Sexual Reproduction in the Marine Centric Diatom Ditylum Brightwellii

Sexual reproduction is an essential phase in the life history of diatoms that serves to maintain high levels of genetic diversity and to restore large cells to a population. However, complete life cycles of most diatoms are unknown, and observations of sexual reproduction in nature are rare. Culture studies and field observations of Ditylum brightwellii (West ) Grunow in Van Heurck, a centric marine diatom, were used to clarify confusion generated from previous studies of the sexual cycle, to determine the mating system, and to examine natural populations for the incidence of sexual reproduction. Clones of D. brightwellii isolated from Wadsworth Cove, Castine, Maine, were used to observe the morphology of sexual stages. These clones were then studied to determine their mating system and their potential to self-fertilize or outcross. Results from this study show that sexual reproduction in Ditylum brightwellii is homothallic; two naked, spherical eggs and an estimated 64 uniflagellate sperm are released simultaneously from each gametangium into nutrient-replete medium. Oogenesis and spermatogenesis appear to be determined by size; larger clones produced predominately eggs whereas smaller clones produced predominately sperm. Sperm were attracted to the eggs, and size regeneration progressed from a putatively fertilized egg via a true auxospore. Ditylum brightwellii had high gametogenic potential, and self-fertilization was vigorous in some clonal cultures. However, outcrossing was also important in the mating system. Vegetative cell enlargement occurred in older, nutrient-depleted cultures, and produced interme&ate-sized cells. The size structure of natural populations of D. brightwellii in Wadsworth Cove was monitored weekly from 31 August to 7 December, 2004. The size frequency distributions of these populations were mainly unimodal throughout autumn, but appeared to have gradual shifts in size. The smallest cells were found in an early autumn population, whereas, the largest cells, including cells within the size range of initial cells measured in the laboratory (59 a 5 SD pm), appeared in mid-autumn. Spennatogonangia and large, polar cells were found concurrently in Wadsworth Cove in mid-autumn, 2004, suggesting that sexual reproduction was occurring in nature at this time

Genomic evidence of speciation and adaptation in diatoms

Diatoms are one of the most ecologically important groups of organisms in the ocean. They are the youngest and most species-rich group of phytoplankton, having colonized both marine and terrestrial ecosystems. The ocean is constantly changing, and understanding the mechanisms of species-diversification and adaptation in diatoms is important to assessing their resilience to future environmental changes. Speciation and adaptation were investigated in three diatom genera using genomic and genetic signals. One mechanism of speciation was tested by bringing isolates of two populations of the planktonic diatom Ditylum brightwellii into the lab to measure genome size differences indicated by cell size differences in the field. Genome sizes differed by two-fold between individuals of each population, suggesting that the populations are in fact cryptic species, thus corroborating previous research indicating reproductive isolation between the populations. Growth rates of Ditylum isolates from within a species differed significantly depending on where they were collected, southern or northern Pacific Ocean, suggesting that they were differentially adapted to their local environments. Natural selection acts directly on phenotypes; positively selected genes control those phenotypes and their sequences vary among populations and between species. Positively selected genes were investigated in Pseudo-nitzschia, Ditylum and Thalassiosira, but the greatest number of selected genes was found within a single species, Thalassiosira pseudonana. All of the protein coding genes from seven strains of T. pseudonana were analyzed and 809 (7%) were found to be positively selected. These genes encode protein-binding proteins, transcriptional regulators, and proteins associated with cell signaling and the cell wall. One quarter of the positively selected genes was novel to T. pseudonana, thus differentiating this species while conferring a selective advantage to individuals. Genome duplications, such as occurred in D. brightwellii, provide an opportunity for increased genetic variability upon which selection may act under changing environments. In the absence of polyploidization, genetic variability is maintained through mutations accrued during each round of cell division. The positively selected genes presented here for T. pseudonana provide future opportunities to test hypotheses concentrated on linking genotypes of positively selected genes with the phenotypes that they control and their associated selective pressures

Brevetoxin and Conotoxin Interactions with Single-Domain Voltage-Gated Sodium Channels from a Diatom and Coccolithophore

The recently characterized single-domain voltage-gated ion channels from eukaryotic protists (EukCats) provide an array of novel channel proteins upon which to test the pharmacology of both clinically and environmentally relevant marine toxins. Here, we examined the effects of the hydrophilic µ-CTx PIIIA and the lipophilic brevetoxins PbTx-2 and PbTx-3 on heterologously expressed EukCat ion channels from a marine diatom and coccolithophore. Surprisingly, none of the toxins inhibited the peak currents evoked by the two EukCats tested. The lack of homology in the outer pore elements of the channel may disrupt the binding of µ-CTx PIIIA, while major structural differences between mammalian sodium channels and the C-terminal domains of the EukCats may diminish interactions with the brevetoxins. However, all three toxins produced significant negative shifts in the voltage dependence of activation and steady state inactivation, suggesting alternative and state-dependent binding conformations that potentially lead to changes in the excitability of the phytoplankton themselves