Oleic acid is an endogenous ligand of TLX/NR2E1 that triggers hippocampal neurogenesis.

Neural stem cells, the source of newborn neurons in the adult hippocampus, are intimately involved in learning and memory, mood, and stress response. Despite considerable progress in understanding the biology of neural stem cells and neurogenesis, regulating the neural stem cell population precisely has remained elusive because we have lacked the specific targets to stimulate their proliferation and neurogenesis. The orphan nuclear receptor TLX/NR2E1 governs neural stem and progenitor cell self-renewal and proliferation, but the precise mechanism by which it accomplishes this is not well understood because its endogenous ligand is not known. Here, we identify oleic acid (18:1ω9 monounsaturated fatty acid) as such a ligand. We first show that oleic acid is critical for neural stem cell survival. Next, we demonstrate that it binds to TLX to convert it from a transcriptional repressor to a transcriptional activator of cell-cycle and neurogenesis genes, which in turn increases neural stem cell mitotic activity and drives hippocampal neurogenesis in mice. Interestingly, oleic acid-activated TLX strongly up-regulates cell cycle genes while only modestly up-regulating neurogenic genes. We propose a model in which sufficient quantities of this endogenous ligand must bind to TLX to trigger the switch to proliferation and drive the progeny toward neuronal lineage. Oleic acid thus serves as a metabolic regulator of TLX activity that can be used to selectively target neural stem cells, paving the way for future therapeutic manipulations to counteract pathogenic impairments of neurogenesis.

Using a five-gene phylogeny to test morphology-based hypotheses of Smittium and allies, endosymbiotic gut fungi (Harpellales) associated with arthropods.

Smittium, one of the first described genera of gut fungi, is part of a larger group of endosymbiotic microorganisms (Harpellales) that live predominantly in the digestive tracts of aquatic insects. As a diverse and species-rich taxon, Smittium has helped to advance our understanding of the gut fungi, in part due to the relative success of attempts to culture species of Smittium as compared to other members of Harpellales. Approximately 40% of the 81 known species of Smittium have been cultured. This is the first Smittium multigene dataset and phylogenetic analysis, using the 18S and 28S rRNA genes, as well as RPB1, RPB2, and MCM7 translated protein sequences. Several well-supported clades were recovered within Smittium. One includes the epitype S. mucronatum (the "True Smittium" clade), and another contains many species including S. simulii and S. orthocladii (the "Parasmittium" clade). Ancestral states were reconstructed for holdfast shape, thallus branching type, as well as asexual (trichospore) and sexual (zygospore) spore morphology. Two of these characters, holdfast shape and trichospore morphology, supported the split of the two main clades revealed by the molecular phylogeny, suggesting these are natural clades and these traits may have evolutionary and perhaps ecological significance.

An eight-gene molecular phylogeny of the Kickxellomycotina, including the first phylogenetic placement of Asellariales.

Kickxellomycotina is a recently described subphylum encompassing four zygomycete orders (Asellariales, Dimargaritales, Harpellales, Kickxellales). These fungi are united by the formation of disciform septal pores containing lenticular plugs. Morphological diversification and life history evolution has made the relationships within and among the four orders difficult to resolve on those grounds alone. Here we infer the phylogeny of the Kickxellomycotina based on an eight-gene supermatrix including both ribosomal rDNA (18S, 28S, 5.8S) and protein sequences (MCM7, TSR1, RPB1, RPB2, ß-tubulin). The results of this study demonstrate that Kickxellomycotina is monophyletic and related to members of the Zoopagomycotina. Eight unique clades are distinguished in the Kickxellomycotina, including the four defined orders (Asellariales, Dimargaritales, Harpellales, Kickxellales) as well as four genera previously placed within two of these orders (Barbatospora, Orphella, Ramicandelaber, Spiromyces). Dimargaritales and Ramicandelaber are the earliest diverging members of the subphylum, although the relationship between these taxa remains uncertain. The remaining six clades form a monophyletic group, with Barbatospora diverging first. The next split divides the remaining members of the subphylum into two subclades: (i) Asellariales and Harpellales and (ii) Kickxellales, Orphella and Spiromyces. Estimation of ancestral states for four potentially informative morphological and ecological characters reveals that arthropod endosymbiosis might have been an important factor in the early evolution of the Kickxellomycotina.

ASSESSING THE POTENTIAL EFFECTS OF FUNGICIDES ON NONTARGET GUT FUNGI (TRICHOMYCETES) AND THEIR ASSOCIATED LARVAL BLACK FLY HOSTS.

Fungicides are moderately hydrophobic and have been detected in water and sediment, particularly in agricultural watersheds, but typically are not included in routine water quality monitoring efforts. This is despite their widespread use and frequent application to combat fungal pathogens. Whereas the efficacy of these compounds on fungal pathogens is well documented, little is known about their effects on nontarget fungi. This pilot study, a field survey in southwestern Idaho from April to December 2010 on four streams with varying pesticide inputs (two agricultural and two reference sites), was conducted to assess nontarget impact of fungicides on gut fungi, or trichomycetes. Tissues of larval black flies (Diptera: Simuliidae), hosts of gut fungi, were analyzed for pesticide accumulation. Fungicides were detected in hosts from streams within agricultural watersheds but were not detected in hosts from reference streams. Gut fungi from agricultural sites exhibited decreased percent infestation, density within the gut, and sporulation, and black fly tissues had elevated pesticide concentrations. Differences observed between the sites demonstrate a potential effect on this symbiotic system. Future research is needed to parse out the details of the complex biotic and abiotic relationships; however, these preliminary results indicate that impacts to nontarget organisms could have far-reaching consequences within aquatic ecosystems.

Discovery of small molecules targeting the tandem tudor domain of the epigenetic factor UHRF1 using fragment-based ligand discovery.

Despite the established roles of the epigenetic factor UHRF1 in oncogenesis, no UHRF1-targeting therapeutics have been reported to date. In this study, we use fragment-based ligand discovery to identify novel scaffolds for targeting the isolated UHRF1 tandem Tudor domain (TTD), which recognizes the heterochromatin-associated histone mark H3K9me3 and supports intramolecular contacts with other regions of UHRF1. Using both binding-based and function-based screens of a ~ 2300-fragment library in parallel, we identified 2,4-lutidine as a hit for follow-up NMR and X-ray crystallography studies. Unlike previous reported ligands, 2,4-lutidine binds to two binding pockets that are in close proximity on TTD and so has the potential to be evolved into more potent inhibitors using a fragment-linking strategy. Our study provides a useful starting point for developing potent chemical probes against UHRF1.

The orphan nuclear receptor TLX: an emerging master regulator of cross-talk between microglia and neural precursor cells.

Neuroinflammation and neurogenesis have both been the subject of intensive investigation over the past 20 years. The sheer complexity of their regulation and their ubiquity in various states of health and disease have sometimes obscured the progress that has been made in unraveling their mechanisms and regulation. A recent study by Kozareva et al. (Neuronal Signaling (2019) 3), provides evidence that the orphan nuclear receptor TLX is central to communication between microglia and neural precursor cells and could help us understand how inflammation, mediated by microglia, influences the development of new neurons in the adult hippocampus. Here, we put recent studies on TLX into the context of what is known about adult neurogenesis and microglial activation in the brain, along with the many hints that these processes must be inter-related.

A new species of Ephemerellomyces from North America highlights its morphological plasticity and possible intergeneric similarities with other Harpellales.

During routine bioprospecting efforts in southern Idaho, we recovered a new species, Ephemerellomyces kandelii from nymphs of the mayfly genus Ephemerella (Ephemerellidae) in Dry Creek drainage, near Boise. This is the second observation of this monotypic genus since the description of Ephemerellomyces aquilonius from Norway in 2004. Ephemerellomyces was described partly on the basis of unusual developmental features at the base of the thallus. Specifically, trichospores were noted with the capacity to germinate, attach to the hindgut cuticle of the mayfly host, and produce a cell bearing a single terminal trichospore. This feature was less prominent yet noted in our collections from Idaho, but we argue that the remnant basal cell may also be a morphological feature that unites the genus and deserves further scrutinization across closely related taxa. Compared to the two Norwegian surveys, our collections extended over 1 y, a timeframe that was critical to capture the extent of the natural morphological range and plasticity of E. kandelii. Specifically, we emend the generic description to accommodate the first observation of zygospores (Type II) and E. kandelii is described with dimorphic trichospores, yet another genus of the Harpellales to include species with this feature. We also document some variability in trichospore dimensions with E. kandelii, following routine procedures, in vitro slide incubations and staining; these are discussed in light of prior reports noting morphological changes in asexual spores of certain Harpellales following such handling. Finally, we extend our discussion to include putatively closely related taxa of gut fungi in other Ephemeroptera.