Developmental cues and persistent neurogenic potential within an in vitro neural niche

<p>Abstract</p> <p>Background</p> <p>Neurogenesis, the production of neural cell-types from neural stem cells (NSCs), occurs during development as well as within select regions of the adult brain. NSCs in the adult subependymal zone (SEZ) exist in a well-categorized niche microenvironment established by surrounding cells and their molecular products. The components of this niche maintain the NSCs and their definitive properties, including the ability to self-renew and multipotency (neuronal and glial differentiation).</p> <p>Results</p> <p>We describe a model <it>in vitro </it>NSC niche, derived from embryonic stem cells, that produces many of the cells and products of the developing subventricular zone (SVZ) and adult SEZ NSC niche. We demonstrate a possible role for apoptosis and for components of the extracellular matrix in the maintenance of the NSC population within our niche cultures. We characterize expression of genes relevant to NSC self-renewal and the process of neurogenesis and compare these findings to gene expression produced by an established neural-induction protocol employing retinoic acid.</p> <p>Conclusions</p> <p>The <it>in vitro </it>NSC niche shows an identity that is distinct from the neurally induced embryonic cells that were used to derive it. Molecular and cellular components found in our <it>in vitro </it>NSC niche include NSCs, neural progeny, and ECM components and their receptors. Establishment of the <it>in vitro </it>NSC niche occurs in conjunction with apoptosis. Applications of this culture system range from studies of signaling events fundamental to niche formation and maintenance as well as development of unique NSC transplant platforms to treat disease or injury.</p

Molecular phylogeography of the troglobiotic millipede Tetracion Hoffman, 1956 (Diplopoda, Callipodida, Abacionidae)

More than 85 species of cave-obligate (troglobiotic) millipede have been described from North America. Understanding the patterns and processes that determine their distribution in this region is an area of recent research. Here, we present the first molecular phylogeographic study of troglobiotic millipedes. Millipedes of the genus Tetracion Hoffman, 1956 (Callipodida: Abacionidae) inhabit caves on the Cumberland Plateau in Tennessee and Alabama, a global hotspot for cave biodiversity. Three species have been described: T. jonesi Hoffman, 1956, T. antraeum Hoffman, 1956, and T. tennesseensis Causey, 1959. To examine genetic divergence within and between species of Tetracion we sequenced part of the mitochondrial cytochrome oxidase 1 gene from 53 individuals from eleven caves across the range of T. tennesseensis and in the northern part of the range of T. jonesi. We found: (1) little variation within species (six haplotypes in T. tennesseensis and four haplotypes in T. jonesi, with a maximum of 1.4% intraspecific divergence between haplotypes), (2) that gene flow between caves is limited (7 of 10 haplotypes were restricted to a single cave, and FST > 0.80 and P < 0.05 for fifteen of eighteen comparisons between caves), and (3) significant genetic divergence between species (8.8% between T. tennesseensis and T. jonesi). Our results are consistent with previous morphology-based species definitions showing T. tennesseensis and T. jonesi belonging to distinct taxa. Our research contributes to the growing body of phylogeographic information about cave species on the Cumberland Plateau, and provides a point of comparison for future studies of troglobionts and millipedes

Patterns of Cave Biodiversity and Endemism in the Appalachians and Interior Plateau of Tennessee, USA

Using species distribution data, we developed a georeferenced database of troglobionts (cave-obligate species) in Tennessee to examine spatial patterns of species richness and endemism, including \u3e2000 records for 200 described species. Forty aquatic troglobionts (stygobionts) and 160 terrestrial troglobionts are known from caves in Tennessee, the latter having the greatest diversity of any state in the United States. Endemism was high, with 25% of terrestrial troglobionts (40 species) and 20% of stygobionts (eight species) known from just a single cave and nearly two-thirds of all troglobionts (130 species) known from five or fewer caves. Species richness and endemism were greatest in the Interior Plateau (IP) and Southwestern Appalachians (SWA) ecoregions, which were twice as diverse as the Ridge and Valley (RV). Troglobiont species assemblages were most similar between the IP and SWA, which shared 59 species, whereas the RV cave fauna was largely distinct. We identified a hotspot of cave biodiversity with a center along the escarpment of the Cumberland Plateau in south-central Tennessee defined by both species richness and endemism that is contiguous with a previously defined hotspot in northeastern Alabama. Nearly half (91 species) of Tennessee’s troglobiont diversity occurs in this region where several cave systems contain ten or more troglobionts, including one with 23 species. In addition, we identified distinct troglobiont communities across the state. These communities corresponded to hydrological boundaries and likely reflect past or current connectivity between subterranean habitats within and barriers between hydrological basins. Although diverse, Tennessee’s subterranean fauna remains poorly studied and many additional species await discovery and description. We identified several undersampled regions and outlined conservation and management priorities to improve our knowledge and aid in protection of the subterranean biodiversity in Tennessee

Patterns of Cave Biodiversity and Endemism in the Appalachians and Interior Plateau of Tennessee, USA

Using species distribution data, we developed a georeferenced database of troglobionts (cave-obligate species) in Tennessee to examine spatial patterns of species richness and endemism, including \u3e2000 records for 200 described species. Forty aquatic troglobionts (stygobionts) and 160 terrestrial troglobionts are known from caves in Tennessee, the latter having the greatest diversity of any state in the United States. Endemism was high, with 25% of terrestrial troglobionts (40 species) and 20% of stygobionts (eight species) known from just a single cave and nearly two-thirds of all troglobionts (130 species) known from five or fewer caves. Species richness and endemism were greatest in the Interior Plateau (IP) and Southwestern Appalachians (SWA) ecoregions, which were twice as diverse as the Ridge and Valley (RV). Troglobiont species assemblages were most similar between the IP and SWA, which shared 59 species, whereas the RV cave fauna was largely distinct. We identified a hotspot of cave biodiversity with a center along the escarpment of the Cumberland Plateau in south-central Tennessee defined by both species richness and endemism that is contiguous with a previously defined hotspot in northeastern Alabama. Nearly half (91 species) of Tennessee’s troglobiont diversity occurs in this region where several cave systems contain ten or more troglobionts, including one with 23 species. In addition, we identified distinct troglobiont communities across the state. These communities corresponded to hydrological boundaries and likely reflect past or current connectivity between subterranean habitats within and barriers between hydrological basins. Although diverse, Tennessee’s subterranean fauna remains poorly studied and many additional species await discovery and description. We identified several undersampled regions and outlined conservation and management priorities to improve our knowledge and aid in protection of the subterranean biodiversity in Tennessee

Caves as islands: mitochondrial phylogeography of the cave-obligate spider species Nesticus barri (Araneae: Nesticidae)

Volume: 38Start Page: 49End Page: 5

Mitochondrial sequence data indicate “Vicariance by Erosion” as a mechanism of species diversification in North American Ptomaphagus (Coleoptera, Leiodidae, Cholevinae) cave beetles

Small carrion beetles (Coleoptera: Leiodidae: Cholevinae) are members of cave communities around the world and important models for understanding the colonization of caves, adaptation to cave life, and the diversification of cave-adapted lineages. We developed a molecular phylogeny to examine the diversification of the hirtus-group of the small carrion beetle genus Ptomaphagus. The hirtus-group has no surface-dwelling members; it consists of 19 short-range endemic cave- and soil-dwelling species in the central and southeastern United States of America. Taxonomic, phylogenetic and biogeographic data were previously interpreted to suggest the hirtus-group diversified within the past 350,000 years through a series of cave colonization and speciation events related to Pleistocene climate fluctuations. However, our time-calibrated molecular phylogeny resulting from the analysis of 2,300 nucleotides from five genes across three mitochondrial regions (cox1, cytb, rrnL-trnL-nad1) for all members of the clade paints a different picture. We identify three stages of diversification in the hirtus-group: (1) ~10 million years ago (mya), the lineage that develops into P. shapardi, a soil-dwelling species from the Ozarks, diverged from the lineage that gives rise to the 18 cave-obligate members of the group; (2) between 8.5 mya and 6 mya, seven geographically distinct lineages diverged across Kentucky, Tennessee, Alabama and Georgia; six of these lineages represent a single species today, whereas (3) the ‘South Cumberlands’ lineage in Tennessee and Alabama diversified into 12 species over the past ~6 my. While the events triggering diversification during the first two stages remain to be determined, the distributions, phylogenetic relationships and divergence times in the South Cumberlands lineage are consistent with populations being isolated by vicariant events as the southern Cumberland Plateau eroded and fragmented over millions of years