Wnt/β-catenin dependent cell proliferation underlies segmented lateral line morphogenesis

Morphogenesis is a fascinating but complex and incompletely understood developmental process. The sensory lateral line system consists of only a few hundred cells and is experimentally accessible making it an excellent model system to interrogate the cellular and molecular mechanisms underlying segmental morphogenesis. The posterior lateral line primordium periodically deposits prosensory organs as it migrates to the tail tip. We demonstrate that periodic proneuromast deposition is governed by a fundamentally different developmental mechanism than the classical models of developmental periodicity represented by vertebrate somitogenesis and early Drosophila development. Our analysis demonstrates that proneuromast deposition is driven by periodic lengthening of the primordium and a stable Wnt/β-catenin activation domain in the leading region of the primordium. The periodic lengthening of the primordium is controlled by Wnt/β-catenin/Fgf-dependent proliferation. Once proneuromasts are displaced into the trailing Wnt/β-catenin-free zone they are deposited. We have previously shown that Wnt/β-catenin signaling induces Fgf signaling and that interactions between these two pathways regulate primordium migration and prosensory organ formation. Therefore, by coordinating migration, prosensory organ formation and proliferation, localized activation of Wnt/β-catenin signaling in the leading zone of the primordium plays a crucial role in orchestrating lateral line morphogenesis.     

Demographic Amplification of Climate Change Experienced by the Contiguous United States Population during the 20th Century

Better understanding of the changing relationship between human populations and climate is a global research priority. The 20^th century in the contiguous United States offers a particularly well-documented example of human demographic expansion during a period of radical socioeconomic and environmental change. One would expect that as human society has been transformed by technology, we would become increasingly decoupled from climate and more dependent on social infrastructure. Here we use spatially-explicit models to evaluate climatic, socio-economic and biophysical correlates of demographic change in the contiguous United States between 1900 and 2000. Climate-correlated variation in population growth has caused the U.S. population to shift its realized climate niche from cool, seasonal climates to warm, aseasonal climates. As a result, the average annual temperature experienced by U.S. citizens between 1920 and 2000 has increased by more than 1.5°C and the temperature seasonality has decreased by 1.1°C during a century when climate change accounted for only a 0.24°C increase in average annual temperature and a 0.15°C decrease in temperature seasonality. Thus, despite advancing technology, climate-correlated demographics continue to be a major feature of contemporary U.S. society. Unfortunately, these demographic patterns are contributing to a substantial warming of the climate niche during a period of rapid environmental warming, making an already bad situation worse.     

Distinct edaphic habitats are occupied by discrete legume assemblages with unique indicator species in the Cape Peninsula of South Africa

Aims The Cape Peninsula is a small area (471 km 2) situated on the south-westernmost tip of the Core Cape Subregion (CCR) of South Africa. Within the Cape Peninsula, Fabaceae are the third most species-rich plant family (162 species) and they have the second highest number of endemic species after the Ericaceae. However, legumes are not the dominant taxa in the vegetation. They tend to show patchy distributions within the landscape and different species assemblages usually occupy particular niches at any given locality. The present study undertook to establish if edaphic factors influence legume species distribution in the Cape Peninsula and to determine the key indicator species for the different assemblages.Methods Soils from 27 legume sites, spanning all major geological substrates of the Cape Peninsula, were analysed for 31 chemical and physical properties. Legume species present at each site were recorded and a presence/absence matrix was generated. Cluster analysis and discriminant function analysis (DFA) were run to group the sites based on overall similarity in edaphic characteristics and to identify the soil parameters contributing towards discriminating the groups. Canonical correspondence analysis (CCA) was used to test for a correlation between legume species compositions and edaphic factors. The strength of the association between legume species and site groupings based on edaphic properties was assessed using indicator species analysis.Important findings Based on similarity in overall soil characteristics, the sites formed three clusters: one comprising sites of sandstone geology, one with dune sand sites and the third cluster comprising sites of both shale and granite geologies (hereafter referred to as soil types). The DFA confirmed the distinctness of these clusters and the CCA showed a significant correlation between legume species composition and edaphic factors. The key edaphic parameters were clay content, iron (Fe), potassium (K), sulphur (S) and zinc (Zn). These findings reveal that the Cape Peninsula is edaphically heterogeneous and edaphically distinct habitats contain discrete legume species assemblages that can be distinguished by unique indicator species. Furthermore, multiple soil parameters, rather than a single parameter, are involved. Therefore, edaphic factors play a significant role in driving the distribution of legume species in the Cape Peninsula and discrete legume species assemblages occupy distinct habitats.     

A Time Course Analysis of the Electrophysiological Properties of Neurons Differentiated from Human Induced Pluripotent Stem Cells (iPSCs)

Many protocols have been designed to differentiate human embryonic stem cells (ESCs) and human induced pluripotent stem cells (iPSCs) into neurons. Despite the relevance of electrophysiological properties for proper neuronal function, little is known about the evolution over time of important neuronal electrophysiological parameters in iPSC-derived neurons. Yet, understanding the development of basic electrophysiological characteristics of iPSC-derived neurons is critical for evaluating their usefulness in basic and translational research. Therefore, we analyzed the basic electrophysiological parameters of forebrain neurons differentiated from human iPSCs, from day 31 to day 55 after the initiation of neuronal differentiation. We assayed the developmental progression of various properties, including resting membrane potential, action potential, sodium and potassium channel currents, somatic calcium transients and synaptic activity. During the maturation of iPSC-derived neurons, the resting membrane potential became more negative, the expression of voltage-gated sodium channels increased, the membrane became capable of generating action potentials following adequate depolarization and, at day 48–55, 50% of the cells were capable of firing action potentials in response to a prolonged depolarizing current step, of which 30% produced multiple action potentials. The percentage of cells exhibiting miniature excitatory post-synaptic currents increased over time with a significant increase in their frequency and amplitude. These changes were associated with an increase of Ca²⁺ transient frequency. Co-culturing iPSC-derived neurons with mouse glial cells enhanced the development of electrophysiological parameters as compared to pure iPSC-derived neuronal cultures. This study demonstrates the importance of properly evaluating the electrophysiological status of the newly generated neurons when using stem cell technology, as electrophysiological properties of iPSC-derived neurons mature over time.     

Structure and activity of AbiQ,a lactococcal endoribonuclease belonging to the type III toxin–antitoxin system

AbiQ is a phage resistance mechanism found on a native plasmid of Lactococcus lactis that abort virulent phage infections. In this study, we experimentally demonstrate that AbiQ belongs to the recently described type III toxin–antitoxin systems. When overexpressed, the AbiQ protein (ABIQ) is toxic and causes bacterial death in a bacteriostatic manner. Northern and Western blot experiments revealed that the abiQ gene is transcribed and translated constitutively, and its expression is not activated by a phage product. ABIQ is an endoribonuclease that specifically cleaves its cognate antitoxin RNA molecule in vivo. The crystal structure of ABIQ was solved and site‐directed mutagenesis identified key amino acids for its anti‐phage and/or its RNase function. The AbiQ system is the first lactococcal abortive infection system characterized to date at a structural level.     

Microcalorimetry as a diagnostic and analytical tool for the assessment of biodegradation of 2,4-D in a liquid medium and in soil

The biodegradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) byPseudomonas cepacia was assessed by microcalorimetry in a liquid medium and in sterilized soil at 25°C under aerobic conditions. It was found that thermograms of the rate of heat evolved versus time (dQ/dt versust) can be used as a diagnostic tool to identify the timet ₁ required for the primary biodegradation of 2,4-D and the timet _f required for the completion of the biodegradation activity in a liquid medium as well as in soil. Microcalorimetry can also be used as an analytical tool to monitor the progress of 2,4-D consumption during the biodegradation process in a liquid medium and to measure the importance of the soil sorption/desorption of intermediate metabolites. A new concept called bioeffort was defined as the product of the biodegradation time (t) and the biomass concentration (X) at that time. This concept was used to predict either the biomass concentration required or the duration of the primary biodegradation of 2,4-D in soil from the data obtained from a liquid medium.