Cellular mechanics of germ band retraction in Drosophila

Germ band retraction involves a dramatic rearrangement of the tissues on the surface of the Drosophila embryo. As germ band retraction commences, one tissue, the germ band, wraps around another, the amnioserosa. Through retraction the two tissues move cohesively as the highly elongated cells of the amnioserosa contract and the germ band moves so it is only on one side of the embryo. To understand the mechanical drivers of this process, we designed a series of laser ablations that suggest a mechanical role for the amnioserosa. First, we find that during mid retraction, segments in the curve of the germ band are under anisotropic tension. The largest tensions are in the direction in which the amnioserosa contracts. Second, ablating one lateral flank of the amnioserosa reduces the observed force anisotropy and leads to retraction failures. The other intact flank of amnioserosa is insufficient to drive retraction, but can support some germ band cell elongation and is thus not a full phenocopy of ush mutants. Another ablation-induced failure in retraction can phenocopy mys mutants, and does so by targeting amnioserosa cells in the same region where the mutant fails to adhere to the germ band. We conclude that the amnioserosa must play a key, but assistive, mechanical role that aids uncurling of the germ band.     

Emx2 and early hair cell development in the mouse inner ear

Emx2 is a homeodomain protein that plays a critical role in inner ear development. Homozygous null mice die at birth with a range of defects in the CNS, renal system and skeleton. The cochlea is shorter than normal with about 60% fewer auditory hair cells. It appears to lack outer hair cells and some supporting cells are either absent or fail to differentiate. Many of the hair cells differentiate in pairs and although their hair bundles develop normally their planar cell polarity is compromised. Measurements of cell polarity suggest that classic planar cell polarity molecules are not directly influenced by Emx2 and that polarity is compromised by developmental defects in the sensory precursor population or by defects in epithelial cues for cell alignment. Planar cell polarity is normal in the vestibular epithelia although polarity reversal across the striola is absent in both the utricular and saccular maculae. In contrast, cochlear hair cell polarity is disorganized. The expression domain for Bmp4 is expanded and Fgfr1 and Prox1 are expressed in fewer cells in the cochlear sensory epithelium of Emx2 null mice. We conclude that Emx2 regulates early developmental events that balance cell proliferation and differentiation in the sensory precursor population.     

Non-native grasses reduce scaled quail habitat

Non-native grasses are frequently sown in the southwestern United States for livestock forage and erosion control. These grasses often spread from areas where they are planted and replace native grasses and forbs. We tested the hypothesis that chestnut-bellied scaled quail (Callipepla squamata castanogastris) avoid locations dominated by non-native grasses. We trapped scaled quail at 5 different sites in southern Texas, USA, and located quail fitted with necklace-style transmitters 3 times/week during 2013–2014. We manually delineated plant communities using aerial maps and on-the-ground knowledge of the study sites. We examined second-order (home-range scale) selection by comparing proportion of the areas of plant communities within 62 scaled quail home ranges (used) paired with random home ranges (available). We examined third-order (within-home-range scale) selection by comparing the composition of bird location (used) and random (available) points based on proportion of points within plant communities. For both home-range scale and within-home-range scale analyses, we used non-parametric multivariate analysis of variance with 9,999 random permutations. We examined fourth-order (organism-centered) selection by measuring vegetation variables at used and available locations and then estimating the relative probability of use of vegetation variables and by estimating continuous selection functions for variables that were influential in determining relative probability of use. Buffelgrass (Pennisetum ciliare) and Old World bluestems (Bothriochloa spp., Dichanthium annulatum and other Dichanthium spp.) comprised 99% (95% CI = 98–100%, n = 143 sites where non-native plants occurred) of the non-native grasses in our study areas. Scaled quail avoided non-native and riparian plant communities at the home-range and within-home-range scales of selection. At the organism-centered scale of selection, odds of use by scaled quail decreased 28% for every 10% increase in non-native grass cover and increased 12% for every 10% increase in shrub canopy cover. Scaled quail avoided locations with >10% canopy cover of non-native grasses. Based on avoidance at 3 scales of selection, dominance of buffelgrass and Old World bluestems degrades habitat for scaled quail. Spread and sowing of non-native grasses and brush clearing may be partly responsible for declines in scaled quail populations. © 2019 The Wildlife Society.     

Specificity and actions of an arylaspartate inhibitor of glutamate transport at the Schaffer collateral-CA1 pyramidal cell synapse

In this study we characterized the pharmacological selectivity and physiological actions of a new arylaspartate glutamate transporter blocker, L-threo-ß-benzylaspartate (L-TBA). At concentrations up to 100 µM, L-TBA did not act as an AMPA receptor (AMPAR) or NMDA receptor (NMDAR) agonist or antagonist when applied to outside-out patches from mouse hippocampal CA1 pyramidal neurons. L-TBA had no effect on the amplitude of field excitatory postsynaptic potentials (fEPSPs) recorded at the Schaffer collateral-CA1 pyramidal cell synapse. Excitatory postsynaptic currents (EPSCs) in CA1 pyramidal neurons were unaffected by L-TBA in the presence of physiological extracellular Mg²⁺ concentrations, but in Mg²⁺-free solution, EPSCs were significantly prolonged as a consequence of increased NMDAR activity. Although L-TBA exhibited approximately four-fold selectivity for neuronal EAAT3 over glial EAAT1/EAAT2 transporter subtypes expressed in Xenopus oocytes, the L-TBA concentration-dependence of the EPSC charge transfer increase in the absence of Mg²⁺ was the same in hippocampal slices from EAAT3 +/+ and EAAT3 −/− mice, suggesting that TBA effects were primarily due to block of glial transporters. Consistent with this, L-TBA blocked synaptically evoked transporter currents in CA1 astrocytes with a potency in accord with its block of heterologously expressed glial transporters. Extracellular recording in the presence of physiological Mg²⁺ revealed that L-TBA prolonged fEPSPs in a frequency-dependent manner by selectively increasing the NMDAR-mediated component of the fEPSP during short bursts of activity. The data indicate that glial glutamate transporters play a dominant role in limiting extrasynaptic transmitter diffusion and binding to NMDARs. Furthermore, NMDAR signaling is primarily limited by voltage-dependent Mg²⁺ block during low-frequency activity, while the relative contribution of transport increases during short bursts of higher frequency signaling.     

Growth and survival rates of dispersing free embryos and settled larvae of pallid sturgeon (Scaphirhynchus albus) in the Missouri River,Montana and North Dakota

Environmental Biology of Fishes - We released nearly 1.0 million 1-day post-hatch (dph) and 5-dph pallid sturgeon (Scaphirhynchus albus) free embryos in the Missouri River on 1 July 2019 and...     

Neuropathology in mouse models of mucopolysaccharidosis type I, IIIA and IIIB

Mucopolysaccharide diseases (MPS) are caused by deficiency of glycosaminoglycan (GAG) degrading enzymes, leading to GAG accumulation. Neurodegenerative MPS diseases exhibit cognitive decline, behavioural problems and shortened lifespan. We have characterised neuropathological changes in mouse models of MPSI, IIIA and IIIB to provide a better understanding of these events.Wild-type (WT), MPSI, IIIA and IIIB mouse brains were analysed at 4 and 9 months of age. Quantitative immunohistochemistry showed significantly increased lysosomal compartment, GM2 ganglioside storage, neuroinflammation, decreased and mislocalised synaptic vesicle associated membrane protein, (VAMP2), and decreased post-synaptic protein, Homer-1, in layers II/III-VI of the primary motor, somatosensory and parietal cortex. Total heparan sulphate (HS), was significantly elevated, and abnormally N-, 6-O and 2-O sulphated compared to WT, potentially altering HS-dependent cellular functions. Neuroinflammation was confirmed by significantly increased MCP-1, MIP-1α, IL-1α, using cytometric bead arrays. An overall genotype effect was seen in all parameters tested except for synaptophysin staining, neuronal cell number and cortical thickness which were not significantly different from WT. MPSIIIA and IIIB showed significantly more pronounced pathology than MPSI in lysosomal storage, astrocytosis, microgliosis and the percentage of 2-O sulphation of HS. We also observed significant time progression of all genotypes from 4-9 months in lysosomal storage, astrocytosis, microgliosis and synaptic disorganisation but not GM2 gangliosidosis. Individual genotype*time differences were disparate, with significant progression from 4 to 9 months only seen for MPSIIIB with lysosomal storage, MPSI with astrocytocis and MPSIIIA with microgliosis as well as neuronal loss. Transmission electron microscopy of MPS brains revealed dystrophic axons, axonal storage, and extensive lipid and lysosomal storage. These data lend novel insight to MPS neuropathology, suggesting that MPSIIIA and IIIB have more pronounced neuropathology than MPSI, yet all are still progressive, at least in some aspects of neuropathology, from 4-9 months.     

Cell cycle progression is required for zebrafish somite morphogenesis but not segmentation clock function

Cell division, differentiation and morphogenesis are coordinated during embryonic development, and frequently are in disarray in pathologies such as cancer. Here, we present a zebrafish mutant that ceases mitosis at the beginning of gastrulation, but that undergoes axis elongation and develops blood, muscle and a beating heart. We identify the mutation as being in early mitotic inhibitor 1 (emi1), a negative regulator of the Anaphase Promoting Complex, and use the mutant to examine the role of the cell cycle in somitogenesis. The mutant phenotype indicates that axis elongation during the segmentation period is driven substantially by cell migration. We find that the segmentation clock, which regulates somitogenesis, functions normally in the absence of cell cycle progression, and observe that mitosis is a modest source of noise for the clock. Somite morphogenesis involves the epithelialization of the somite border cells around a core of mesenchyme. As in wild-type embryos, somite boundary cells are polarized along a Fibronectin matrix in emi1(-/-). The mutants also display evidence of segment polarity. However, in the absence of a normal cell cycle, somites appear to hyper-epithelialize, as the internal mesenchymal cells exit the core of the somite after initial boundary formation. Thus, cell cycle progression is not required during the segmentation period for segmentation clock function but is necessary for the normal segmental arrangement of epithelial borders and internal mesenchymal cells.