Shrews as reservoir hosts of borna disease virus.
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Borna disease virus (BDV) is the causative agent of severe T-cell-mediated meningoencephalitis in horses, sheep, and other animal species in central Europe. Here we report the first unequivocal detection of a BDV reservoir species, the bicolored white-toothed shrew, Crocidura leucodon, in an area in Switzerland with endemic Borna disease. (+info)
Neuroanatomical evidence for segregation of nerve fibers conveying light touch and pain sensation in Eimer's organ of the mole.
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Talpid moles are small insectivores that live in dark underground tunnels. They depend heavily on touch to navigate and find food. Most species have an array of complex epidermal sensory structures called Eimer's organs that cover the tip of the nose. In this study, the anatomy of Eimer's organ was examined in the coast mole and star-nosed mole by using the fluorescent styryl pyridinium dye AM1-43 and immunocytochemical staining for neurofilament 200 and substance P. In addition, DiI was used to label neural components of Eimer's organ. AM1-43 labeled all of the Eimer's organ receptors after systemic injection, suggesting a role in mechanotransduction. Immunostaining with neurofilament 200 and substance P labeled distinct subtypes of sensory fibers. Substance P labeled a group of free nerve endings along the outer edge of Eimer's organ, indicating a nociceptive role for these fibers. In contrast, neurofilament 200 labeled a more central set of nerve endings, suggesting that these fibers function as low-threshold mechanoreceptors. By labeling subsets of trigeminal afferents distant from the receptor array with DiI, we revealed innervation patterns indicating that one afferent supplies the outer, substance P-positive set of free nerve endings, whereas several afferents differentially innervate the central free nerve endings. Our results suggest that the free nerve endings innervating Eimer's organ are largely mechanosensitive and may play an important role in the rapid sensory discrimination observed in these species. (+info)
Response properties of primary afferents supplying Eimer's organ.
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The mole's nose is covered with mechanosensory structures called Eimer's organs. Each organ contains Merkel cell-neurite complexes, Paciniform corpuscles and intraepidermal free nerve endings. The function of Eimer's organ has been the subject of speculation since the 1800s, but responses from the afferents have never been investigated. Our goal was to explore the function of Eimer's organ by recording primary afferent responses to a range of mechanosensory stimuli. Unit activity from the trigeminal ganglion was recorded from coast (Scapanus orarius) and star-nosed (Condylura cristata) moles, while stimulating the nose with a Chubbuck mechanosensory stimulator, a piezo-electric sweeping stimulator, and hand-held probes. Stimuli included static indentations, sinusoidal displacements, different indentation velocities, displacement amplitudes, and directional stimuli across the skin. Receptive fields were small, sometimes restricted to single Eimer's organs. Responses were consistent with a slowly adapting Merkel cell-neurite complex-like receptor class and a dynamically sensitive Pacinian-like rapidly adapting class. A second rapidly adapting class was hypothesized to represent activity of prominent free nerve endings within a central cell column. Some receptors were most sensitive to stimuli applied in particular directions across the skin. Most receptors relayed mechanosensory input with high temporal fidelity. In addition some receptors were tuned to respond best when stimulated at a velocity matching the velocity of the nose during foraging. These results support the hypothesis that Eimer's organ functions to detect small surface features and textures by encoding and integrating deflection information for multiple Eimer's organs during brief touches. (+info)
Fine structure of Eimer's organ in the coast mole (Scapanus orarius).
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Eimer's organ is a small, densely innervated sensory structure found on the glabrous rhinarium of most talpid moles. This structure consists of an epidermal papilla containing a central circular column of cells associated with intraepidermal free nerve endings, Merkel cell neurite complexes, and lamellated corpuscles. The free nerve endings within the central cell column form a ring invested in the margins of the column, surrounding 1-2 fibers that pass through the center of the column. A group of small-diameter nociceptive free nerve endings that are immunoreactive for substance P surrounds this central ring of larger-diameter free nerve endings. Transmission electron microscopy revealed a high concentration of tonofibrils in the epidermal cells of the central column, suggesting they are more rigid than the surrounding keratinocytes and may play a mechanical role in transducing stimuli to the different receptor terminals. The intraepidermal free nerve endings within the central column begin to degrade 15 microm from the base of the stratum corneum and do not appear to be active within the keratinized outer layer. The peripheral free nerve endings are structurally distinct from their counterparts in the central column and immunocytochemical double labeling with myelin basic protein and substance P indicates these afferents are unmyelinated. Merkel cell-neurite complexes and lamellated corpuscles are similar in morphology to those found in a range of other mammalian skin. (+info)
A cross-species comparison of X-chromosome inactivation in Eutheria.
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Mammalian X-chromosome inactivation achieves dosage compensation between the sexes by the silencing of one X chromosome in females. In Eutheria, X inactivation is initiated by the large noncoding RNA Xist; however, it is unknown how this RNA results in silencing of the chromosome or why, at least in humans, many genes escape silencing in somatic cells. We have sequenced the coast mole Xist gene and compared the Xist RNA sequence among seven eutherians to provide insight into the structure of the RNA and origins of the gene. Using DNA methylation of promoter sequences to assess whether genes are silenced in females we report the inactivation status of seven X-linked genes in humans and mice as well as two additional eutherians, the mole and the cow, providing evidence that escape from inactivation is common among Eutheria. (+info)
Chromosomal instability in Afrotheria: fragile sites, evolutionary breakpoints and phylogenetic inference from genome sequence assemblies.
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BACKGROUND: Extant placental mammals are divided into four major clades (Laurasiatheria, Supraprimates, Xenarthra and Afrotheria). Given that Afrotheria is generally thought to root the eutherian tree in phylogenetic analysis of large nuclear gene data sets, the study of the organization of the genomes of afrotherian species provides new insights into the dynamics of mammalian chromosomal evolution. Here we test if there are chromosomal bands with a high tendency to break and reorganize in Afrotheria, and by analyzing the expression of aphidicolin-induced common fragile sites in three afrotherian species, whether these are coincidental with recognized evolutionary breakpoints. RESULTS: We described 29 fragile sites in the aardvark (OAF) genome, 27 in the golden mole (CAS), and 35 in the elephant-shrew (EED) genome. We show that fragile sites are conserved among afrotherian species and these are correlated with evolutionary breakpoints when compared to the human (HSA) genome. Inddition, by computationally scanning the newly released opossum (Monodelphis domestica) and chicken sequence assemblies for use as outgroups to Placentalia, we validate the HSA 3/21/5 chromosomal synteny as a rare genomic change that defines the monophyly of this ancient African clade of mammals. On the other hand, support for HSA 1/19p, which is also thought to underpin Afrotheria, is currently ambiguous. CONCLUSION: We provide evidence that (i) the evolutionary breakpoints that characterise human syntenies detected in the basal Afrotheria correspond at the chromosomal band level with fragile sites, (ii) that HSA 3p/21 was in the amniote ancestor (i.e., common to turtles, lepidosaurs, crocodilians, birds and mammals) and was subsequently disrupted in the lineage leading to marsupials. Its expansion to include HSA 5 in Afrotheria is unique and (iii) that its fragmentation to HSA 3p/21 + HSA 5/21 in elephant and manatee was due to a fission within HSA 21 that is probably shared by all Paenungulata. (+info)
Cone photoreceptors and potential UV vision in a subterranean insectivore, the European mole.
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