Hoxa2 knockdown in Xenopus results in hyoid to mandibular homeosis.

The skeletal structures of the face and throat are derived from cranial neural crest cells (NCCs) that migrate from the embryonic neural tube into a series of branchial arches (BAs). The first arch (BA1) gives rise to the upper and lower jaw cartilages, whereas hyoid structures are generated from the second arch (BA2). The Hox paralogue group 2 (PG2) genes, Hoxa2 and Hoxb2, show distinct roles for hyoid patterning in tetrapods and fishes. In the mouse, Hoxa2 acts as a selector of hyoid identity, while its paralogue Hoxb2 is not required. On the contrary, in zebrafish Hoxa2 and Hoxb2 are functionally redundant for hyoid arch patterning. Here, we show that in Xenopus embryos morpholino-induced functional knockdown of Hoxa2 is sufficient to induce homeotic changes of the second arch cartilage. Moreover, Hoxb2 is downregulated in the BA2 of Xenopus embryos, even though initially expressed in second arch NCCs, similar to mouse and unlike in zebrafish. Finally, Xbap, a gene involved in jaw joint formation, is selectively upregulated in the BA2 of Hoxa2 knocked-down frog embryos, supporting a hyoid to mandibular change of NCC identity. Thus, in Xenopus Hoxa2 does not act redundantly with Hoxb2 for BA2 patterning, similar to mouse and unlike in fish. These data bring novel insights into the regulation of Hox PG2 genes and hyoid patterning in vertebrate evolution and suggest that Hoxa2 function is required at late stages of BA2 development.     

Cytosolic nucleic acid sensors and innate immune regulation

During viral and bacterial infections, pathogen-derived cytosolic nucleic acids are recognized by the intracellular RNA sensors retinoic acid-inducible gene I and melanoma-differentiated gene 5 and intracellular DNA sensors, including cyclic-di-GMP-AMP synthase, absent in melanoma 2, interferon (IFN)–gamma inducible protein 16, polymerase III, and so on. Binding of intracellular nucleic acids to these sensors activates downstream signaling cascades, resulting in the production of type I IFNs and pro-inflammatory cytokines to induce appropriate systematic immune responses. While these sensors also recognize endogenous nucleic acids and activate immune responses, they can discriminate between self- and non-self-nucleic acids. However, dysfunction of these sensors or failure of regulatory mechanisms causes aberrant activation of immune response and autoimmune disorders. In this review, we focus on how intracellular immune sensors recognize exogenous nucleic acids and activate the innate immune system, and furthermore, how autoimmune diseases result from dysfunction of these sensors.     

Histone Deacetylases 1 and 2 Regulate Microglia Function during Development,Homeostasis, and Neurodegeneration in a Context-Dependent Manner

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Discovery of novel non-synonymous SNP variants in 988 candidate genes from 6 centenarians by target capture and next-generation sequencing

Despite evidence of a substantial genetic component, the genetic factors that underlie longevity in humans remain to be identified. Previous genome-wide linkage and association studies have not found strong evidence for the contribution of common variants besides the APOE gene, suggesting the role of rare variants in human longevity. To discover rare variants that might contribute to longevity, we selected 988 candidate genes and performed a pilot study to identify novel non-synonymous variants in 6 Ashkenazi Jewish centenarians older than 105. Our candidate genes act in pathways implicated in aging and longevity, including neurodegeneration, cognitive function, lipid metabolism, DNA repair, and genome maintenance. By implementing custom-designed Agilent SureSelect target capture and next-generation sequencing, we discovered a total of 89 novel non-synonymous SNPs (nsSNPs) and validated 51 nsSNPs by iPLEX MassArray assays. Genotyping analysis of these novel SNPs in 410 Ashkenazi Jewish controls and 390 centenarians showed significant enrichment (5.3 fold, p = 0.02) of the p.Y318C variant in PMS2 and significant depletion (7.5 fold, p = 0.04) of the p.V465A variant in GABRR3 in centenarians compared to controls. Our study presents the potential of targeted next-generation sequencing for discovery of rare but functional genetic variation which may lead to exceptional longevity in humans.     

RyR1 Deficiency in Congenital Myopathies Disrupts Excitation–Contraction Coupling

In skeletal muscle, excitation–contraction (EC) coupling is the process whereby the voltage‐gated dihydropyridine receptor (DHPR) located on the transverse tubules activates calcium release from the sarcoplasmic reticulum by activating ryanodine receptor (RyR1) Ca²⁺ channels located on the terminal cisternae. This subcellular membrane specialization is necessary for proper intracellular signaling and any alterations in its architecture may lead to neuromuscular disorders. In this study, we present evidence that patients with recessive RYR1‐related congenital myopathies due to primary RyR1 deficiency also exhibit downregulation of the alfa 1 subunit of the DHPR and show disruption of the spatial organization of the EC coupling machinery. We created a cellular RyR1 knockdown model using immortalized human myoblasts transfected with RyR1 siRNA and confirm that knocking down RyR1 concomitantly downregulates not only the DHPR but also the expression of other proteins involved in EC coupling. Unexpectedly, this was paralleled by the upregulation of inositol‐1,4,5‐triphosphate receptors; functionally however, upregulation of the latter Ca²⁺ channels did not compensate for the lack of RyR1‐mediated Ca²⁺ release. These results indicate that in some patients, RyR1 deficiency concomitantly alters the expression pattern of several proteins involved in calcium homeostasis and that this may influence the manifestation of these diseases.     

General Anesthesia Causes Long-Lasting Disturbances in the Ultrastructural Properties of Developing Synapses in Young Rats

Common general anesthetics administered to young rats at the peak of brain development cause widespread apoptotic neurodegeneration in their immature brain. Behavioral studies have shown that this leads to learning and memory deficiencies later in life. The subiculum, a part of the hippocampus proper and Papez’s circuit, is involved in cognitive development and is vulnerable to anesthesia-induced developmental neurodegeneration. This degeneration is manifested by acute substantial neuroapoptotic damage and permanent neuronal loss in later stages of synaptogenesis. Since synapse formation is a critical component of brain development, we examined the effects of highly neurotoxic anesthesia combination (isoflurane, nitrous oxide, and midazolam) on ultrastructural development of synapses in the rat subiculum. We found that this anesthesia, when administered at the peak of synaptogenesis, causes long-lasting injury to the subicular neuropil. This is manifested as neuropil scarcity and disarray, morphological changes indicative of mitochondria degeneration, a decrease in the number of neuronal profiles with multiple synaptic boutons and significant decreases in synapse volumetric densities. We believe that observed morphological disturbances of developing synapses may, at least in part, contribute to the learning and memory deficits that occur later in life after exposure of the immature brain to general anesthesia.