Pressure sensitivity of SynGAP/PSD-95 condensates as a model for postsynaptic densities and its biophysical and neurological ramifications

Biomolecular condensates consisting of proteins and nucleic acids can serve critical biological functions, so that some condensates are referred as membraneless organelles. They can also be disease-causing, if their assembly is misregulated. A major physicochemical basis of the formation of biomolecular condensates is liquid–liquid phase separation (LLPS). In general, LLPS depends on environmental variables, such as temperature and hydrostatic pressure. The effects of pressure on the LLPS of a binary SynGAP/PSD-95 protein system mimicking postsynaptic densities, which are protein assemblies underneath the plasma membrane of excitatory synapses, were investigated. Quite unexpectedly, the model system LLPS is much more sensitive to pressure than the folded states of typical globular proteins. Phase-separated droplets of SynGAP/PSD-95 were found to dissolve into a homogeneous solution already at ten-to-hundred bar levels. The pressure sensitivity of SynGAP/PSD-95 is seen here as a consequence of both pressure-dependent multivalent interaction strength and void volume effects. Considering that organisms in the deep sea are under pressures up to about 1 kbar, this implies that deep-sea organisms have to devise means to counteract this high pressure sensitivity of biomolecular condensates to avoid harm. Intriguingly, these findings may shed light on the biophysical underpinning of pressure-related neurological disorders in terrestrial vertebrates

Developmental expression of BK channels in chick cochlear hair cells

<p>Abstract</p> <p>Background</p> <p>Cochlear hair cells are high-frequency sensory receptors. At the onset of hearing, hair cells acquire fast, calcium-activated potassium (BK) currents, turning immature spiking cells into functional receptors. In non-mammalian vertebrates, the number and kinetics of BK channels are varied systematically along the frequency-axis of the cochlea giving rise to an intrinsic electrical tuning mechanism. The processes that control the appearance and heterogeneity of hair cell BK currents remain unclear.</p> <p>Results</p> <p>Quantitative PCR results showed a non-monotonic increase in BK α subunit expression throughout embryonic development of the chick auditory organ (i.e. basilar papilla). Expression peaked near embryonic day (E) 19 with six times the transcript level of E11 sensory epithelia. The steady increase in gene expression from E11 to E19 could not explain the sudden acquisition of currents at E18-19, implicating post-transcriptional mechanisms. Protein expression also preceded function but progressed in a sequence from diffuse cytoplasmic staining at early ages to punctate membrane-bound clusters at E18. Electrophysiology data confirmed a continued refinement of BK trafficking from E18 to E20, indicating a translocation of BK clusters from supranuclear to subnuclear domains over this critical developmental age.</p> <p>Conclusions</p> <p>Gene products encoding BK α subunits are detected up to 8 days before the acquisition of anti-BK clusters and functional BK currents. Therefore, post-transcriptional mechanisms seem to play a key role in the delayed emergence of calcium-sensitive currents. We suggest that regulation of translation and trafficking of functional α subunits, near voltage-gated calcium channels, leads to functional BK currents at the onset of hearing.</p

Molecular Detection of Candidatus Coxiella mudorwiae in Haemaphysalis concinna in China

Coxiella burnetii and Coxiella -like endosymbionts (CLEs) have been widely discovered in various ticks, animals, and even human beings. To estimate the possible origin of C. burnetii and its relatives CLEs, the prevalence of C. burnetii and CLEs has been intensively surveyed all over the world. In the present study, the possible infection of C. burnetii and CLEs in host-seeking Haemaphysalis concinna was performed with meta-transcript analysis with tick specimens harvested from Mudanjiang City, Heilongjiang province, China. The meta-transcript results were subsequently confirmed by the specific sequence of partial 16S rRNA. A total of three arrays of gene transcripts were harvested, including pyrophosphate-fructose 6-phosphate 1-phosphotransferase- eda -thiol-disulfide isomerase and thioredoxin- greA , carB - carA-DnaJ-DnaK-grpE-ppnk , ropC-ropB , and ubiA- non-canonical purine NTP pyrophosphatase- hemK-prfA , which suggest the infection of Candidatus Coxiella mudorwiae in H. concinna . The high identity of the 16S rRNA gene of Candidatus C. mudorwiae achieved in our study strongly supports our meta-transcripts analysis. The prevalence of Candidatus C. mudorwiae in hard ticks has been discovered in China. More detailed surveys are imperative to clarify the emergence of CLEs and their implication in the epidemiologic characteristics of Q fever