IASI-Derived Sea Surface Temperature Data Set for Climate Studies

Sea surface temperature (SST) is an essential climate variable, that is directly used in climate monitoring. Although satellite measurements can offer continuous global coverage, obtaining a long-term homogeneous satellite-derived SST data set suitable for climate studies based on a single instrument is still a challenge. In this work, we assess a homogeneous SST data set derived from reprocessed Infrared Atmospheric Sounding Interferometer (IASI) level-1 (L1C) radiance data. The SST is computed using Planck's Law and simple atmospheric corrections. We assess the data set using the ERA5 reanalysis and the EUMETSAT-released IASI level-2 SST product. Over the entire period, the reprocessed IASI SST shows a mean global difference with ERA5 close to zero, a mean absolute bias under 0.5°C, with a SD of difference around 0.3°C and a correlation coefficient over 0.99. In addition, the reprocessed data set shows a stable bias and SD, which is an advantage for climate studies. The interannual variability and trends were compared with other SST data sets: ERA5, Hadley Centre's SST (HadISST), and NOAA's Optimal Interpolation SST Analysis (OISSTv2). We found that the reprocessed SST data set is able to capture the patterns of interannual variability well, showing the same areas of high interannual variability (>1.5°C), including over the tropical Pacific in January corresponding to the El Niño Southern Oscillation. Although the period studied is relatively short, we demonstrate that the IASI data set reproduces the same trend patterns found in the other data sets (i.e., cooling trend in the North Atlantic, warming trend over the Mediterranean).

[Disseminated erythematous lupus with bilateral diaphragmatic involvement]

The diaphragm is an unusual localization for disseminated erythematous lupus and is generally not recognized. We present the case of a 34-year-old woman who developed bilateral pain in the base of the thorax 15 days before hospitalization without any bronchial signs and NYHA stage II dyspnea. The patient's general health status remained satisfactory and the physical examination was normal except for diffuse inflammatory joint pain and cutaneous photosensitivization. The chest x-ray disclosed ascension of both hemidiaphragms with retracted lungs associated with bilateral basal atalectasia. The diagnosis of lupus with diaphragmatic involvement was retained due to the clinical presentation with diffuse joint pain, photosensitization with facial erythema, pericardial effusion and elevated antinuclear antibody and lymphopenia (1 100/mm3). Lung function tests revealed a restrictive syndrome. Oral corticosteroids 1 mg/kg/d enabled clinical and functional improvement. In light of this observation we discuss the pathogenic mechanisms of this uncommon localization of lupus and the difficulty of establishing a sure diagnosis.

Ocsyn, a novel syntaxin-interacting protein enriched in the subapical region of inner hair cells

Sensory (hair) cells of the inner ear contain two specialized areas of membrane delivery. The first, located at the cell base, is the afferent synapse where rapid delivery of synaptic vesicles is required to convey information about auditory signals with exceedingly high temporal precision. The second area is at the apex. To accommodate the continuous movement of stereocilia and facilitate their repair, recycling of membrane components is required. Intense vesicular traffic is restricted to a narrow band of cytoplasm around the cuticular plate, which anchors stereocilia. Our previous analyses showed that SNARE proteins (syntaxin 1A/SNAP25/VAMP1) are concentrated at both poles of hair cells, consistent with their involvement in membrane delivery at both locations. To investigate further the molecules involved in membrane delivery at these two sites, we constructed a two-hybrid library of the organ of Corti and probed it with syntaxin 1A. Here we report the cloning of a novel syntaxin-binding protein that is concentrated in a previously uncharacterized organelle at the apex of inner hair cells.

Vezatin, a novel transmembrane protein, bridges myosin VIIA to the cadherin-catenins complex

Defects in myosin VIIA are responsible for deafness in the human and mouse. The role of this unconventional myosin in the sensory hair cells of the inner ear is not yet understood. Here we show that the C-terminal FERM domain of myosin VIIA binds to a novel transmembrane protein, vezatin, which we identified by a yeast two-hybrid screen. Vezatin is a ubiquitous protein of adherens cell-cell junctions, where it interacts with both myosin VIIA and the cadherin-catenins complex. Its recruitment to adherens junctions implicates the C-terminal region of alpha-catenin. Taken together, these data suggest that myosin VIIA, anchored by vezatin to the cadherin-catenins complex, creates a tension force between adherens junctions and the actin cytoskeleton that is expected to strengthen cell-cell adhesion. In the inner ear sensory hair cells vezatin is, in addition, concentrated at another membrane-membrane interaction site, namely at the fibrillar links interconnecting the bases of adjacent stereocilia. In myosin VIIA-defective mutants, inactivity of the vezatin-myosin VIIA complex at both sites could account for splaying out of the hair cell stereocilia.

Unconventional myosin VIIA is a novel A-kinase-anchoring protein

To gain an insight into the cellular function of the unconventional myosin VIIA, we sought proteins interacting with its tail region, using the yeast two-hybrid system. Here we report on one of the five candidate interactors we identified, namely the type I alpha regulatory subunit (RI alpha) of protein kinase A. The interaction of RI alpha with myosin VIIA tail was demonstrated by coimmunoprecipitation from transfected HEK293 cells. Analysis of deleted constructs in the yeast two-hybrid system showed that the interaction of myosin VIIA with RI alpha involves the dimerization domain of RI alpha. In vitro binding assays identified the C-terminal "4.1, ezrin, radixin, moesin" (FERM)-like domain of myosin VIIA as the interacting domain. In humans and mice, mutations in the myosin VIIA gene underlie hereditary hearing loss, which may or may not be associated with visual deficiency. Immunohistofluorescence revealed that myosin VIIA and RI alpha are coexpressed in the outer hair cells of the cochlea and rod photoreceptor cells of the retina. Our results strongly suggest that myosin VIIA is a novel protein kinase A-anchoring protein that targets protein kinase A to definite subcellular sites of these sensory cells.

KCNQ4, a K+ channel mutated in a form of dominant deafness, is expressed in the inner ear and the central auditory pathway

Mutations in the potassium channel gene KCNQ4 underlie DFNA2, an autosomal dominant form of progressive hearing loss in humans. In the mouse cochlea, the transcript has been found exclusively in the outer hair cells. By using specific antibodies, we now show that KCNQ4 is situated at the basal membrane of these sensory cells. In the vestibular organs, KCNQ4 is restricted to the type I hair cells and the afferent calyx-like nerve endings ensheathing these sensory cells. Several lines of evidence suggest that KCNQ4 underlies the I(K,n) and g(K,L) currents that have been described in the outer and type I hair cells, respectively, and that are already open at resting potentials. KCNQ4 is also expressed in neurons of many, but not all, nuclei of the central auditory pathway, and is absent from most other brain regions. It is present, e.g., in the cochlear nuclei, the nuclei of the lateral lemniscus, and the inferior colliculus. This is the first ion channel shown to be specifically expressed in a sensory pathway. Moreover, the expression pattern of KCNQ4 in the mouse auditory system raises the possibility of a central component in the DFNA2 hearing loss.

SNARE complex at the ribbon synapses of cochlear hair cells: analysis of synaptic vesicle- and synaptic membrane-associated proteins

Neurotransmitters are released via exocytosis of synaptic vesicles involving a fusion complex consisting of a set of highly conserved proteins, which form a multiprotein complex resulting in the docking of synaptic vesicles at the site of release. There are three major differences between cochlear hair cell synapses and CNS synapses: (i) hair cells have a specialized structure, the synaptic ribbon, to which synaptic vesicles are attached; (ii) hair cells can maintain high and sustained release of neurotransmitter; and (iii) hair cells lack synaptophysin and synapsin. These differences suggest that an unconventional mechanism of neurotransmitter release may be involved at ribbon synapses. In this study we used different and complementary approaches to determine whether or not ribbon-containing hair cells of the cochlea express any component of the core fusion complex found in conventional synapses. Syntaxin 1, the synaptic membrane synaptosome-associated protein (SNAP)-25 and vesicle-associated membrane protein (VAMP or synaptobrevin) were found to be present in the organ of Corti of both rat and guinea-pig, as shown by reverse transcription polymerase chain reaction and Western blotting. In situ hybridization and immunocytochemistry showed mRNA and protein expression, respectively, in both inner and outer hair cells. Synaptotagmins I and II, generally considered to play major roles in neurotransmitter release at central synapses, were not detected in the organ of Corti.

The glutamate receptor subunit delta1 is highly expressed in hair cells of the auditory and vestibular systems

In the inner ear, fast excitatory synaptic transmission is mediated by ionotropic glutamate receptors, including AMPA, kainate, and NMDA receptors. The recently identified delta1 and delta2 glutamate receptors share low homology with the other three types, and no clear response or ligand binding has been obtained from cells transfected with delta alone or in combination with other ionotropic receptors. Studies of mice lacking expression of delta2 show that this subunit plays a crucial role in plasticity of cerebellar glutamatergic synapses. In addition, these mice show a deficit in vestibular compensation. These findings and the nature of glutamatergic synapses between vestibulocochlear hair cells and primary afferent dendrites suggest that delta receptors may be functionally important in the inner ear and prompted us to investigate the expression of delta receptors in the cochlea and peripheral vestibular system. Reverse transcription and DNA amplification by PCR combined with immunocytochemistry and in situ hybridization were used. Our results show that the expression of delta1 in the organ of Corti is intense and restricted to the inner hair cells, whereas delta1 is expressed in all spiral ganglion neurons as well as in their satellite glial cells. In the vestibular end organ, delta1 was highly expressed in both hair cell types and also was expressed in the vestibular ganglion neurons. The prominent expression of delta1 in inner hair cells and in type I and type II vestibular hair cells suggests a functional role in hair cell neurotransmission.

Choline acetyltransferase, glutamate decarboxylase, tyrosine hydroxylase, calcitonin gene-related peptide and opioid peptides coexist in lateral efferent neurons of rat and guinea-pig

The lateral efferent (olivocochlear) innervation of the cochlea originates in the brainstem lateral superior olive. It is likely to use acetylcholine, gamma-aminobutyric acid, dopamine and various neuropeptides as neurotransmitters and/or neuromodulators. In order to determine the different coexistence patterns of these molecules in lateral efferent perikarya, we have used double and triple immunofluorescence co-localization techniques to colocalize choline acetyltransferase, glutamate decarboxylase, tyrosine hydroxylase, calcitonin gene-related peptide and enkephalins in single sections of the lateral superior olive. We also used a non-radioactive in situ hybridization technique onto serial sections of this nucleus to confirm the immunofluorescence co-localization data at the mRNA level. Whatever the pair or triplet of primary antibodies tested was, a high ratio of coexistence was observed in the immunofluorescence experiments. In triple co-localization experiments, 90-93% of the choline acetyltransferase-like immunoreactive neurons were also immunoreactive to the two other antigens investigated. The in situ hybridization co-localization data, based on the use of biotin-labelled oligoprobes, qualitatively confirmed these immunofluorescence data. In conclusion, it can be postulated that acetylcholine, gamma-aminobutyric acid, dopamine, calcitonin gene-related peptide, enkephalins and dynorphins (whose coexistence with choline acetyltransferase and enkephalins has been previously described immunocytochemically) coexist in lateral efferent neurons. Based on these results, it is tempting to propose the lateral efferent innervation as a useful model with which the functional implications of the coexistence of neurotransmitters/neuromodulators can be investigated in vivo.

Molecular analysis of excitatory amino acid receptor expression in the cochlea

Our present understanding of excitatory neurotransmission has expanded enormously in the last decade through the use of molecular biology. In the mammalian cochlea, the analysis of excitatory amino acid receptor expression by the reverse transcription-polymease chain reaction (RT-PCR), in situ hybridization and immunochemistry has provided considerable evidence for glutamate as the afferent neurotransmitter. Using these molecular techniques, the ionotropic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), kainate, N-methyl-D-aspartic acid (NMDA) and delta receptor subunits and the metabotropic glutamate receptors have all been detected in the cochlea, in either the spiral ganglion neurons, the hair cells or both. Due to the utility of the techniques and the diversity of expressed neurotransmitter receptors, molecular biology will continue to provide important information for researchers of the auditory periphery.

Pre- and postsynaptic M3 muscarinic receptor mRNAs in the rodent peripheral auditory system

The medial and lateral efferent innervations originate from distinct parts of the superior olivary complex. Both use acetylcholine, respectively, to modulate the activity of outer hair cells (OHC), and spiral ganglion neurons (SGN) which are postsynaptic to the inner hair cells (IHC). Besides predominantly activating nicotinic receptors, acetylcholine recognizes muscarinic M3 receptors, whose the role(s) and cellular localization(s) are not yet firmly established. We used reverse transcription and polymerase chain reaction to amplify the M3 receptor cDNA in the rat and guinea pig organ of Corti and spiral ganglion. Then, we localized the M3 receptor mRNAs in cochleas and superior olivary complex of both species. The M3 receptor cDNA was amplified from samples of brain, organ of Corti and spiral ganglion. Indeed, its corresponding mRNA was localized in SGNs, OHCs and IHCs. However, in the apical turns, OHCs were often found unlabeled. In the superior olivary complex, M3 mRNAs were colocalized with choline acetyltransferase mRNAs in neurons of the lateral superior olive and ventral nucleus of the trapezoid body. These results suggest that the M3 receptor-induced inositol phosphate formation described in previous studies [21] takes place in both postsynaptic (SGNs, OHCs) and presynaptic components of efferent cochlear synapses, and in cells that are not contacted by efferents in the adult cochlea (IHCs).

Expression of mGluR1 alpha mRNA receptor in rat and guinea pig cochlear neurons

Glutamate or a parent substance is thought to be the afferent neurotransmitter in the auditory system. In situ hybridization showed that mGluR1 alpha mRNA was expressed by type I and type II spiral ganglion neurons in the cochlea. The glial cells surrounding the type I spiral ganglion neurons lacked such expression. The hybridization signal was low compared to that reported for non-NMDA receptors, suggesting that mGluR1 alpha receptors, as is the case for NMDA receptors, play a minor role in auditory transmission. The uniform expression of mGluR1 alpha mRNAs along the cochlear spiral suggests their co-expression in spiral ganglion neurons with NMDA and non-NMDA receptors and thus functional cooperation.

Co-expression of NMDA and AMPA/kainate receptor mRNAs in cochlear neurones

The co-expression of NMDAR-1 and GluR1-4 mRNAs in spiral ganglions of rat and guinea-pig cochleas was checked using a non-radioactive in situ hybridization technique. NMDAR-1, GluR2 and GluR3 mRNAs were expressed in the large neurones (type I) of the ganglion which innervate inner hair cells (IHCs), a sensory cell type likely to use an excitatory amino acid as a neurotransmitter. The labelling was very intense with the GluR2 and GluR3 oligoprobes while it remained moderate with the NMDAR-1 oligoprobe. This is consistent with the predominant implication of AMPA/kainate receptors in the physiological and early pathophysiological aspects of the IHC neurotransmission. Spiral ganglion neurones did not express GluR1 and GluR4 mRNAs, but a glial expression of GluR4 mRNAs was observed.