FGF signaling regulates development by processes beyond canonical pathways.

FGFs are key developmental regulators that engage a signal transduction cascade through receptor tyrosine kinases, prominently engaging ERK1/2 but also other pathways. However, it remains unknown whether all FGF activities depend on this canonical signal transduction cascade. To address this question, we generated allelic series of knock-in Fgfr1 and Fgfr2 mouse strains, carrying point mutations that disrupt binding of signaling effectors, and a kinase dead allele of Fgfr2 that broadly phenocopies the null mutant. When interrogated in cranial neural crest cells, we identified discrete functions for signaling pathways in specific craniofacial contexts, but point mutations, even when combined, failed to recapitulate the single or double null mutant phenotypes. Furthermore, the signaling mutations abrogated established FGF-induced signal transduction pathways, yet FGF functions such as cell-matrix and cell-cell adhesion remained unaffected, though these activities did require FGFR kinase activity. Our studies establish combinatorial roles of Fgfr1 and Fgfr2 in development and uncouple novel FGFR kinase-dependent cell adhesion properties from canonical intracellular signaling.

FGF signaling regulates salivary gland branching morphogenesis by modulating cell adhesion.

Loss of FGF signaling leads to defects in salivary gland branching, but the mechanisms underlying this phenotype remain largely unknown. We disrupted expression of Fgfr1 and Fgfr2 in salivary gland epithelial cells and found that both receptors function coordinately in regulating branching. Strikingly, branching morphogenesis in double knockouts is restored by Fgfr1 and Fgfr2 (Fgfr1/2) knock-in alleles incapable of engaging canonical RTK signaling, suggesting that additional FGF-dependent mechanisms play a role in salivary gland branching. Fgfr1/2 conditional null mutants showed defective cell-cell and cell-matrix adhesion, both of which have been shown to play instructive roles in salivary gland branching. Loss of FGF signaling led to disordered cell-basement membrane interactions in vivo as well as in organ culture. This was partially restored upon introducing Fgfr1/2 wild-type or signaling alleles that are incapable of eliciting canonical intracellular signaling. Together, our results identify non-canonical FGF signaling mechanisms that regulate branching morphogenesis through cell-adhesion processes.

Experimental study on transit time broadening in rubidium 5S-5D excitation.

In this experimental work, we report our findings about a transition between states of even parity 5S1/2→5D5/2 of Rb atoms under different conditions of transit time broadening. For this purpose, the blue fluorescence emanating from the associated decay 5D5/2→6P3/2→5S1/2 channel is monitored. Based on the relative magnification of the laser beam, which is used in excitation between levels of even parity, the system exhibits two photon absorption (TPA) through blue fluorescence peaks. The TPA profile appears as a Lorentzian peak on a Doppler background. The change in the laser beam diameter directly influences the relative contributions of Lorentzian and Doppler parts. A direct inference drawn from of this study may be utilized in optimizing the extraction of the first derivative spectrum corresponding to 5S→5D transitions.

Precise spatial restriction of BMP signaling in developing joints is perturbed upon loss of embryo movement.

Dynamic mechanical loading of synovial joints is necessary for normal joint development, as evidenced in certain clinical conditions, congenital disorders and animal models where dynamic muscle contractions are reduced or absent. Although the importance of mechanical forces on joint development is unequivocal, little is known about the molecular mechanisms involved. Here, using chick and mouse embryos, we observed that molecular changes in expression of multiple genes analyzed in the absence of mechanical stimulation are consistent across species. Our results suggest that abnormal joint development in immobilized embryos involves inappropriate regulation of Wnt and BMP signaling during definition of the emerging joint territories, i.e. reduced ß-catenin activation and concomitant upregulation of pSMAD1/5/8 signaling. Moreover, dynamic mechanical loading of the developing knee joint activates Smurf1 expression; our data suggest that Smurf1 insulates the joint region from pSMAD1/5/8 signaling and is essential for maintenance of joint progenitor cell fate.

Exploring hyperfine levels of non-Rydberg excited states in a Ξ system using Autler-Townes splitting.

In this experimental work we report our findings about a cascade (Ξ) transition 5S1/2→5P3/2→5D3/2 of both 85,87Rb atoms under different laser detuning combinations. The relative power levels of two individual lasers are adjusted under a counter-propagating configuration so that the system exhibits Autler-Townes splitting (ATS). However, the ATS, which is otherwise difficult to detect in a room-temperature alkali vapor cell offering large Doppler background, is well resolved here by using a combination of modulation transfer and phase-sensitive detection techniques. The results show that the AT components clearly indicate the hyperfine structure of 5D3/2 level for 87Rb isotope. For 85Rb, the resolution of ATS is limited by the relatively closer proximity of 5D3/2 hyperfine components. The results are also verified through blue fluorescence detection by monitoring the 5D3/2→6P3/2→5S1/2 non-degenerate decay arm. The technique is easy to implement and is able to reveal the hyperfine structure of the excited levels. However, the technique is not a good choice when an excited level with dense hyperfine structure is targeted.

Precise spatial restriction of BMP signaling is essential for articular cartilage differentiation.

The articular cartilage, which lines the joints of the limb skeleton, is distinct from the adjoining transient cartilage, and yet, it differentiates as a unique population within a contiguous cartilage element. Current literature suggests that articular cartilage and transient cartilage originate from different cell populations. Using a combination of lineage tracing and pulse-chase of actively proliferating chondrocytes, we here demonstrate that, similar to transient cartilage, embryonic articular cartilage cells also originate from the proliferating chondrocytes situated near the distal ends of skeletal anlagen. We show that nascent cartilage cells are capable of differentiating as articular or transient cartilage, depending on exposure to Wnt or BMP signaling, respectively. The spatial organization of the articular cartilage results from a band of Nog-expressing cells, which insulates these proliferating chondrocytes from BMP signaling and allows them to differentiate as articular cartilage under the influence of Wnt signaling emanating from the interzone. Through experiments conducted in both chick and mouse embryos we have developed a model explaining simultaneous growth and differentiation of transient and articular cartilage in juxtaposed domains.

Blue fluorescence as a frequency offset reference in the rubidium 5S-5P-5D transition.

In this work, we address the issue of the suitability of blue fluorescent light as a frequency offset reference during the ladder-level excitation 5S1/2→5P3/2→5D3/2 of Rb85 atoms. A simple pump-probe spectroscopy experiment is performed to generate non-degenerate blue light emission produced by the spontaneous decay route 5D3/2→6P3/2→5S1/2. By varying the relative intensity of the pump-probe combination, we can hover between regimes dominated by mechanisms such as double resonance optical pumping (DROP) and Autler-Townes splitting. The efficacy of the blue fluorescence (420 nm) as a frequency offset reference is pronounced under the DROP regime due to its narrow (∼natural) linewidth. To provide further insight into the stability performance, the pump laser connecting the 5P3/2→5D3/2 transition is stabilized to the peak of the blue light with the help of a probe stabilized to the saturation absorption signal of the 5S1/2→5P3/2 transition. For this purpose, we used the coherence-induced modulation transfer technique. The error frequency noise power spectra and the subsequent Allan variance calculation clearly show that probe fluctuations are transferred to the pump laser because of an existing two-photon coherent coupling.

Non-contact control of two-photon absorption.

In this experimental work, we address the issue of the control of two-photon absorption in a Doppler broadened medium of Rb85 atoms under the ladder level coupling 5S1/2→5P3/2→5D3/2. Here, suppression and enhancement of two-photon absorption are executed by applying an auxiliary laser beam, which is not physically propagating in the same line of the pump-probe combination. Instead, the auxiliary beam, which is in resonance with the Rb85 D2 transition, is at a finite distance from the line of propagation of the pump-probe combination. The resonant auxiliary beam produces an atomic beam in the vapor cell, and when it reaches the pump-probe path, it creates an asymmetry in the population of ground state hyperfine components. This asymmetry is responsible for controlling two-photon absorption. We present here results obtained by us along with a qualitative explanation of the physical principles behind the control mechanism.

Effect of continuous vs sequential chelation on the mechanical properties of root dentin: An ex vivo study.

OBJECTIVES: To evaluate the mechanical properties of root canal dentin treated with sodium hypochlorite (NaOCl) in combination with hydroxyethylidene diphosphonic acid (HEDP) or ethylenediaminetetraacetic acid (EDTA). METHODS: For testing fracture resistance, 45 single-rooted teeth were instrumented and irrigated with NaOCl/HEDP, NaOCl/EDTA, or distilled water. Fifteen untreated teeth served as control. After obturation, specimens from the experimental groups were thermocycled, dynamically-loaded, and then statically-loaded in a universal testing machine until failure. For flexural strength analysis, 15 teeth were instrumented and irrigated with NaOCl/HEDP or NaOCl/EDTA. Root segments were sectioned into dentin bars and tested for flexural strength using a universal testing machine. For microhardness evaluation, 20 teeth were instrumented and irrigated with NaOCl/HEDP or NaOCl/EDTA. Dentin disks from the coronal-third of each root segment were prepared, one before and one after irrigation, for microhardness testing with a Knoop hardness tester. RESULTS: The highest fracture resistance was recorded in the untreated group, and the lowest in the EDTA group. Although the HEDP group had higher fracture resistance than the EDTA group, the distilled water group demonstrated even greater fracture resistance than the HEDP group. Specimens treated with HEDP had significantly higher flexural strength and microhardness values when compared with those treated with EDTA. CONCLUSION: The fracture resistance, flexural strength, and microhardness of root canal dentin were higher when root canals were irrigated with NaOCl/HEDP, when compared with NaOCl/EDTA. CLINICAL SIGNIFICANCE: Irrigating root canals with NaOCl combined with HEDP significantly improves the mechanical integrity of root canal dentin compared to the use of NaOCl with EDTA.

Development of a gas jet coupled electron cyclotron resonance ion source for radioactive ion beam.

A 2.45 GHz electron cyclotron resonance (ECR) ion source coupled to a gas-jet skimmer system has been developed for the online production of radioactive ion beams (RIBs). Using radial injection of gas jet in the ion source, RIBs of 11C1+, 11CO21+, and 11CO1+ have been produced online with beam intensity up to about 9 × 103 particles per second for a 1 µA primary proton beam bombarding a nitrogen gas target. The details of the gas jet coupled ECR ion source and the results for stable isotope beams and RIBs are reported.

A comprehensive mRNA expression analysis of developing chicken articular cartilage.

Articular cartilage present at the ends of appendicular skeletal elements provides friction-less movement to the synovial joints and any damage to this tissue can lead to a degenerative disease of joint called osteoarthritis. During past two decades although many genes e.g.,Gdf5, Wnt9a, Noggin etc. have been identified and characterized in joint development, still a comprehensive understanding of molecular network(s) operational in articular cartilage morphogenesis is far from being drawn. Here we report identification of 36 genes (19 from literature survey and 17 from microarray analysis) that are expressed in developing chicken phalangeal joints in a spatiotemporally dynamic manner. For both these set of genes across the time window investigated we observed three kinds of expression patterns: early, late and constant. The early expressed genes are invariably expressed in a domain broader than the interzone while the late expressed genes are expressed in restricted spatial domains. The comprehensive expression analysis presented in this report provides a candidate list of molecular players involved in articular cartilage differentiation and/or maintenance.

Elastic properties of nanoparticle monolayer foams.

Monolayers of nanosized carboxylate-functionalized polystyrene particles at the air/water interface assemble into two coexisting liquid phases of different densities. The rheological properties of the individual phases and of the resulting nanoparticle texture is measured using a magnetic needle microrheometer. We show that, despite the liquid behavior of the individual viscous phases, the entire structure exhibits elastic response to local deformations induced by the needle. We explain this response by microscopically nonresolved nanofacets that connect the domains and form a two-dimensional foam.