Phosphorylation of Shox2 Is Required for Its Function to Control Sinoatrial Node Formation

Background: Inactivation of Shox2, a member of the short‐stature homeobox gene family, leads to defective development of multiple organs and embryonic lethality as a result of cardiovascular defects, including bradycardia and severe hypoplastic sinoatrial node (SAN) and sinus valves, in mice. It has been demonstrated that Shox2 regulates a genetic network through the repression of Nkx2.5 to maintain the fate of the SAN cells. However, the functional mechanism of Shox2 protein as a transcriptional repressor on Nkx2.5 expression remains completely unknown. Methods and Results: A specific interaction between the B56δ regulatory subunit of PP2A and Shox2a, the isoform that is expressed in the developing heart, was demonstrated by yeast 2‐hybrid screen and coimmunoprecipitation. Western blotting and immunohistochemical assays further confirmed the presence of phosphorylated Shox2a (p‐Shox2a) in cell culture as well as in the developing mouse and human SAN. Site‐directed mutagenesis and in vitro kinase assays identified Ser92 and Ser110 as true phosphorylation sites and substrates of extracellular signal‐regulated kinase 1 and 2. Despite that Shox2a and its phosphorylation mutants possessed similar transcriptional repressive activities in cell cultures when fused with Gal4 protein, the mutant forms exhibited a compromised repressive effect on the activity of the mouse Nkx2.5 promoter in cell cultures, indicating that phosphorylation is required for Shox2a to repress Nkx2.5 expression specifically. Transgenic expression of Shox2a, but not Shox2a‐S92AS110A, mutant in the developing heart resulted in down‐regulation of Nkx2.5 in wild‐type mice and rescued the SAN defects in the Shox2 mutant background. Last, we demonstrated that elimination of both phosphorylation sites on Shox2a did not alter its nuclear location and dimerization, but depleted its capability to bind to the consensus sequences within the Nkx2.5 promoter region. Conclusions: Our studies reveal that phosphorylation is essential for Shox2a to repress Nkx2.5 expression during SAN development and differentiation

Meta-analysis of relationship between short-term ozone exposure and population mortality in China

BackgroundIn recent years, our country's atmospheric particulate matter pollution has improved significantly, while ozone (O3) pollution has become increasingly serious. As a secondary pollutant, O3 is closely related to human health. ObjectiveTo study the effect of short-term exposure to ozone in ambient air on population mortality in China. MethodsA computer search with key words of "ozone or O3", "death", and "time series" in Chinese or "ozone", "mortality", and "China" in English was performed in Web of Science, PubMed, China National Knowledge Infrastructure, Wanfang, and VIP databases to find literature on effects of short-term ozone exposure on population mortality covering a time period from January 1, 1990 to December 31, 2021. According to a set of inclusion and exclusion criteria developed for this study, literaturescreening, quality evaluation, andrelevant data extraction were carried out. Finally, R 4.1.2 software was used to perform meta-analysis to estimate target effect sizes. ResultsA total of 978 articles were retrieved. According to the inclusion and exclusion criteria, 18 articles were finally included, including 39 effect size estimates. The results showed that every 10 μɡ·m−3 increase in ambient ozone concentration was associated with an increase of 0.45% (95%CI: 0.39%-0.51%), 0.50% (95%CI: 0.33%-0.68%), and 0.60% (95%CI: 0.48%-0.72%) in total, respiratory, and cardiovascular disease mortalities , respectively. The results of subgroup analysis by age, sex, and season showed that when ozone concentration increased 10 μɡ·m−3, an increase of 0.34% (95%CI: 0.17%-0.51%) in mortality was observed in the ≥ 65-year-old population, higher than 0.09% (95%CI: −0.21%-0.39%) increase in the <65-year-old population; the mortality increase in females [0.44% (95%CI: 0.30%-0.58%)] was greater than that in males [0.35% (95%CI: 0.22%-0.48%)]; compared with the warm season [0.29% (95%CI: 0.16%-0.42%)], mortality increase was higher in the cold season [1.03% (95%CI: 0.71%-1.35%)]. ConclusionAmbient ozone is an important factor affecting population mortality. The elderly and women ≥ 65 years old in China are more sensitive to ozone, and the impact of ozone exposure on population mortality is greater in cold season

Overexpression of Fgf18 in cranial neural crest cells recapitulates Pierre Robin sequence in mice

The pivotal role of FGF18 in the regulation of craniofacial and skeletal development has been well established. Previous studies have demonstrated that mice with deficiency in Fgf18 exhibit severe craniofacial dysplasia. Recent clinical reports have revealed that the duplication of chromosome 5q32-35.3, which encompasses the Fgf18 gene, can lead to cranial bone dysplasia and congenital craniosynostosis, implicating the consequence of possible overdosed FGF18 signaling. This study aimed to test the effects of augmented FGF18 signaling by specifically overexpressing the Fgf18 gene in cranial neural crest cells using the Wnt1-Cre;pMes-Fgf18 mouse model. The results showed that overexpression of Fgf18 leads to craniofacial abnormalities in mice similar to the Pierre Robin sequence in humans, including abnormal tongue morphology, micrognathia, and cleft palate. Further examination revealed that elevated levels of Fgf18 activated the Akt and Erk signaling pathways, leading to an increase in the proliferation level of tongue tendon cells and alterations in the contraction pattern of the genioglossus muscle. Additionally, we observed that excessive FGF18 signaling contributed to the reduction in the length of Meckel’s cartilage and disrupted the development of condylar cartilage, ultimately resulting in mandibular defects. These anomalies involve changes in several downstream signals, including Runx2, p21, Akt, Erk, p38, Wnt, and Ihh. This study highlights the crucial role of maintaining the balance of endogenous FGF18 signaling for proper craniofacial development and offers insights into potential formation mechanisms of the Pierre Robin sequence

A common Shox2–Nkx2-5 antagonistic mechanism primes the pacemaker cell fate in the pulmonary vein myocardium and sinoatrial node

In humans, atrial fibrillation is often triggered by ectopic pacemaking activity in the myocardium sleeves of the pulmonary vein (PV) and systemic venous return. The genetic programs that abnormally reinforce pacemaker properties at these sites and how this relates to normal sinoatrial node (SAN) development remain uncharacterized. It was noted previously that Nkx2-5, which is expressed in the PV myocardium and reinforces a chamber-like myocardial identity in the PV, is lacking in the SAN. Here we present evidence that in mice Shox2 antagonizes the transcriptional output of Nkx2-5 in the PV myocardium and in a functional Nkx2-5(+) domain within the SAN to determine cell fate. Shox2 deletion in the Nkx2-5(+) domain of the SAN caused sick sinus syndrome, associated with the loss of the pacemaker program. Explanted Shox2(+) cells from the embryonic PV myocardium exhibited pacemaker characteristics including node-like electrophysiological properties and the capability to pace surrounding Shox2(−) cells. Shox2 deletion led to Hcn4 ablation in the developing PV myocardium. Nkx2-5 hypomorphism rescued the requirement for Shox2 for the expression of genes essential for SAN development in Shox2 mutants. Similarly, the pacemaker-like phenotype induced in the PV myocardium in Nkx2-5 hypomorphs reverted back to a working myocardial phenotype when Shox2 was simultaneously deleted. A similar mechanism is also adopted in differentiated embryoid bodies. We found that Shox2 interacts with Nkx2-5 directly, and discovered a substantial genome-wide co-occupancy of Shox2, Nkx2-5 and Tbx5, further supporting a pivotal role for Shox2 in the core myogenic program orchestrating venous pole and pacemaker development

Recurrent chromosome reshuffling and the evolution of neo-sex chromosomes in parrots

The karyotype of most birds has remained considerably stable during more than 100 million years’ evolution, except for some groups, such as parrots. The evolutionary processes and underlying genetic mechanism of chromosomal rearrangements in parrots, however, are poorly understood. Here, using chromosome-level assemblies of four parrot genomes, we uncover frequent chromosome fusions and fissions, with most of them occurring independently among lineages. The increased activities of chromosomal rearrangements in parrots are likely associated with parrot-specific loss of two genes, ALC1 and PARP3, that have known functions in the repair of double-strand breaks and maintenance of genome stability. We further find that the fusion of the ZW sex chromosomes and chromosome 11 has created a pair of neo-sex chromosomes in the ancestor of parrots, and the chromosome 25 has been further added to the sex chromosomes in monk parakeet. Together, the combination of our genomic and cytogenetic analyses characterizes the complex evolutionary history of chromosomal rearrangements and sex chromosomes in parrots

Bioengineering of a human whole tooth: progress and challenge

A major challenge in stem cell-based bioengineering of an implantable human tooth is to identify appropriate sources of postnatal stem cells that are odontogenic competent as the epithelial component due to the lack of enamel epithelial cells in adult teeth. In a recent issue (2013, 2:6) of Cell Regeneration, Cai and colleagues reported that epithelial sheets derived from human induced pluripotent stem cells (iPSCs) can functionally substitute for tooth germ epithelium to regenerate tooth-like structures, providing an appealing stem cell source for future human tooth regeneration

High-Bandwidth Hysteresis Compensation of Piezoelectric Actuators via Multilayer Feedforward Neural Network Based Inverse Hysteresis Modeling

This paper proposes a feedforward and feedback combined hysteresis compensation method for a piezoelectric actuator (PEA) based on the multi-layer feedforward neural network (MFNN) inverse model. Under the scheme of direct inverse modeling, the MFNN is utilized as the feedforward hysteresis compensator, which can be directly identified from the measurements. The high modeling accuracy and high robustness of the MFNN help to increase the bandwidth of the closed-loop system. Experiments are conducted on a commercial PEA so as to verify the effectiveness of the proposed method. The superimposition of two sinusoidal signals is found to be efficient for the training of the MFNN. Closed-loop trajectory tracking experiments demonstrate that the bandwidth can be increased up to 1000 Hz and the maximum deviation can be maintained closed to the noise level. Meanwhile, there are only two parameters to be tuned in the proposed method, which guarantees ease of use for the inexperienced users. The proposed method successfully realizes high-precision hysteresis compensation performance across a wider frequency range

Active Model-Based Hysteresis Compensation and Tracking Control of Pneumatic Artificial Muscle

The hysteretic nonlinearity of pneumatic artificial muscle (PAM) is the main factor that degrades its tracking accuracy. This paper proposes an efficient hysteresis compensation method based on the active modeling control (AMC). Firstly, the Bouc&ndash;Wen model is adopted as the reference model to describe the hysteresis of the PAM. Secondly, the modeling errors are introduced into the reference model, and the unscented Kalman filter is used to estimate the state of the system and the modeling errors. Finally, a hysteresis compensation strategy is designed based on AMC. The compensation performances of the nominal controller with without AMC were experimentally tested on a PAM. The experimental results show that the proposed controller is more robust when tracking different types of trajectories. In the transient, both the overshoot and oscillation can be successfully attenuated, and fast convergence is achieved. In the steady-state, the proposed controller is more robust against external disturbances and measurement noise. The proposed controller is effective and robust in hysteresis compensation, thus improving the tracking performance of the PAM