Drp1 regulates transcription of ribosomal protein genes in embryonic hearts.

Mitochondrial dysfunction causes severe congenital cardiac abnormalities and prenatal/neonatal lethality. The lack of sufficient knowledge regarding how mitochondrial abnormalities affect cardiogenesis poses a major barrier for the development of clinical applications that target mitochondrial deficiency-induced inborn cardiomyopathies. Mitochondrial morphology, which is regulated by fission and fusion, plays a key role in determining mitochondrial activity. Dnm1l encodes a dynamin-related GTPase, Drp1, which is required for mitochondrial fission. To investigate the role of Drp1 in cardiogenesis during the embryonic metabolic shift period, we specifically inactivated Dnm1l in second heart field-derived structures. Mutant cardiomyocytes in the right ventricle (RV) displayed severe defects in mitochondrial morphology, ultrastructure and activity. These defects caused increased cell death, decreased cell survival, disorganized cardiomyocytes and embryonic lethality. By characterizing this model, we reveal an AMPK-SIRT7-GABPB axis that relays the reduced cellular energy level to decrease transcription of ribosomal protein genes in cardiomyocytes. We therefore provide the first genetic evidence in mouse that Drp1 is essential for RV development. Our research provides further mechanistic insight into how mitochondrial dysfunction causes pathological molecular and cellular alterations during cardiogenesis.

Differential requirement for DICER1 activity during the development of mitral and tricuspid valves.

Mitral and tricuspid valves are essential for unidirectional blood flow in the heart. They are derived from similar cell sources, and yet congenital dysplasia affecting both valves is clinically rare, suggesting the presence of differential regulatory mechanisms underlying their development. Here, we specifically inactivated Dicer1 in the endocardium during cardiogenesis and found that Dicer1 deletion caused congenital mitral valve stenosis and regurgitation, whereas it had no impact on other valves. We showed that hyperplastic mitral valves were caused by abnormal condensation and extracellular matrix (ECM) remodeling. Our single-cell RNA sequencing analysis revealed impaired maturation of mesenchymal cells and abnormal expression of ECM genes in mutant mitral valves. Furthermore, expression of a set of miRNAs that target ECM genes was significantly lower in tricuspid valves compared to mitral valves, consistent with the idea that the miRNAs are differentially required for mitral and tricuspid valve development. We thus reveal miRNA-mediated gene regulation as a novel molecular mechanism that differentially regulates mitral and tricuspid valve development, thereby enhancing our understanding of the non-association of inborn mitral and tricuspid dysplasia observed clinically.

Fibrotic Matrix Induces Mesenchymal Transformation of Epithelial Cells in Oral Submucous Fibrosis.

Oral submucous fibrosis (OSF) is a potentially malignant disorder of the oral mucosa; however, whether and how the fibrotic matrix of OSF is involved in the malignant transformation of epithelial cells remains unknown. Herein, oral mucosa tissue from patients with OSF, OSF rat models, and their controls were used to observe the extracellular matrix changes and epithelial-mesenchymal transformation (EMT) in fibrotic lesions. Compared with controls, oral mucous tissues from patients with OSF showed an increased number of myofibroblasts, a decreased number of blood vessels, and increased type I and type III collagen levels. In addition, the oral mucous tissues from humans and OSF rats showed increased stiffness, accompanied by increased EMT activities of epithelial cells. The EMT activities of stiff construct-cultured epithelial cells were increased significantly by exogenous piezo-type mechanosensitive ion channel component 1 (Piezo1) activation, and decreased by yes-associated protein (YAP) inhibition. During ex vivo implantation, oral mucosal epithelial cells of the stiff group showed increased EMT activities and increased levels of Piezo1 and YAP compared with those in the sham and soft groups. These results indicate that increased stiffness of the fibrotic matrix in OSF led to increased proliferation and EMT of mucosal epithelial cells, in which the Piezo1-YAP signal transduction is important.

Activation of a novel α2AAR-spinophilin-cofilin axis determines the effect of α2 adrenergic drugs on fear memory reconsolidation.

Posttraumatic stress disorder (PTSD) after the pandemic has emerged as a major neuropsychiatric component of post-acute COVID-19 syndrome, yet the current pharmacotherapy for PTSD is limited. The use of adrenergic drugs to treat PTSD has been suggested; however, it is hindered by conflicting clinical results and a lack of mechanistic understanding of drug actions. Our studies, using both genetically modified mice and human induced pluripotent stem cell-derived neurons, reveal a novel α2A adrenergic receptor (α2AAR)-spinophilin-cofilin axis in the hippocampus that is critical for regulation of contextual fear memory reconsolidation. In addition, we have found that two α2 ligands, clonidine and guanfacine, exhibit differential abilities in activating this signaling axis to disrupt fear memory reconsolidation. Stimulation of α2AAR with clonidine, but not guanfacine, promotes the interaction of the actin binding protein cofilin with the receptor and with the dendritic spine scaffolding protein spinophilin to induce cofilin activation at the synapse. Spinophilin-dependent regulation of cofilin is required for clonidine-induced disruption of contextual fear memory reconsolidation. Our results inform the interpretation of differential clinical observations of these two drugs on PTSD and suggest that clonidine could provide immediate treatment for PTSD symptoms related to the current pandemic. Furthermore, our study indicates that modulation of dendritic spine morphology may represent an effective strategy for the development of new pharmacotherapies for PTSD.

Fibrocyte: A missing piece in the pathogenesis of fibrous epulis.

OBJECTIVES: To explore the role of fibrocytes in the recurrence and calcification of fibrous epulides. METHODS: Different subtypes of fibrous epulides and normal gingival tissue specimens were first collected for histological and immunofluorescence analyses to see if fibrocytes were present and whether they differentiated into myofibroblasts and osteoblasts upon stimulated by transforming growth factor-ß1 (TGF-ß1). Electron microscopy and elemental analysis were used to characterize the extracellular microenvironment in different subtypes of fibrous epulides. Human peripheral blood mononuclear cells (PBMCs) were subsequently isolated from in vitro models to mimic the microenvironment in fibrous epulides to identify whether TGF-ß1 as well as the calcium and phosphorus ion concentration in the extracellular matrix (ECM) of a fibrous epulis trigger fibrocyte differentiation. RESULTS: Fibrous epulides contain fibrocytes that accumulate in the local inflammatory environment and have the ability to differentiate into myofibroblasts or osteoblasts. TGF-ß1 promotes fibrocytes differentiation into myofibroblasts in a concentration-dependent manner, while TGF-ß1 stimulates the fibrocytes to differentiate into osteoblasts when combined with a high calcium and phosphorus environment. CONCLUSIONS: Our study revealed fibrocytes play an important role in the fibrogenesis and osteogenesis in fibrous epulis, and might serve as a therapeutic target for the inhibition of recurrence of fibrous epulides.

Ion Steric Effect Induces Giant Enhancement of Thermoelectric Conversion in Electrolyte-Filled Nanochannels.

Ionic thermoelectricity in nanochannels has received increasing attention because of its advantages, such as high Seebeck coefficient and low cost. However, most studies have focused on dilute simple electrolytes that neglect the effects of finite ion sizes and short-range electrostatic correlation. Here, we reveal a new thermoelectric mechanism arising from the coupling of the ion steric effect due to finite ion sizes and ion thermodiffusion in electric double layers, using both theoretical and numerical methods. We show that this mechanism can significantly enhance the thermoelectric response in nanoconfined electrolytes depending on the properties of electrolytes and nanochannels. Compared to the previously known mechanisms, the new mechanism can increase the Seebeck coefficient by 100% or even 1 order of magnitude enhancement under optimal conditions. Moreover, we demonstrate that the short-range electrostatic correlation can help preserve the Seebeck coefficient enhancement in a weaker confinement or in more concentrated electrolytes.

Design and fabrication of large-mode-area multicore chalcogenide fiber with low bending loss.

Multicore fiber (MCF) has a larger mode-area (LMA) compared to traditional single-core fiber, making it easy to get a mode area of more than 3000 µm2 with an optimized MCF structure. Here, a fine-structured 19-core fiber based on chalcogenide glass was fabricated using a combined method involving extrusion, drilling, and rod-in-tube for the first time. The fiber has a minimum transmission loss of 1.8 dB/m at 6.7 µm. When the bending radius exceeds 6 cm, a low bending loss of about 0.6 dB appears, and the experimental data are in good agreement with the simulation results. In addition, the supermode characteristics of the 19-core fiber are analyzed from both perspectives of simulation and experiment, and these results are perfectly in good agreement. We believe it opens a new way to develop high-power and bend-resisting fiber with such kind of multicore structure.

Orthodenticle Homeobox OTX1 Promotes Papillary Thyroid Carcinoma Progression and Is a Potential Prognostic Biomarker.

Papillary thyroid carcinoma (PTC) is the most common type of thyroid neoplasms, characterized by evidence of follicular cell differentiation. Orthodenticle homeobox 1 (OTX1) is a transcription factor which has been implicated in numerous diseases, including malignancies. The objective of this research was to explore the function of OTX1 in PTC. Immunohistochemistry (IHC) was employed to determine the protein level of OTX1 in PTC specimens. Cell viability was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Furthermore, a xenograft model on nude mice was established to investigate in vivo effects of OTX1. Our results revealed that OTX1 was significantly upregulated within specific PTC tissues and was remarkably correlated with unfavorable clinical outcomes in PTC. Silencing OTX1 resulted in a significant inhibition in cell viability and suppressed cell proliferation. In addition, in vivo experiments demonstrated that OTX1 silencing resulted in a significant suppression of tumor growth in nude mice. Collectively, these results suggest that OTX1 may play crucial roles in promoting PTC progression.

Expanding the reproductive organ phenotype of CHD7-spectrum disorder.

CHD7 disorder is a multiple congenital anomaly syndrome with a highly variable phenotypic spectrum, and includes CHARGE syndrome. Internal and external genital phenotypes frequently seen in CHD7 disorder include cryptorchidism and micropenis in males, and vaginal hypoplasia in females, both thought to be secondary to hypogonadotropic hypogonadism. Here, we report 14 deeply phenotyped individuals with known CHD7 variants (9 pathogenic/likely pathogenic and 5 VOUS) and a range of reproductive and endocrine phenotypes. Reproductive organ anomalies were observed in 8 of 14 individuals and were more commonly noted in males (7/7), most of whom presented with micropenis and/or cryptorchidism. Kallmann syndrome was commonly observed among adolescents and adults with CHD7 variants. Remarkably, one 46,XY individual presented with ambiguous genitalia, cryptorchidism with Müllerian structures including uterus, vagina and fallopian tubes, and one 46,XX female patient presented with absent vagina, uterus and ovaries. These cases expand the genital and reproductive phenotype of CHD7 disorder to include two individuals with genital/gonadal atypia (ambiguous genitalia), and one with Müllerian aplasia.

A simplified mid-infrared anti-resonant chalcogenide fiber with fewest resonant peaks.

High-power laser delivery in the mid-infrared via hollow-core fibers is attractive, but it is too difficult to be fabricated using chalcogenide glasses. Here, we designed a mid-infrared hollow-core anti-resonant chalcogenide fiber (HC-ARCF) with a simplified Kagome cladding micro-structure for the first time. Then, the fiber was firstly fabricated through a precision mechanical drilling and pressured fiber drawing method. Ultra-thin walls of 2µm in the fiber lead to the fewest resonance peaks in the 2-5µm among all reported HC-ARCFs. All the fundamental mode, the second-order mode, tube mode and node mode in the fiber were excited and observed at 1550 nm. The power and spectral properties of the core and cladding of HC-ARCF are studied for the first time. The fiber can deliver high-power of 4.84 W without damage with core-coupling, while the threshold of the node in the cladding is only 3.5 W. A broadening of the output spectrum from 1.96 to 2.41µm due to the high nonlinearity at the node was successfully observed under short-pulse laser pumping at 2µm. The potentials of the fiber used for mid-infrared high-power laser delivery via core, or nonlinear laser generation via node, were thus demonstrated.

CHD7 regulates cardiovascular development through ATP-dependent and -independent activities.

CHD7 encodes an ATP-dependent chromatin remodeling factor. Mutation of this gene causes multiple developmental disorders, including CHARGE (Coloboma of the eye, Heart defects, Atresia of the choanae, Retardation of growth/development, Genital abnormalities, and Ear anomalies) syndrome, in which conotruncal anomalies are the most prevalent form of heart defects. How CHD7 regulates conotruncal development remains unclear. In this study, we establish that deletion of Chd7 in neural crest cells (NCCs) causes severe conotruncal defects and perinatal lethality, thus providing mouse genetic evidence demonstrating that CHD7 cell-autonomously regulates cardiac NCC development, thereby clarifying a long-standing controversy in the literature. Using transcriptomic analyses, we show that CHD7 fine-tunes the expression of a gene network that is critical for cardiac NCC development. To gain further molecular insights into gene regulation by CHD7, we performed a protein-protein interaction screen by incubating recombinant CHD7 on a protein array. We find that CHD7 directly interacts with several developmental disorder-mutated proteins including WDR5, a core component of H3K4 methyltransferase complexes. This direct interaction suggested that CHD7 may recruit histone-modifying enzymes to target loci independently of its remodeling functions. We therefore generated a mouse model that harbors an ATPase-deficient allele and demonstrates that mutant CHD7 retains the ability to recruit H3K4 methyltransferase activity to its targets. Thus, our data uncover that CHD7 regulates cardiovascular development through ATP-dependent and -independent activities, shedding light on the etiology of CHD7-related congenital disorders. Importantly, our data also imply that patients carrying a premature stop codon versus missense mutations will likely display different molecular alterations; these patients might therefore require personalized therapeutic interventions.

mTOR deletion in neural crest cells disrupts cardiac outflow tract remodeling and causes a spectrum of cardiac defects through the mTORC1 pathway.

A critical cell type participating in cardiac outflow tract development is a subpopulation of the neural crest cells, the cardiac neural crest cells (NCCs), whose defect causes a spectrum of cardiovascular abnormalities. Accumulating evidence indicates that mTOR, which belongs to the PI3K-related kinase family and impacts multiple signaling pathways in a variety of contexts, plays a pivotal role for NCC development. Here, we investigated functional roles of mTOR for cardiac neural crest development using several lines of mouse genetic models. We found that disruption of mTOR caused NCC defects and failure of cardiac outflow tract separation, which resulted in a spectrum of cardiac defects including persistent truncus arteriosus, ventricular septal defect and ventricular wall defect. Specifically, mutant neural crest cells showed reduced migration into the cardiac OFT and prematurely exited the cell cycle. A number of critical factors and fundamental signaling pathways, which are important for neural crest and cardiomyocyte development, were impaired. Moreover, actin dynamics was disrupted by mTOR deletion. Finally, by phenotyping the neural crest Rptor and Rictor knockout mice respectively, we demonstrate that mTOR acts principally through the mTORC1 pathway for cardiac neural crest cells. Altogether, these data established essential roles of mTOR for cardiac NCC development and imply that dysregulation of mTOR in NCCs may underline a spectrum of cardiac defects.

Single-mode suspended large-core chalcohalide fiber with a low zero-dispersion wavelength for supercontinuum generation.

Chalcogenide glass possesses outstanding advantages, such as supercontinuum generation, but its nonlinear applications were limited by large zero-dispersion wavelength (ZDW). Traditional suspended-core fibers can shift the ZDW to near IR with a tiny core size of less than 5 µm but a large evanescent wave loss exists in these fibers. In this paper, we prepared a novel suspended-core fiber (SCF) based on chalcohalide glasses for the first time via the extrusion method, in which the ZDW of the fundamental mode in the fiber with a core size of larger than 30 µm was successfully shifted to 2.6 µm. We also calculated confinement loss (CL) of propagation modes and fundamental mode energy ratio in the fiber. We found that the minimum CL ratio of the high order modes (LP11) to the CL of the fundamental mode is 124, indicating that the single-mode operation condition is satisfied when the wavelength is more than 4.6 µm. The lowest transmission loss is 1.2 dB/m at 6.5 µm. An ultra-broad supercontinuum spectrum, covering from 1.6 to 12 µm was generated in this suspended-core fiber pumped by a 5 µm femtosecond laser. Such a wide SC in the chalcogenide SCF is due to the large core size. All these results demonstrate the potential to use the large core SCF in the application of a mid-IR laser.

Se-H-free As2Se3 fiber and its spectral applications in the mid-infrared.

The complete removal of the impurities like Se-H in Se-based chalcogenide glasses has been challenging in the development of highly transparent chalcogenide glass fiber. In this paper, several purification methods, including dynamic distillation, static distillation, and combined distillation method, were adopted with an aim of purifying arsenic selenide glass with ultra-low content of the impurities. The experimental results demonstrated that the Se-H can be completely eliminated in the arsenic selenide glass host and fiber without the introduction of any chloride. We further explored the applications of such low loss and Se-H-free chalcogenide glass fiber in the mid-infrared. It was found that, using such a Se-H free fiber, a flattened supercontinuum spectrum above the -30 dB level from 1.2 to 13 µm was generated from the Se-H free fiber with a 5.5 µm laser pumping. The sensitivity was found to be improved 5.1 times for CO2 gas in the 3 to 6 µm wavelength range.

Structural features and electrostatic energy storage of electric double layers in confined polyelectrolyte solutions under low-salt conditions.

An electric double layer (EDL) in a polyelectrolyte solution plays a crucial role in diverse fields ranging from physical and life sciences to modern technologies. Due to the nonnegligible excluded volume effects, chain connectivity and complex intermolecular interactions, the EDLs in (confined) polyelectrolyte solutions display distinct features compared to those in simple electrolyte solutions. Here, we conducted a systematic study on the characteristics of EDLs in confined polyelectrolyte solutions for salt-free and low salt concentration systems using self-consistent field theory. Results suggest that the characteristic length scales measuring the EDL structures are different for positively and negatively charged surfaces. The former is the same as in the electrolyte solutions, while the latter is smaller due to the accumulation of oppositely charged polyelectrolytes near the surface. Furthermore, for low surface charge densities, a scaling law for the electrostatic energy stored in polyelectrolyte EDLs (in units of mJ m-2) was found to be U ∝ |σ|ν with ν ∼ 2-2.7, which differs from the electrolyte EDLs with ν ∼ 2; however, such a scaling law breaks down for high surface charge densities.

LncRNA FOXD3-AS1 aggravates myocardial ischemia/reperfusion injury by inactivating the Redd1/AKT/GSK3ß/Nrf2 signaling pathway via the miR-128/TXNIP axis.

Long noncoding RNA forkhead box D3-antisense RNA 1 (FOXD3-AS1) is associated with cardiovascular diseases, but its roles in myocardial ischemia/reperfusion (I/R) injury and the related signaling pathway have not been fully reported. We aimed to investigate the roles and mechanism of action of FOXD3-AS1 in myocardial I/R injury. An in vivo myocardial I/R injury mouse model and an in vitro hypoxia/reoxygenation (H/R) cardiomyocyte model was established. Quantitative reverse transcription-polymerase chain reaction, western blotting, and immunofluorescent assays were performed to examine the expression levels of FOXD3-AS1, microRNA (miR)-128, thioredoxin-interacting protein/regulation of development and DNA damage response 1/protein kinase B/glycogen synthase kinase 3ß/nuclear factor erythroid 2-related factor 2 (TXNIP/Redd1/AKT/GSK3ß/Nrf2) pathway-related proteins and apoptosis-related proteins. The interactions between FOXD3-AS1 and miR-128 and miR-128 and TXNIP were analyzed by Spearman's correlation test, predicted by ENCORI, and verified by dual-luciferase reporter assay. In addition, the levels of cardiac injury markers and oxidative stress markers were evaluated by corresponding kits. Cell Counting Kit-8 assays and flow cytometry were performed to assess cell viability and apoptosis. Hematoxylin and eosin staining was applied to observe the effect of FOXD3-AS1 on the morphology of myocardial I/R injured tissues. The results showed that the FOXD3-AS1 and TXNIP were highly expressed, whereas miR-128 was expressed at low levels in I/R myocardial tissues and H/R-induced H9c2 cells. FOXD3-AS1 directly targeted miR-128 to reduce its expression. TXNIP was confirmed as a downstream target of miR-128. Knockdown of FOXD3-AS1 led to the alleviation of I/R injury in vivo and in vitro. FOXD3-AS1 enhanced the expression of TXNIP by sponging miR-128, which inhibited the Redd1/AKT/GSK3ß/Nrf2 pathway. Both inhibition of miR-128 and overexpression of TXNIP reversed the cardioprotective effect of FOXD3-AS1 small interfering RNA in H/R-induced H9c2 cells.

Pathological mechanism of chondrocytes and the surrounding environment during osteoarthritis of temporomandibular joint.

Temporomandibular joint (TMJ) osteoarthritis is a common chronic degenerative disease of the TMJ. In order to explore its aetiology and pathological mechanism, many animal models and cell models have been constructed to simulate the pathological process of TMJ osteoarthritis. The main pathological features of TMJ osteoarthritis include chondrocyte death, extracellular matrix (ECM) degradation and subchondral bone remodelling. Chondrocyte apoptosis accelerates the destruction of cartilage. However, autophagy has a protective effect on condylar chondrocytes. Degradation of ECM not only changes the properties of cartilage but also affects the phenotype of chondrocytes. The loss of subchondral bone in the early stages of TMJ osteoarthritis plays an aetiological role in the onset of osteoarthritis. In recent years, increasing evidence has suggested that chondrocyte hypertrophy and endochondral angiogenesis promote TMJ osteoarthritis. Hypertrophic chondrocytes secrete many factors that promote cartilage degeneration. These chondrocytes can further differentiate into osteoblasts and osteocytes and accelerate cartilage ossification. Intrachondral angiogenesis and neoneurogenesis are considered to be important triggers of arthralgia in TMJ osteoarthritis. Many molecular signalling pathways in endochondral osteogenesis are responsible for TMJ osteoarthritis. These latest discoveries in TMJ osteoarthritis have further enhanced the understanding of this disease and contributed to the development of molecular therapies. This paper summarizes recent cognition on the pathogenesis of TMJ osteoarthritis, focusing on the role of chondrocyte hypertrophy degeneration and cartilage angiogenesis.

mTOR acts as a pivotal signaling hub for neural crest cells during craniofacial development.

mTOR is a highly conserved serine/threonine protein kinase that is critical for diverse cellular processes in both developmental and physiological settings. mTOR interacts with a set of molecules including Raptor and Rictor to form two distinct functional complexes, namely the mTORC1 and mTORC2. Here, we used novel genetic models to investigate functions of the mTOR pathway for cranial neural crest cells (NCCs), which are a temporary type of cells arising from the ectoderm layer and migrate to the pharyngeal arches participating craniofacial development. mTOR deletion elicited a proliferation deficit and excessive apoptosis of post-migratory NCCs, leading to growth arrest of the facial primordia along with midline orofacial clefts. Furthermore, NCC differentiation was impaired. Thus, NCC derivatives, such as skeletons, vasculatures and neural tissues were either rudimentary or malformed. We further demonstrate that disruption of mTOR caused P53 hyperactivity and cell cycle arrest in cranial NCCs, and lowering P53 activity by one copy reduction attenuated the severity of craniofacial phenotype in NCC-mTOR knockout mice. Remarkably, NCC-Rptor disruption caused a spectrum of defects mirroring that of the NCC-mTOR deletion, whereas NCC-Rictor disruption only caused a mild craniofacial phenotype compared to the mTOR and Rptor conditional knockout models. Altogether, our data demonstrate that mTOR functions mediated by mTORC1 are indispensable for multiple processes of NCC development including proliferation, survival, and differentiation during craniofacial morphogenesis and organogenesis, and P53 hyperactivity in part accounts for the defective craniofacial development in NCC-mTOR knockout mice.

Poly-Adenine-Based Spherical Nucleic Acids for Efficient Live-Cell MicroRNA Capture.

Direct delivery of exogenous non-coding nucleic acids into living cells has attracted intense interest in biological applications. However, the cell entry efficiency and target capture ability remain to be improved. Herein, we report a method for compartmenting the nucleic acids on the surface of poly-adenine-based spherical nucleic acids (polyA-SNAs) for efficient capture of oncogenic microRNAs (miRNAs) in living cells. We find that polyA-SNAs exhibit high cell entry efficiency, which is insensitive to the configuration of the anti-miRNA sequences. By programming the length of polyAs, we precisely engineered the spatial configuration of the anti-miRNA sequences in polyA-SNAs. Compartmentalized polyA-SNAs bind to miRNAs with improved capture ability as compared to densely compacted SNAs. We further demonstrate that polyA-SNAs serve as high-efficacy miRNA sponges for capturing oncogenic miRNAs both in living cells and in mice. The efficient inhibition of miRNAs results in significant suppression of tumor growth.

SEMA6D regulates perinatal cardiomyocyte proliferation and maturation in mice.

Cardiomyocytes undergo dramatic changes during the fetal to neonatal transition stage to adapt to the new environment. The molecular and genetic mechanisms regulating these changes remain elusive. In this study, we showed Sema6D as a novel signaling molecule regulating perinatal cardiomyocyte proliferation and maturation. SEMA6D is a member of the Semaphorin family of signaling molecules. To reveal its function during cardiogenesis, we specifically inactivated Sema6D in embryonic cardiomyocytes using a conditional gene deletion approach. All mutant animals showed hypoplastic myocardial walls in neonatal hearts due to reduced cell proliferation. We further revealed that expression of MYCN and its downstream cell cycle regulators is impaired in late fetal hearts in which Sema6D is deleted, suggesting that SEMA6D acts through MYCN to regulate cardiomyocyte proliferation. In early postnatal mutant hearts, expression of adult forms of sarcomeric proteins is increased, while expression of embryonic forms is decreased. These data collectively suggest that SEMA6D is required to maintain late fetal/early neonatal cardiomyocytes at a proliferative and less mature status. Deletion of Sema6D in cardiomyocytes led to reduced proliferation and accelerated maturation. We further examined the consequence of these defects through echocardiographic analysis. Embryonic heart deletion of Sema6D significantly impaired the cardiac contraction of male adult hearts, while having a minor effect on female mutant hearts, suggesting that the effect of Sema6D-deletion in adult hearts is sex dependent.