Loss of myocardial Hey2/Hrt2 function disrupts rightward shift of atrioventricular cushion tissue and causes tricuspid atresia.

BACKGROUND: Endocardial cushion tissue is primordia of the valves and septa of the adult heart, and its malformation causes various congenital heart diseases (CHDs). Tricuspid atresia (TA) is defined as congenital absence or agenesis of the tricuspid valve caused by endocardial cushion defects. However, little is known about what type of endocardial cushion defect causes TA. RESULTS: Using three-dimensional volume rendering image analysis, we demonstrated morphological changes of endocardial cushion tissue in developing Hey2/Hrt2 KO mouse embryos that showed malformation of the tricuspid valve, which resembled human TA at neonatal period. In control embryos, atrioventricular (AV) endocardial cushion tissues showed rightward shift to form a tricuspid valve. However, the rightward shift of endocardial cushion tissue was disrupted in Hey2/Hrt2 KO embryos, leading to the misalignment of AV cushions. We also found that muscular tissue filled up the space between the right atrium and ventricle, resulting in the absence of the tricuspid valve. Moreover, analysis using tissue-specific conditional KO mice showed that HEY2/HRT2-expressing myocardium may physically regulate the AV shift. CONCLUSION: Disruption of rightward cushion movement is an initial cue of TA phenotype, and myocardial HEY2/HRT2 is necessary for the regulation of proper alignment of AV endocardial cushion tissue.

Gestational diabetes in mice induces hematopoietic memory that affects the long-term health of the offspring.

Gestational diabetes is a common medical complication of pregnancy that is associated with adverse perinatal outcomes and an increased risk of metabolic diseases and atherosclerosis in adult offspring. The mechanisms responsible for this delayed pathological transmission remain unknown. In mouse models, we found that the development of atherosclerosis in adult offspring born to diabetic pregnancy can be in part linked to hematopoietic alterations. Although they do not show any gross metabolic disruptions, the adult offspring maintain hematopoietic features associated with diabetes, indicating the acquisition of a lasting diabetic hematopoietic memory. We show that the induction of this hematopoietic memory during gestation relies on the activity of the advanced glycation end product receptor (AGER) and the nucleotide binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, which lead to increased placental inflammation. In adult offspring, we find that this memory is associated with DNA methyltransferase 1 (DNMT1) upregulation and epigenetic changes in hematopoietic progenitors. Together, our results demonstrate that the hematopoietic system can acquire a lasting memory of gestational diabetes and that this memory constitutes a pathway connecting gestational health to adult pathologies.

PRDM16 regulates arterial development and vascular integrity.

Proper vascular formation is regulated by multiple signaling pathways. The vascular endothelial growth factor (VEGF) signaling promotes endothelial proliferation. Notch and its downstream targets act to lead endothelial cells toward an arterial fate through regulation of arterial gene expression. However, the mechanisms of how endothelial cells (ECs) in the artery maintain their arterial characteristics remain unclear. Here, we show that PRDM16 (positive regulatory domain-containing protein 16), a zinc finger transcription factor, is expressed in arterial ECs, but not venous ECs in developing embryos and neonatal retinas. Endothelial-specific deletion of Prdm16 induced ectopic venous marker expression in the arterial ECs and reduced vascular smooth muscle cell (vSMC) recruitment around arteries. Whole-genome transcriptome analysis using isolated brain ECs show that the expression of Angpt2 (encoding ANGIOPOIETIN2, which inhibits vSMC recruitment) is upregulated in the Prdm16 knockout ECs. Conversely, forced expression of PRDM16 in venous ECs is sufficient to induce arterial gene expression and repress the ANGPT2 level. Together, these results reveal an arterial cell-autonomous function for PRDM16 in suppressing venous characteristics in arterial ECs.

Nuclear condensates of YAP fusion proteins alter transcription to drive ependymoma tumourigenesis.

Nuclear localization of HIPPO-YAP fusion proteins has been implicated in supratentorial ependymoma development. Here, unexpectedly, we find that liquid-liquid phase separation, rather than nuclear localization, of recurrent patient-derived YAP fusions, YAP-MAMLD1 and C11ORF95-YAP, underlies ependymoma tumourigenesis from neural progenitor cells. Mutagenesis and chimaera assays demonstrate that an intrinsically disordered region promotes oligomerization of the YAP fusions into nuclear, puncta-like, membrane-less condensates. Oligomerization and nuclear condensates induced by YAP fusion with a coiled-coil domain of transcriptional activator GCN4 also promote ependymoma formation. YAP-MAMLD1 concentrates transcription factors and co-activators, including BRD4, MED1 and TEAD, in condensates while excluding transcriptional repressive PRC2, and induces long-range enhancer-promoter interactions that promote transcription and oncogenic programmes. Blocking condensate-mediated transcriptional co-activator activity inhibits tumourigenesis, indicating a critical role of liquid phase separation for YAP fusion oncogenic activity in ependymoma. YAP fusions containing the intrinsically disordered region features are common in human tumours, suggesting that nuclear condensates could be targeted to treat YAP-fusion-induced cancers.

Inhibition of ß1-AR/Gαs signaling promotes cardiomyocyte proliferation in juvenile mice through activation of RhoA-YAP axis.

The regeneration potential of the mammalian heart is incredibly limited, as cardiomyocyte proliferation ceases shortly after birth. ß-adrenergic receptor (ß-AR) blockade has been shown to improve heart functions in response to injury; however, the underlying mechanisms remain poorly understood. Here, we inhibited ß-AR signaling in the heart using metoprolol, a cardio-selective ß blocker for ß1-adrenergic receptor (ß1-AR) to examine its role in heart maturation and regeneration in postnatal mice. We found that metoprolol enhanced cardiomyocyte proliferation and promoted cardiac regeneration post myocardial infarction, resulting in reduced scar formation and improved cardiac function. Moreover, the increased cardiomyocyte proliferation was also induced by the genetic deletion of Gnas, the gene encoding G protein alpha subunit (Gαs), a downstream effector of ß-AR. Genome wide transcriptome analysis revealed that the Hippo-effector YAP, which is associated with immature cardiomyocyte proliferation, was upregulated in the cardiomyocytes of ß-blocker treated and Gnas cKO hearts. Moreover, the increased YAP activity is modulated by RhoA signaling. Our pharmacological and genetic studies reveal that ß1-AR-Gαs-YAP signaling axis is involved in regulating postnatal cardiomyocyte proliferation. These results suggest that inhibiting ß-AR-Gαs signaling promotes the regenerative capacity and extends the cardiac regenerative window in juvenile mice by activating YAP-mediated transcriptional programs.

Modeling Human Bile Acid Transport and Synthesis in Stem Cell-Derived Hepatocytes with a Patient-Specific Mutation.

The bile salt export pump (BSEP) is responsible for the export of bile acid from hepatocytes. Impaired transcellular transport of bile acids in hepatocytes with mutations in BSEP causes cholestasis. Compensatory mechanisms to regulate the intracellular bile acid concentration in human hepatocytes with BSEP deficiency remain unclear. To define pathways that prevent cytotoxic accumulation of bile acid in hepatocytes, we developed a human induced pluripotent stem cell-based model of isogenic BSEP-deficient hepatocytes in a Transwell culture system. Induced hepatocytes (i-Heps) exhibited defects in the apical export of bile acids but maintained a low intracellular bile acid concentration by inducing basolateral export. Modeling the autoregulation of bile acids on hepatocytes, we found that BSEP-deficient i-Heps suppressed de novo bile acid synthesis using the FXR pathway via basolateral uptake and export without apical export. These observations inform the development of therapeutic targets to reduce the overall bile acid pool in patients with BSEP deficiency.

YAP/TAZ-CDC42 signaling regulates vascular tip cell migration.

Angiogenesis and vascular remodeling are essential for the establishment of vascular networks during organogenesis. Here we show that the Hippo signaling pathway effectors YAP and TAZ are required, in a gene dosage-dependent manner, for the proliferation and migration of vascular endothelial cells (ECs) during retinal angiogenesis. Intriguingly, nuclear translocation of YAP and TAZ induced by Lats1/2-deletion blocked endothelial migration and phenocopied Yap/Taz-deficient mutants. Furthermore, overexpression of a cytoplasmic form of YAP (YAPS127D) partially rescued the migration defects caused by loss of YAP and TAZ function. Finally, we found that cytoplasmic YAP positively regulated the activity of the small GTPase CDC42, deletion of which caused severe defects in endothelial migration. These findings uncover a previously unrecognized role of cytoplasmic YAP/TAZ in promoting cell migration by activating CDC42 and provide insight into how Hippo signaling in ECs regulates angiogenesis.

A reciprocal regulatory loop between TAZ/YAP and G-protein Gαs regulates Schwann cell proliferation and myelination.

Schwann cell (SC) myelination in the peripheral nervous system is essential for motor function, and uncontrolled SC proliferation occurs in cancer. Here, we show that a dual role for Hippo effectors TAZ and YAP in SC proliferation and myelination through modulating G-protein expression and interacting with SOX10, respectively. Developmentally regulated mutagenesis indicates that TAZ/YAP are critical for SC proliferation and differentiation in a stage-dependent manner. Genome-wide occupancy mapping and transcriptome profiling reveal that nuclear TAZ/YAP promote SC proliferation by activating cell cycle regulators, while targeting critical differentiation regulators in cooperation with SOX10 for myelination. We further identify that TAZ targets and represses Gnas, encoding Gαs-protein, which opposes TAZ/YAP activities to decelerate proliferation. Gnas deletion expands SC precursor pools and blocks peripheral myelination. Thus, the Hippo/TAZ/YAP and Gαs-protein feedback circuit functions as a fulcrum balancing SC proliferation and differentiation, providing insights into molecular programming of SC lineage progression and homeostasis.

Pharyngeal arch artery defects and lethal malformations of the aortic arch and its branches in mice deficient for the Hrt1/Hey1 transcription factor.

The aortic arch and major branch arteries are formed from the three pairs of pharyngeal arch arteries (PAAs) during embryonic development. Their morphological defects are clinically observed as isolated diseases, as a part of complicated cardiovascular anomalies or as a manifestation of multi-organ syndromes such as 22q11.2 deletion syndrome. Although numerous genes have been implicated in PAA formation and remodeling, detailed mechanisms remain poorly understood. Here we report that the mice null for Hrt1/Hey1, a gene encoding a downstream transcription factor of Notch and ALK1 signaling pathways, show perinatal lethality on the C57BL/6N, C57BL/6N × C57BL/6J or C57BL/6N × 129X1/SvJ background. Hrt1/Hey1 null embryos display abnormal development of the fourth PAA (PAA4), which results in congenital vascular defects including right-sided aortic arch, interruption of the aortic arch and aberrant origin of the right subclavian artery. Impaired vessel formation occurs randomly in PAA4 of Hrt1/Hey1 null embryos, which likely causes the variability of congenital malformations. Endothelial cells in PAA4 of null embryos differentiate normally but are structurally disorganized at embryonic day 10.5 and 11.5. Vascular smooth muscle cells are nearly absent in the structurally-defective PAA4, despite the appropriate migration of cardiac neural crest cells into the fourth pharyngeal arches. Endothelial expression of Jag1 is down-regulated in the structurally-defective PAA4 of null embryos, which may be one of the mechanisms underlying the suppression of vascular smooth muscle cell differentiation. While the direct downstream phenomena of the Hrt1/Hey1 deficiency remain to be clarified, we suggest that Hrt1/Hey1-dependent transcriptional regulation has an important role in PAA formation during embryonic development.

Impairment of endothelial-mesenchymal transformation during atrioventricular cushion formation in Tmem100 null embryos.

BACKGROUND: Endothelial-mesenchymal transformation (EndMT) is essential for endocardial cushion formation during cardiac morphogenesis. We recently identified Tmem100 as an endothelial gene indispensable for vascular development. In this study, we further investigated its roles for EndMT during atrioventricular canal (AVC) cushion formation. RESULTS: Tmem100 was expressed in AVC endocardial cells, and Tmem100 null embryos showed severe EndMT defect in the AVC cushions. While calcineurin-dependent suppression of vascular endothelial growth factor (VEGF) expression in the AVC myocardium is important for EndMT, significant up-regulation of Vegfa expression was observed in Tmem100 null heart. EndMT impaired in Tmem100 null AVC explants was partially but significantly restored by the expression of constitutively-active calcineurin A, suggesting dysregulation of myocardial calcineurin-VEGF signaling in Tmem100 null heart. Moreover, Tmem100 null endocardial cells in explant culture did not show EndMT in response to the treatment with myocardium-derived growth factors, transforming growth factor ß2 and bone morphogenetic protein 2, indicating involvement of an additional endocardial-specific abnormality in the mechanism of EndMT defect. The lack of NFATc1 nuclear translocation in endocardial cells of Tmem100 null embryos suggests impairment of endocardial calcium signaling. CONCLUSIONS: The Tmem100 deficiency causes EndMT defect during AVC cushion formation possibly via disturbance of multiple calcium-related signaling events.

An important role of endothelial hairy-related transcription factors in mouse vascular development.

The Hairy-related transcription factor family of Notch- and ALK1-downstream transcriptional repressors, called Hrt/Hey/Hesr/Chf/Herp/Gridlock, has complementary and indispensable functions for vascular development. While mouse embryos null for either Hrt1/Hey1 or Hrt2/Hey2 did not show early vascular phenotypes, Hrt1/Hey1; Hrt2/Hey2 double null mice (H1(ko) /H2(ko) ) showed embryonic lethality with severe impairment of vascular morphogenesis. It remained unclear, however, whether Hrt/Hey functions are required in endothelial cells or vascular smooth muscle cells. In this study, we demonstrate that mice with endothelial-specific deletion of Hrt2/Hey2 combined with global Hrt1/Hey1 deletion (H1(ko) /H2(eko) ) show abnormal vascular morphogenesis and embryonic lethality. Their defects were characterized by the failure of vascular network formation in the yolk sac, abnormalities of embryonic vascular structures and impaired smooth muscle cell recruitment, and were virtually identical to the H1(ko) /H2(ko) phenotypes. Among signaling molecules implicated in vascular development, Robo4 expression was significantly increased and activation of Src family kinases was suppressed in endothelial cells of H1(ko) /H2(eko) embryos. The present study indicates an important role of Hrt1/Hey1 and Hrt2/Hey2 in endothelial cells during early vascular development, and further suggests involvement of Robo4 and Src family kinases in the mechanisms of embryonic vascular defects caused by the Hrt/Hey deficiency.

Tmem100, an ALK1 receptor signaling-dependent gene essential for arterial endothelium differentiation and vascular morphogenesis.

Members of the transforming growth factor-ß superfamily play essential roles in various aspects of embryonic development and physiological organ function. Among them, bone morphogenetic protein (BMP) 9 and BMP10 regulate embryonic vascular development by activating their endothelial receptor ALK1 (activin receptor-like kinase 1, also called Acvrl1). ALK1-mediated intracellular signaling is implicated in the etiologies of human diseases, but their downstream functional proteins are largely unknown. In this study, we identified Tmem100, a gene encoding a previously uncharacterized intracellular transmembrane protein, to be an embryonic endothelium-enriched gene activated by BMP9 and BMP10 through the ALK1 receptor. Tmem100 null mice showed embryonic lethality due to impaired differentiation of arterial endothelium and defects of vascular morphogenesis, which phenocopied most of the vascular abnormalities observed with the Acvrl1/Alk1 deficiency. The activity of Notch- and Akt-mediated signaling, which is essential for vascular development, was down-regulated in Tmem100 null mice. Cre-mediated deletion of Tmem100 in endothelial cells was sufficient to recapitulate the null phenotypes. These data indicated that TMEM100 may play indispensable roles downstream of BMP9/BMP10-ALK1 signaling during endothelial differentiation and vascular morphogenesis.

Ectopic retinoic acid signaling affects outflow tract cushion development through suppression of the myocardial Tbx2-Tgfß2 pathway.

The progress of molecular genetics has enabled us to identify the genes responsible for congenital heart malformations. However, recent studies suggest that congenital heart diseases are induced not only by mutations in certain genes, but also by abnormal maternal factors. A high concentration of maternal retinoic acid (RA), the active derivative of vitamin A, is well known as a teratogenic agent that can cause developmental defects. Our previous studies have shown that the maternal administration of RA to mice within a narrow developmental window induces outflow tract (OFT) septum defects, a condition that closely resembles human transposition of the great arteries (TGA), although the responsible factors and pathogenic mechanisms of the TGA induced by RA remain unknown. We herein demonstrate that the expression of Tbx2 in the OFT myocardium is responsive to RA, and its downregulation is associated with abnormal OFT development. We found that RA could directly downregulate the Tbx2 expression through a functional retinoic acid response element (RARE) in the Tbx2 promoter region, which is also required for the initiation of Tbx2 transcription during OFT development. Tgfb2 expression was also downregulated in the RA-treated OFT region and was upregulated by Tbx2 in a culture system. Moreover, defective epithelial-mesenchymal transition caused by the excess RA was rescued by the addition of Tgfß2 in an organ culture system. These data suggest that RA signaling participates in the Tbx2 transcriptional mechanism during OFT development and that the Tbx2-Tgfß2 cascade is one of the key pathways involved in inducing the TGA phenotype.

Nodal signal is required for morphogenetic movements of epiblast layer in the pre-streak chick blastoderm.

During axis formation in amniotes, posterior and lateral epiblast cells in the area pellucida undergo a counter-rotating movement along the midline to form primitive streak (Polonaise movements). Using chick blastoderms, we investigated the signaling involved in this cellular movement in epithelial-epiblast. In cultured posterior blastoderm explants from stage X to XI embryos, either Lefty1 or Cerberus-S inhibited initial migration of the explants on chamber slides. In vivo analysis showed that inhibition of Nodal signaling by Lefty1 affected the movement of DiI-marked epiblast cells prior to the formation of primitive streak. In Lefty1-treated embryos without a primitive streak, Brachyury expression showed a patchy distribution. However, SU5402 did not affect the movement of DiI-marked epiblast cells. Multi-cellular rosette, which is thought to be involved in epithelial morphogenesis, was found predominantly in the posterior half of the epiblast, and Lefty1 inhibited the formation of rosettes. Three-dimensional reconstruction showed two types of rosette, one with a protruding cell, the other with a ventral hollow. Our results suggest that Nodal signaling may have a pivotal role in the morphogenetic movements of epithelial epiblast including Polonaise movements and formation of multi-cellular rosette.

Heart development before beating.

During heart development at the pregastrula stage, prospective heart cells reside in the posterior lateral region of the epiblast layer. Interaction of tissues between the posterior epiblast and hypoblast is necessary to generate the future heart mesoderm. Signaling regulating the interaction involves fibroblast growth factor (FGF)-8, Nodal, bone morphogenetic protein (BMP)-antagonist, and canonical Wnt and acts on the posterior epiblast to induce the expression of genes specific for the anterior lateral mesoderm. At the early gastrula stage, prospective heart cells accumulate at the posterior midline and migrate to the anterior region of the primitive streak. During gastrulation, future heart cells leave the primitive streak and migrate anterolaterally to form the left and right anterior lateral plate mesoderm including the precardiac mesoderm. At this stage, prospective heart cells receive endoderm-derived signals, including BMP, FGF, and Wnt-antagonist, and thereby become committed to the heart lineage. At the neurula stage, the left and right precardiac mesoderm move to the ventral midline and fuse, resulting in the formation of a single primitive heart tube. Therefore, a two-step signaling cascade, which includes tissue interaction between epiblast and hypoblast at the blastula stage and endoderm-derived signals during gastrulation, is required to generate a beating heart.

ROCK1 expression is regulated by TGFbeta3 and ALK2 during valvuloseptal endocardial cushion formation.

During early heart development at the looped heart stage, endothelial cells in the outflow tract and atrioventricular (AV) regions transform into mesenchyme to generate endocardial cushion tissue. This endocardial epithelial-mesenchymal transition (EMT) is regulated by several regulatory pathways, including the transforming growth factor-beta (TGFbeta), bone morphogenetic protein (BMP), and Rho-ROCK pathways. Here, we investigated the spatiotemporal expression pattern of ROCK1 mRNA during EMT in chick and examined whether TGFbeta or BMP could induce the expression of ROCK1. At the onset of EMT, ROCK1 expression was up-regulated in endothelial/mesenchymal cells. A three-dimensional collagen gel assay was used to examine the mechanisms regulating the expression of ROCK1. In AV endocardium co-cultured with associated myocardium, ROCK1 expression was inhibited by either anti-TGFbeta3 antibody, anti-ALK2 antibody or noggin, but not SB431542 (ALK5 inhibitor). In cultured preactivated AV endocardium, TGFbeta3 protein induced the expression of ROCK1, but BMP did not. AV endothelial cells that were cultured in medium supplemented with TGFbeta3 plus anti-ALK2 antibody failed to express ROCK1. These results suggest that the expression of ROCK1 is up-regulated at the onset of EMT and that signaling mediated by TGFbeta3/ALK2 together with BMP is involved in the expression of ROCK1.

Induction of initial heart alpha-actin, smooth muscle alpha-actin, in chick pregastrula epiblast: the role of hypoblast and fibroblast growth factor-8.

During heart development at the gastrula stage, inhibition of bone morphogenetic protein (BMP) activity affects the heart specification but does not impair the expression of smooth muscle alpha-actin (SMA), which is first expressed in the heart mesoderm and recruited into initial heart myofibrils. Interaction of tissues between posterior epiblast and hypoblast at the early blastula stage is necessary to induce the expression of SMA, in which Nodal and Chordin are thought to be involved. Here we investigated the role of fibroblast growth factor-8 (FGF8) in the expression of SMA. In situ hybridization and reverse transcription-polymerase chain reaction showed that Fgf8b is expressed predominantly in the nascent hypoblast. Anti-FGF8b antibody inhibited the expression of SMA, cTNT, and Tbx5, which are BMP-independent heart mesoderm/early cardiomyocyte genes, but not Brachyury in cultured posterior blastoderm, and combined FGF8b and Nodal, but neither factor alone induced the expression of SMA in association with heart specific markers in cultured epiblast. Although FGF8b did not induce the upregulation of phospho-Smad2, anti-FGF8b properties suppressed phospho-Smad2 in cultured blastoderm. FGF8b was able to reverse the BMP-induced inhibition of cardiomyogenesis. The results suggest that FGF8b acts on the epiblast synergistically with Nodal at the pregastrula stage and may play a role in the expression of SMA during early cardiogenesis.

Erythrophagocytosis by liver macrophages (Kupffer cells) promotes oxidative stress, inflammation, and fibrosis in a rabbit model of steatohepatitis: implications for the pathogenesis of human nonalcoholic steatohepatitis.

Nonalcoholic steatohepatitis (NASH) is a progressive fibrotic disease, the pathogenesis of which has not been fully elucidated. Here, we report a molecular aspect of this disease elucidated using rabbits fed a cholesterol-rich high-fat diet and exhibiting insulin resistance. The liver in this model showed steatohepatitis with fibrosis and high mRNA expression for some cytokines, heme oxygenase-1, transforming growth factor-beta1, and collagen alpha1(I). Erythrocytes isolated from the model showed marked fragility and the externalization of phosphatidylserine (PS) on the outer leaflet of the membrane and were frequently engulfed by Kupffer cells/macrophages in the hepatic sinusoids. Expression of milk fat globule-epidermal growth factor (EGF)-factor 8, a PS-binding protein, was augmented in the liver. In culture, RAW 264.7 cells engulfed erythrocytes oxidized by tert-butyl hydroperoxide, a process that was inhibited by anti-milk fat globule-EGF-factor 8 antibody. In addition, PS-positive erythrocytes appeared entrapped in the model liver in ex vivo perfusion experiments. Finally, in specimens from NASH patients, the aggregation of erythrocytes in inflammatory hepatic sinusoids was notable. These results indicate that the engulfment of PS-externalized, apoptotic signal-positive, erythrocytes by hepatic macrophages may lead to the deposition of iron derived from hemoglobin in the liver and be involved in the pathogenesis of steatohepatitis.

Rho kinase inhibitor Y27632 affects initial heart myofibrillogenesis in cultured chick blastoderm.

During early vertebrate development, Rho-associated kinases (ROCKs) are involved in various developmental processes. Here, we investigated spatiotemporal expression patterns of ROCK1 protein and examined the role of ROCK during initial heart myofibrillogenesis in cultured chick blastoderm. Immunohistochemistry showed that ROCK1 protein was distributed in migrating mesendoderm cells, visceral mesoderm of the pericardial coelom (from which cardiomyocytes will later develop), and cardiomyocytes of the primitive heart tube. Pharmacological inhibition of ROCK by Y27632 did not alter the myocardial specification process in cultured posterior blastoderm. However, Y27632 disturbed the formation of striated heart myofibrils in cultured posterior blastoderm. Furthermore, Y27632 affected the formation of costamere, a vinculin/integrin-based rib-like cell adhesion site. In such cardiomyocytes, cell-cell adhesion was disrupted and N-cadherin was distributed in the perinuclear region. Pharmacological inactivation of myosin light chain kinase, a downstream of ROCK, by ML-9 perturbed the formation of striated myofibrils as well as costameres, but not cell-cell adhesion. These results suggest that ROCK plays a role in the formation of initial heart myofibrillogenesis by means of actin-myosin assembly, and focal adhesion/costamere and cell-cell adhesion.

[Dissection of the heart: a useful guide to understanding the three-dimensional gross anatomy].

In order to understand the three-dimensional gross anatomy of the heart, it is important to observe the inner structures of the chambers and the spatial relation between the valves and the ventricles. In our dissecting laboratory, we designed a guide to dissection of the heart according to the following procedures. First, we observe the surface anatomy of the heart in the pericardial cavity, remove the heart and then identify the coronary vessels, open the four chambers and observe the intra-cardiac structures. Next, we remove the atria from the ventricles and examine the relation between the valves and the chambers. Our guide is useful for learning the three-dimensional gross anatomy which is fundamental to understanding the normal function and disease of the heart.