Ectodermal Research Articles

Epigenomic reprogramming in peripheral nerve injury.

Epigenomic reprogramming in peripheral nerve injury.

The apical ectodermal ridge of the mouse model of ectrodactyly Dlx5;Dlx6-/- shows altered stratification and cell polarity, which are restored by exogenous Wnt5a ligand.

The congenital malformation split hand/foot (SHFM) is characterized by missing central fingers and dysmorphology or fusion of the remaining ones. Type-1 SHFM is linked to deletions/rearrangements of the DLX5–DLX6 locus and point mutations in the DLX5 gene. The ectrodactyly phenotype is reproduced in mice by the double knockout (DKO) of Dlx5 and Dlx6. During limb development, the apical ectodermal ridge (AER) is a key-signaling center responsible for early proximal–distal growth and patterning. In Dlx5;6 DKO hindlimbs, the central wedge of the AER loses multilayered organization and shows down-regulation of FGF8 and Dlx2. In search for the mechanism, we examined the non-canonical Wnt signaling, considering that Dwnt-5 is a target of distalless in Drosophila and the knockout of Wnt5, Ryk, Ror2 and Vangl2 in the mouse causes severe limb malformations. We found that in Dlx5;6 DKO limbs, the AER expresses lower levels of Wnt5a, shows scattered β-catenin responsive cells and altered basolateral and planar cell polarity (PCP). The addition of Wnt5a to cultured embryonic limbs restored the expression of AER markers and its stratification. Conversely, the inhibition of the PCP molecule c-jun N-terminal kinase caused a loss of AER marker expression. In vitro, the addition of Wnt5a on mixed primary cultures of embryonic ectoderm and mesenchyme was able to confer re-polarization. We conclude that the Dlx-related ectrodactyly defect is associated with the loss of basoapical and PCP, due to reduced Wnt5a expression and that the restoration of the Wnt5a level is sufficient to partially reverts AER misorganization and dysmorphology.

Spatiotemporal Expression of p63 in Mouse Epidermal Commitment.

The embryonic surface ectoderm is a simple flat epithelium consisting of cells that express the cytokeratins K8/K18. Before stratification, K5/K14 expression substitutes K8/K18 expression, marking the event called epidermal commitment. Previous studies show that the transcription factor p63 plays an essential role in epidermal commitment. However, detailed expression information of p63 during early epidermal development in mice is still unclear. We systematically studied the expression pattern of p63 in mouse epidermal commitment, together with K8 and K5. We show that p63 expression could be detected as early as E8.5 in mouse embryos preceding epidermal commitment. p63 expression first appears near the newly formed somites and the posterior part of the embryo, further expanding to the whole embryonic surface with particular enrichment in the first branchial arches and the limb buds. ΔNp63 is the major class of isoforms expressed in this period. Relative expression intensity of p63 depends on the embryonic position. In summary, there is a sequential and regular expression pattern of K8, p63 and K5 in mouse epidermal commitment. Our study not only contributes to understanding the early events during epidermal development but also provides a basal tool to study the function of p63 in mammals.

Genome-wide redistribution of H3K27me3 is linked to genotoxic stress and defective growth

H3K9 methylation directs heterochromatin formation by recruiting multiple heterochromatin protein 1 (HP1)-containing complexes that deacetylate histones and methylate cytosine bases in DNA. In Neurospora crassa, a single H3K9 methyltransferase complex, called the DIM-5,-7,-9, CUL4, DDB1 Complex (DCDC), is required for normal growth and development. DCDC-deficient mutants are hypersensitive to the genotoxic agent methyl methanesulfonate (MMS), but the molecular basis of genotoxic stress is unclear. We found that both the MMS sensitivity and growth phenotypes of DCDC-deficient strains are suppressed by mutation of embryonic ectoderm development or Su-(var)3-9; E(z); Trithorax (set)-7, encoding components of the H3K27 methyltransferase Polycomb repressive complex-2 (PRC2). Trimethylated histone H3K27 (H3K27me3) undergoes genome-wide redistribution to constitutive heterochromatin in DCDC- or HP1-deficient mutants, and introduction of an H3K27 missense mutation is sufficient to rescue phenotypes of DCDC-deficient strains. Accumulation of H3K27me3 in heterochromatin does not compensate for silencing; rather, strains deficient for both DCDC and PRC2 exhibit synthetic sensitivity to the topoisomerase I inhibitor Camptothecin and accumulate γH2A at heterochromatin. Together, these data suggest that PRC2 modulates the response to genotoxic stress.

Molecular diagnosis of X-linked hypohidrotic ectodermal dysplasia families

Objective To explore the mutations of EDA gene in 2 X-linked hypohidrotic ectodermal dysplasia(XLHED) pedigrees, and provide clues for the XLHED diagnosis, genetic counseling and treatment. Methods Polymerase chain reaction and direct sequencing were used to analyze the coding sequences and their flanking sequences of the EDA gene in the patients, suspicious carriers, normal family members in 2 families and non-relative control samples. Results In family 1, mutation c. 659_676del18, namely p. 220_225del(Gly-X-Y)6 which was located in(Gly-X-Y)19 collagen-like repeat domain, was found in the proband and other patient's EDA gene.In family 2, an insertion c. 118-119insT was found in the intracellular domain, which induces reading frame alteration from the 40th amino acid.The mutations found in the 2 families were consistent with the principle of mutation and phenotype co-separation, but these mutations were not found in the normal control samples.EDA gene analysis of fetal amniotic fluid sample from Ⅲ-1 in the family 1 was not found to have the same mutation as the proband, and the follow-up after birth proved normal for the baby. Conclusions EDA gene c. 118-119insT mutation found in the research is a novel mutation.Sequence analysis of EDA gene is an efficient method in XLHED diagnosis, and is beneficial for the genetic counseling and the genetic intervention of the disease in the affected families. Key words: Hypohidrotic ectodermal dysplasia; EDA gene; Molecular diagnosis

Congenital Brain and Spinal Cord Malformations and Their Associated Cutaneous Markers

The brain, spinal cord, and skin are all derived from the embryonic ectoderm; this common derivation leads to a high association between central nervous system dysraphic malformations and abnormalities of the overlying skin. A myelomeningocele is an obvious open malformation, the identification of which is not usually difficult. However, the relationship between congenital spinal cord malformations and other cutaneous malformations, such as dimples, vascular anomalies (including infantile hemangiomata and other vascular malformations), congenital pigmented nevi or other hamartomata, or midline hairy patches may be less obvious but no less important. Pediatricians should be aware of these associations, recognize the cutaneous markers associated with congenital central nervous system malformations, and refer children with such markers to the appropriate specialist in a timely fashion for further evaluation and treatment.

Lateral adhesion drives reintegration of misplaced cells into epithelial monolayers.

Cells in simple epithelia orient their mitotic spindles in the plane of the epithelium so that both daughter cells are born within the epithelial sheet. This is assumed to be important to maintain epithelial integrity and prevent hyperplasia, because misaligned divisions give rise to cells outside the epithelium1,2. Here we test this assumption in three types of Drosophila epithelia; the cuboidal follicle epithelium, the columnar early embryonic ectoderm, and the pseudostratified neuroepithelium. Ectopic expression of Inscuteable in these tissues reorients mitotic spindles, resulting in one daughter cell being born outside of the epithelial layer. Live imaging reveals that these misplaced cells reintegrate into the tissue. Reducing the levels of the lateral homophilic adhesion molecules Neuroglian or Fasciclin 2 disrupts reintegration, giving rise to extra-epithelial cells, whereas disruption of adherens junctions has no effect. Thus, the reinsertion of misplaced cells appears to be driven by lateral adhesion, which pulls cells born outside the epithelia layer back into it. Our findings reveal a robust mechanism that protects epithelia against the consequences of misoriented divisions.

Immunohistochemical Study of Expression of Sohlh1 and Sohlh2 in Normal Adult Human Tissues.

The expression pattern of Sohlh1 (spermatogenesis and oogenesis specific basic helix-loop-helix 1) and Sohlh2 in mice has been reported in previous studies. Sohlh1 and Sohlh2 are specifically expressed in spermatogonia, prespermatogonia in male mice and oocytes of primordial and primary follicles in female mice. In this report, we studied the expression pattern of Sohlh1 and Sohlh2 in human adult tissues. Immunohistochemical staining of Sohlh1 and Sohlh2 was performed in 5 samples of normal ovaries and testes, respectively. The results revealed that Sohlh genes are not only expressed in oocytes and spermatogonia, but also in granular cells, theca cells, Sertoli cells and Leydig cells, and in smooth muscles of blood vessel walls. To further investigate the expression of Sohlh genes in other adult human tissues, we collected representative normal adult tissues developed from three embryonic germ layers. Compared with the expression in mice, Sohlhs exhibited a much more extensive expression pattern in human tissues. Sohlhs were detected in testis, ovary and epithelia developed from embryonic endoderm, ectoderm and tissues developed from embryonic mesoderm. Sohlh signals were found in spermatogonia, Sertoli cells and also Leydig cells in testis, while in ovary, the expression was mainly in oocytes of primordial and primary follicles, granular cells and theca cells of secondary follicles. Compared with Sohlh2, the expression of Sohlh1 was stronger and more extensive. Our study explored the expression of Sohlh genes in human tissues and might provide insights for functional studies of Sohlh genes.

Abstract 116: Targeting EZH2 catalytic independent functions in breast cancer

Abstract Advances in drug discovery have enabled the development of catalytic inhibitors or inhibitors that disrupt protein-protein interactions. One validated drug target is the polycomb repressive complex 2 (PRC2), which promotes cancer development and reduces patient survival in multiple cancers. The core of PRC2 consists of Enhancer of Zeste Homolog 2 (EZH2) and Embryonic Ectoderm Development (EED). Currently, inhibitors targeting the catalytic site of EZH2 were efficacious in inhibiting a subset of blood cancers. In addition, a recently developed peptidomimetic inhibitor that disrupts the EED-EZH2 interaction also inhibits PRC2 activity and decreases proliferation of solid tumors. In this study, we investigated the effects of EZH2 protein depletion versus EZH2 catalytic inhibition with two small molecule inhibitors, GSK126 (an EZH2 catalytic inhibitor) and DZNep (a histone methylation inhibitor that depletes EZH2). We found that catalytic inhibition of EZH2 was insufficient to block cancer cell proliferation whereas depletion of EZH2 was effective at killing cancer cells. This study suggests that depleting EZH2 to inhibit both catalytic dependent and independent functions could be useful in the treatment of solid tumors such as breast cancer. Citation Format: Keng Gat Lim. Targeting EZH2 catalytic independent functions in breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 116. doi:10.1158/1538-7445.AM2015-116

Eccrine sweat gland development and sweat secretion.

Eccrine sweat glands help to maintain homoeostasis, primarily by stabilizing body temperature. Derived from embryonic ectoderm, millions of eccrine glands are distributed across human skin and secrete litres of sweat per day. Their easy accessibility has facilitated the start of analyses of their development and function. Mouse genetic models find sweat gland development regulated sequentially by Wnt, Eda and Shh pathways, although precise subpathways and additional regulators require further elucidation. Mature glands have two secretory cell types, clear and dark cells, whose comparative development and functional interactions remain largely unknown. Clear cells have long been known as the major secretory cells, but recent studies suggest that dark cells are also indispensable for sweat secretion. Dark cell-specific Foxa1 expression was shown to regulate a Ca(2+) -dependent Best2 anion channel that is the candidate driver for the required ion currents. Overall, it was shown that cholinergic impulses trigger sweat secretion in mature glands through second messengers - for example InsP3 and Ca(2+) - and downstream ion channels/transporters in the framework of a Na(+) -K(+) -Cl(-) cotransporter model. Notably, the microenvironment surrounding secretory cells, including acid-base balance, was implicated to be important for proper sweat secretion, which requires further clarification. Furthermore, multiple ion channels have been shown to be expressed in clear and dark cells, but the degree to which various ion channels function redundantly or indispensably also remains to be determined.

A new understanding of Pax6, a master regulator in eye and brain development

Background Paired box gene 6 (Pax6) is a master regulator for eye and brain development. Pax6 mutations or changes in its expression cause a series of ocular diseases including absence of iris, corneal opacity, cataract, glaucoma, abnormal fovea, retinoblastoma, and Wilm's tumor-aniridia-qenital ahormalies-retardation (WAGR). As a transcription factor, it is expressed in the region of anterior surface ectoderm corresponding to the future adenohypophyseal, olfactory and lens placodes, optic vesicle and other parts of the future brain and thus control the development of eye, brain, pituitary grand, nose and pancreas. Pax6 exists in 4 different isoforms, whose functions are subjected to regulation by different post-translation modifications. A complete understanding of the structure and functions of Pax6 and its associations with relevant diseases is helpful for ophthalmologists to investigate the pathogenesis and treatment of implicated ocular diseases caused by Pax6 gene mutation or changing in its expression. Key words: Paired box gene 6; Transcription factor; Humans; Eye abnormalities-causing gene; Mutation; Regulation of gene expression; Brain development; Eye development

Inactivation of Eed impedes MLL-AF9–mediated leukemogenesis through Cdkn2a-dependent and Cdkn2a-independent mechanisms in a murine model

Polycomb repressive complex 2 (PRC2) is a chromatin regulator with central roles in development and cancer. The canonical function of PRC2 is the trimethylation of histone 3 on lysine residue 27. This epigenetic modification is associated with gene silencing. Both tumor suppressor and oncogenic functions have been reported for PRC2, depending on cellular context. In leukemia mediated by the leukemogenic fusion MLL-AF9, complete ablation of canonical PRC2 function by genetic inactivation of the core component embryonic ectoderm development (Eed) or by combined pharmacologic inhibition of the PRC2 methyltransferases EZH2 and EZH1 has a strong anti-leukemic effect, and this effect has been linked to de-repression of the PRC2 target locus Cdkn2a. We asked whether inactivation of Cdkn2a is sufficient to restore leukemic activity of Eed-inactivated MLL-AF9 leukemia cells, using combined genetic inactivation of Cdkn2a and Eed. We found that Cdkn2a inactivation partially rescues in vitro and in vivo growth of Eed-inactivated MLL-AF9 cells. However, the growth of Eed-null Cdkn2a-null MLL-AF9 cells in the absence of Cdkn2a remained severely compromised in vitro and in vivo, compared with that of their Eed-floxed Cdkn2a-null counterparts. RNA sequencing analysis revealed that several genes previously implicated in inefficient growth of MLL-AF9-transformed cells, including Gata2, Egr1, and Cdkn2b were de-repressed as a consequence of Eed inactivation. Furthermore, we found that direct binding targets of MLL fusion proteins are negatively enriched in Eed-inactivated Cdkn2a-null MLL-AF9-transformed cells. Our data indicate that interference with PRC2 function affects MLL-AF9-mediated leukemogenesis by both Cdkn2a-dependent and Cdkn2a-independent mechanisms.

Morphological and Gene Expression Changes in Cattle Embryos from Hatched Blastocyst to Early Gastrulation Stages after Transfer of In Vitro Produced Embryos.

A detailed morphological staging system for cattle embryos at stages following blastocyst hatching and preceding gastrulation is presented here together with spatiotemporal mapping of gene expression for BMP4, BRACHYURY, CERBERUS1 (CER1), CRIPTO, EOMESODERMIN, FURIN and NODAL. Five stages are defined based on distinct developmental events. The first of these is the differentiation of the visceral hypoblast underlying the epiblast, from the parietal hypoblast underlying the mural trophoblast. The second concerns the formation of an asymmetrically positioned, morphologically recognisable region within the visceral hypoblast that is marked by the presence of CER1 and absence of BMP4 expression. We have termed this the anterior visceral hypoblast or AVH. Intra-epiblast cavity formation and the disappearance of the polar trophoblast overlying the epiblast (Rauber’s layer) have been mapped in relation to AVH formation. The third chronological event involves the transition of the epiblast into the embryonic ectoderm with concomitant onset of posterior NODAL, EOMES and BRACHYURY expression. Lastly, gastrulation commences as the posterior medial embryonic ectoderm layer thickens to form the primitive streak and cells ingress between the embryonic ectoderm and hypoblast. At this stage a novel domain of CER1 expression is seen whereas the AVH disappears. Comparison with the mouse reveals that while gene expression patterns at the onset of gastrulation are well conserved, asymmetry establishment, which relies on extraembryonic tissues such as the hypoblast and trophoblast, has diverged in terms of both gene expression and morphology.

Masticatory performance and assessment of life quality of children with ectodermal dysplasia after prosthetic rehabilitation

To evaluate masticatory performance and life quality of children with ectodermal dysplasia (ED) after prosthetic rehabilitation. Six children with ED received denture restoration and 18 healthy children were involved in this study. The surface electromyography (EMG) of masseter (MM) and anterior temporalis (TA) during clenching and chewing movement were recorded. The EMG amplitude, area, asymmetry index of total and activity index of MM/TA were compared at each stage. The masticatory efficiency was measured with spectrophotometer. The life quality was assessed using visual analogue scale questionnaire. The EMG amplitude of MM and TA during chewing in ED Group were 41.7% and 45.6% of the control group respectively, the area were 35.9% and 36.0% respectively. Significant difference in asymmetry index of total during clenching was observed between the two groups (P < 0.05) but not during chewing (P > 0.05). The differences of activity index of MM/TA during clenching and chewing between the two groups were not detected (P > 0.05). The masticatory efficiency of ED group was 67.2% of the control group. The score of chewing function in children with ED after prosthetic rehabilitation was three times higher than before, and no difference was present between the two groups (P > 0.05). Early prosthetic rehabilitation can significantly improve the masticatory performance and life quality of children with ED.

Transmission and Scanning Electron Microscopy of the Accessory Cells and Chorion During Development of Ciona intestinalis Type B Embryos and the Impact of Their Removal on Cell Morphology.

Spawned ascidian oocytes are surrounded by a membrane called the chorion (or vitelline coat) and associated with two populations of maternally-supplied cells. Outside the chorion are follicle cells, which may affect the buoyancy of eggs. Inside the chorion are test cells, which during oogenesis provision the egg and which after fertilisation contribute to the larval tunic. The structure of maternal cells may vary between species. The model ascidian Ciona intestinalis has been recently split into two species, currently named type A and type B. The ultrastructure of extraembryonic cells and structures from type A embryos has been reported. Here we describe the ultrastructure of follicle and test cells from C. intestinalis type B embryos. Test cells are about 5 µm in diameter and line the inside of the chorion of developing embryos in a dense sheet. Follicle cells are large (> 100 µm long) and spike-shaped, with many large vesicles. Terminal electron dense granules are found towards the tips of spikes, adjacent to cytoplasm containing numerous small electron dense bodies connected by filaments. These are probably vesicles containing material for the terminal granules. Removal of maternal structures and cells just after fertilisation, as commonly used in many experiments manipulating C. intestinalis development, has been reported to affect embryonic patterning. We examined the impact of this on embryonic ectoderm cells by scanning electron microscopy. Cells of embryos that developed without maternal structures still developed cilia, but had indistinct cell boundaries and a more flattened appearance than those that developed within the chorion.

P113 – 2575: Ectodermal dysplasia presented as fever of unknown origin

Objective To report a case of ectodermal dysplasia that presented as a fever of unknown origin. Ectodermal dysplasia is an inherited disorder that defined by primary defects in development of tissues derived from embryonal ectoderm. The tissues primarily involved are the skin and its appendages (hair follicles, eccrine glands, sebaceous glands, and, nails) and teeth but also can affects ears. Methods A 16 months old boy presented to our clinic with a chief complain of fever started since 10 months earlier. He was referred from a district hospital and had been evaluated for a tuberculosis infection with negative result of tuberculin test. The child noted to have fever 38.0–39.0 degree Celsius, no sign of chronic cough or malnutrition. Chest x-ray showed a suggestive tuberculosis infection and after the first consultation he was sent home for tuberculosis treatment (isoniazid, rifampicin, and pyrazinamide). After two weeks of treatment, there is no improvement of fever. A long and detailed anamnesis was performed and we found out that the parents complains that the patient is never had tears or sweats. The patient also had a motor and speech delay. Brain evoked response audiometry (BERA) showed a bilateral severe hearing loss. Results A diagnosis of hypohydrosis ectodermal dysplasia was made and after a thermoregulation with air conditioner at home, the fever is gone. The patient use hearing aid and started physiotherapy and speech therapy. Artificial tears also prescribed to prevent cornea damage. The parents was refused a skin biopsy. Conclusion Ectodermal dysplasia is a rare disorder that can have different symptoms depends on the tissues affected and vary from mild to severe symptoms. Early recognition of this condition may lead to an early intervention and better prognosis.

Wedelolactone disrupts the interaction of EZH2-EED complex and inhibits PRC2-dependent cancer.

Polycomb repressive complex 2 (PRC2), which is responsible for the trimethylation of H3K27 (H3K27me3), plays a part in tumorigenesis, development and/or maintenance of adult tissue specificity. The pivotal role of PRC2 in cancer makes it a therapeutic target for epigenetic cancer therapy. However, natural compounds targeting the enhancer of zeste homolog 2 (EZH2) - embryonic ectoderm development (EED) interaction to disable PRC2 complex are scarcely reported. Here, we reported the screening and identification of natural compounds which could disrupt the EZH2-EED interaction. One of these compounds, wedelolactone, binds to EED with a high affinity (KD = 2.82 μM), blocks the EZH2-EED interaction in vitro, induces the degradation of PRC2 core components and modulates the expression of detected PRC2 downstream targets and cancer-related genes. Furthermore, some PRC2-dependent cancer cells undergone growth arrest upon treatment with wedelolactone. Thus, wedelolactone and its derivatives which target the EZH2-EED interaction could be candidates for the treatment of PRC2-dependent cancer.

Wnt ligands from the embryonic surface ectoderm regulate 'bimetallic strip' optic cup morphogenesis in mouse.

The Wnt/β-catenin response pathway is central to many developmental processes. Here, we assessed the role of Wnt signaling in early eye development using the mouse as a model system. We showed that the surface ectoderm region that includes the lens placode expressed 12 out of 19 possible Wnt ligands. When these activities were suppressed by conditional deletion of wntless (Le-cre; Wlsfl/fl) there were dramatic consequences that included a saucer-shaped optic cup, ventral coloboma, and a deficiency of periocular mesenchyme. This phenotype shared features with that produced when the Wnt/β-catenin pathway co-receptor Lrp6 is mutated or when retinoic acid (RA) signaling in the eye is compromised. Consistent with this, microarray and cell fate marker analysis identified a series of expression changes in genes known to be regulated by RA or by the Wnt/β-catenin pathway. Using pathway reporters, we showed that Wnt ligands from the surface ectoderm directly or indirectly elicit a Wnt/β-catenin response in retinal pigment epithelium (RPE) progenitors near the optic cup rim. In Le-cre; Wlsfl/fl mice, the numbers of RPE cells are reduced and this can explain, using the principle of the bimetallic strip, the curvature of the optic cup. These data thus establish a novel hypothesis to explain how differential cell numbers in a bilayered epithelium can lead to shape change.

Selective inhibition of EZH2 and EZH1 enzymatic activity by a small molecule suppresses MLL-rearranged leukemia

AbstractEnhancer of zeste homolog 2 (EZH2) and related EZH1 control gene expression and promote tumorigenesis via methylating histone H3 at lysine 27 (H3K27). These methyltransferases are ideal therapeutic targets due to their frequent hyperactive mutations and overexpression found in cancer, including hematopoietic malignancies. Here, we characterized a set of small molecules that allow pharmacologic manipulation of EZH2 and EZH1, which include UNC1999, a selective inhibitor of both enzymes, and UNC2400, an inactive analog compound useful for assessment of off-target effect. UNC1999 suppresses global H3K27 trimethylation/dimethylation (H3K27me3/2) and inhibits growth of mixed lineage leukemia (MLL)–rearranged leukemia cells. UNC1999-induced transcriptome alterations overlap those following knockdown of embryonic ectoderm development, a common cofactor of EZH2 and EZH1, demonstrating UNC1999's on-target inhibition. Mechanistically, UNC1999 preferentially affects distal regulatory elements such as enhancers, leading to derepression of polycomb targets including Cdkn2a. Gene derepression correlates with a decrease in H3K27me3 and concurrent gain in H3K27 acetylation. UNC2400 does not induce such effects. Oral administration of UNC1999 prolongs survival of a well-defined murine leukemia model bearing MLL-AF9. Collectively, our study provides the detailed profiling for a set of chemicals to manipulate EZH2 and EZH1 and establishes specific enzymatic inhibition of polycomb repressive complex 2 (PRC2)–EZH2 and PRC2-EZH1 by small-molecule compounds as a novel therapeutics for MLL-rearranged leukemia.

From osteoblast to osteoclast: new insights of Yin-Yang theory in bone remodeling

Yin-Yang theory plays critical role in traditional Chinese medicine (TCM) science. However, there are many competing interpretations of Yin- Yang theory in the context with the development in biology, and no consensus has been established. Here we first propose that osteoblast should be regarded as Yin, while osteoclast should be considered as Yang in bone remodeling compartment (BRC). Our conceptions are consistent with the following key findings: 1)osteoblast and osteoclast both derive from the embryonic ectoderm; 2)osteoblast and osteoclast work collaboratively in BRC to maintain bone homeostasis; 3)the activities of osteoblast and osteoclast are coupled to remain dynamic balance; 4)osteoblast and osteoclast exert their function in ceaseless successions. Moreover, we argue that Yin-Yang relationships exist between osteoblast and osteoclast: osteoblast secretes the receptor activator for nuclear factor-κB ligand (RANKL) and the monocyte/macrophage colony-stimulating factor (M-CSF) and osteoprotegerin (OPG) to positively or negatively regulate osteoclast differentiation and function. Meanwile, osteoclast and bone resorption in turn release cytokines, such as transforming growth factor-β (TGF-β), insulin-like growth factor-1 (IGF-1) from bone matrix, to regulate osteoblast differentiation and function. Next, the unlimited division of Yin-Yang can be applied to divide sublevel of Yin-Yang inside osteoblast or osteoclast. Finally, Yin-Yang relationship of osteoblast and osteoclast is relative. Therefore, we come into the conclusion that the relationships between osteoblast and osteoclast as established in contemporary biology reflect the classic Yin-Yang in bone remodeling. The new Yin-Yang concepts of osteoblast and osteoclast may strengthen basic theory and clinical practice in TCM.