Role of autophagy in chondrocyte differentiation

Poster presentation - Theme 3: Development & stem cellsMaintaining cell homeostasis during cellular differentiation is critical for the cell survival. Therefore, the balance between protein biogenesis and degradation is tightly regulated. The removal of the after-used and unwanted substances is not only important for protein turnover but also in regulating cellular differentiation and developmental process. The degradation of protein relies on two well-known systems, the Ubiquitin-proteasome system (UPS) and Autophagy-lysosomal system (ALS). Here, using the unique organization of the growth plate that depicts temporal and spatial “life time” of chondrocytes during ...postprin

The developmental roles of the extracellular matrix: Beyond structure to regulation

Cells in multicellular organisms are surrounded by a complex three-dimensional macromolecular extracellular matrix (ECM). This matrix, traditionally thought to serve a structural function providing support and strength to cells within tissues, is increasingly being recognized as having pleiotropic effects in development and growth. Elucidation of the role that the ECM plays in developmental processes has been significantly advanced by studying the phenotypic and developmental consequences of specific genetic alterations of ECM components in the mouse. These studies have revealed the enormous contribution of the ECM to the regulation of key processes in morphogenesis and organogenesis, such as cell adhesion, proliferation, specification, migration, survival, and differentiation. The ECM interacts with signaling molecules and morphogens thereby modulating their activities. This review considers these advances in our understanding of the function of ECM proteins during development, extending beyond their structural capacity, to embrace their new roles in intercellula signaling. © 2009 Springer-Verlag.postprin

Expression of the mouse α1(II) collagen gene is not restricted to cartilage during development

The mouse alpha 1(II) collagen gene has been isolated and a 5' portion of the gene which has low homology to other collagen genes was used to study the pattern of expression during mouse embryogenesis. In situ hybridization studies show that in the mouse, like the chick, alpha 1(II) collagen is expressed in chondrogenic tissues in advance of chondrocyte differentiation. The gene is expressed early in embryogenesis at 9.5 days both in the cranial mesenchyme destined for the chondrocranium, and the sclerotome of the somites, and at 12.5 days in the primordia of the hyoid and the laryngeal cartilage. Type II collagen gene transcripts were found in all the chondrogenic tissues of the axial and appendicular skeleton until the onset of endochondral ossification. Expression of alpha 1(II) collagen mRNA was also observed in non-chondrogenic tissues such as the notochord which may be responsible for inducing chondrogenesis in somitic mesoderm, neural retina, the corneal and conjunctival epithelia and sclera of the developing eye. Expression in the tail tendon was late, at 16.5-18.5 days. Transient expression was also found in the heart at 9.5-12.5 days, the epidermis at 10.5-14.5 days, the calvarial mesenchyme at 12.5-16.5 days, the inner ear at 14.5 days and the fetal brain from 9.5-14.5 days. Within the neural tube, alpha 1(II) collagen mRNA was localized in the proliferative ventricular cells of the forebrain and midbrain of 9.5- to 10.5-day embryos. Subsequently, transcription of the alpha 1(II) collagen gene was confined to restricted areas of the rhombencephalic basal plate, the ventricular layer of the hindbrain and the cervical spinal cord. These examples of expression of the type II collagen gene in the developing nervous system seem to suggest that active transcription of this gene might be associated with early stages of neuroblast differentiation. Type II collagen may therefore have additional roles in development unrelated to chondrogenesis.published_or_final_versio

Uncoupled endochondral ossification in transgenic mice expressing type X collagen with mutations in the NC1 domain

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Different cis-regulatory DNA elements mediate developmental stage- and tissue-specific expression of the human COL2A1 gene in transgenic mice

Expression of the type II collagen gene (human COL2A1, mouse Col2a1) heralds the differentiation of chondrocytes. It is also expressed in progenitor cells of some nonchondrogenic tissues during embryogenesis. DNA sequences in the 5' flanking region and intron 1 are known to control tissue- specific expression in vitro, but the regulation of COL2A1 expression in vivo is not clearly understood. We have tested the regulatory activity of DNA sequences from COL2A1 on the expression of a lacZ reporter gene in transgenic mice. We have found that type II collagen characteristic expression of the transgene requires the enhancer activity of a 309-bp fragment (+2,388 to +2,696) in intron 1 in conjunction with 6.1-kb 5' sequences. Different regulatory elements were found in the 1.6-kb region (+701 to +2,387) of intron 1 which only needs 90-bp 5' sequences for tissue-specific expression in different components of the developing cartilaginous skeleton. Distinct positive and negative regulatory elements act together to control tissue- specific transgene expression in the developing midbrain neuroepithelium. Positive elements affecting expression in the midbrain were found in the region from -90 to -1,500 and from +701 to +2,387, whereas negatively acting elements were detected in the regions from -1,500 to -6,100 and +2,388 to +2,855.published_or_final_versio

MMP14 regulates the lineage progression of hypertrophic chondrocytes

It is traditionally believed that chondrocytes and osteoblasts are two separate lineages with hypertrophic chondrocytes (HCs) being the terminal stage of chondrocyte differentiation, culminating in apoptosis. However, we have shown that HCs can contribute to the full osteoblast (Obs) lineage in vivo. MMP14 is a transmembrane matrix metalloproteinase responsible for matrix remodeling that is highly expressed at the chondro‐osseous junction which coincides with the transition from HCs to Obs. Knockout of Mmp14 in mice results in impaired endochondral ossification. To test whether loss of MMP14 has an impact on the HC to Obs transition, we have employed a genetic recombination approach to track and compare the fate of HCs in wild‐type and Mmp14 conditional and total null mutants. Both complete and conditional deletion of MMP14 activity results in increased number of HC‐descendent cells in the trabecular bone. Surprisingly, conditional knockout of Mmp14 in HC‐descendent cells results in increased trabecular bone formation. Our results suggest that MMP14 in general negatively regulates HC to Obs transition.postprin

Increased basal insulin secretion in Pdzd2-deficient mice

Expression of the multi-PDZ protein Pdzd2 (PDZ domain-containing protein 2) is enriched in pancreatic islet β cells, but not in exocrine or α cells, suggesting a role for Pdzd2 in the regulation of pancreatic β-cell function. To explore the in vivo function of Pdzd2, Pdzd2-deficient mice were generated. Homozygous Pdzd2 mutant mice were viable and their gross morphology appeared normal. Interestingly, Pdzd2-deficient mice showed enhanced glucose tolerance in intraperitoneal glucose tolerance tests and their plasma insulin levels indicated increased basal insulin secretion after fasting. Moreover, insulin release from mutant pancreatic islets was found to be twofold higher than from normal islets. To verify the functional defect in vitro, Pdzd2 was depleted in INS-1E cells using two siRNA duplexes. Pdzd2-depleted INS-1E cells also displayed increased insulin secretion at low concentrations of glucose. Our results provide the first evidence that Pdzd2 is required for normal regulation of basal insulin secretion. © 2009 Elsevier Ireland Ltd. All rights reserved.postprin

SOXE neofunctionalization and elaboration of the neural crest during chordate evolution

During chordate evolution, two genome-wide duplications facilitated acquisition of vertebrate traits, including emergence of neural crest cells (NCCs), in which neofunctionalization of the duplicated genes are thought to have facilitated development of craniofacial structures and the peripheral nervous system. How these duplicated genes evolve and acquire the ability to specify NC and their derivatives are largely unknown. Vertebrate SoxE paralogues, most notably Sox9/10, are essential for NC induction, delamination and lineage specification. In contrast, the basal chordate, amphioxus, has a single SoxE gene and lacks NC-like cells. Here, we test the hypothesis that duplication and divergence of an ancestral SoxE gene may have facilitated elaboration of NC lineages. By using an in vivo expression assay to compare effects of AmphiSoxE and vertebrate Sox9 on NC development, we demonstrate that all SOXE proteins possess similar DNA binding and homodimerization properties and can induce NCCs. However, AmphiSOXE is less efficient than SOX9 in transactivation activity and in the ability to preferentially promote glial over neuronal fate, a difference that lies within the combined properties of amino terminal and transactivation domains. We propose that acquisition of AmphiSoxE expression in the neural plate border led to NCC emergence while duplication and divergence produced advantageous mutations in vertebrate homologues, promoting elaboration of NC traits.published_or_final_versio

Identification and characterization of long-range SOX9 enhancers in limb development

The transcription factor Sox9 is a master regulator of skeletogenesis. Heterozygous mutations of human SOX9 result in Campomelic Dysplasia (CD), in which affected individuals display distinct abnormalities in limbs and other skeletal assemblies. Recently, chromosomal translocations and deletions at >1Mb from SOX9 have been detected in some CD patients, suggesting the requirement of long‐range regulatory elements in mediating both spatiotemporal and dosage of Sox9 during limb development. To this end, we exploited several published ChIP‐Seq data, and identified nine, evolutionarily conserved, putative limb enhancers of SOX9, namely E1Sox9 to E9Sox9. Transgenic mouse embryos carrying E1Sox9‐driven LacZ reporter showed discrete transgene expression at the pre‐scapular domain where endogenous Sox9 is also expressed. Bioinformatic analyses on our candidate enhancers result in the identification of several signaling effector binding motifs, and indeed, we revealed that BMP‐Smad and Shh‐Gli pathways are possible upstream regulatory networks that govern the spatiotemporal and dosage of limb Sox9 expression via our predicted enhancers, respectively. Our results unveil the underlying molecular control in governing the complex patterning of Sox9 expression in the developing limb, and provide new molecular insight to the etiology of CD syndrome.postprin

Investigating molecular pathogenesis of Campomelic Dysplasia

Student Stage Presentation Session 1: no. T01Two decades after the discovery that sequence alterations within and around SOX9 cause Campomelic Dysplasia (CD) - a rare skeletal malformation syndrome characterized by severe bowing of long bones (campomelia), the underlying molecular pathogenesis leading to bone dysmorphism remains unclear ...postprin