Expression and regulation of the Msx1 natural antisense transcript during development

Bidirectional transcription, leading to the expression of an antisense (AS) RNA partially complementary to the protein coding sense (S) RNA, is an emerging subject in mammals and has been associated with various processes such as RNA interference, imprinting and transcription inhibition. Homeobox genes do not escape this bidirectional transcription, raising the possibility that such AS transcription occurs during embryonic development and may be involved in the complexity of regulation of homeobox gene expression. According to the importance of the Msx1 homeobox gene function in craniofacial development, especially in tooth development, the expression and regulation of its recently identified AS transcripts were investigated in vivo in mouse from E9.5 embryo to newborn, and compared with the S transcript and the encoded protein expression pattern and regulation. The spatial and temporal expression patterns of S, AS transcripts and protein are consistent with a role of AS RNA in the regulation of Msx1 expression in timely controlled developmental sites. Epithelial–mesenchymal interactions were shown to control the spatial organization of S and also AS RNA expression during early patterning of incisors and molars in the odontogenic mesenchyme. To conclude, this study clearly identifies the Msx1 AS RNA involvement during tooth development and evidences a new degree of complexity in craniofacial developmental biology: the implication of endogenous AS RNAs

Severe Compromise of Preosteoblasts in a Surgical Mouse Model of Bisphosphonate-Associated Osteonecrosis of the Jaw.

Objectives: The effect of amino-bisphosphonates on osteoblastic lineage and its potential contribution to the pathogenesis of bisphosphonate-associated osteonecrosis of the jaw (BONJ) remain controversial. We assessed the effects of zoledronic acid (ZOL) on bone and vascular cells of the alveolar socket using a mouse model of BONJ. Material and Methods: Thirty-two mice were treated twice a week with either 100 μg/kg of ZOL or saline for 12 weeks. The first left maxillary molar was extracted at the third week. Alveolar sockets were assessed at both 3 weeks (intermediate) and 9 weeks (long-term) after molar extraction by semi-quantitative histomorphometry for empty lacunae, preosteoblasts (Osterix), osteoclasts (TRAP), and pericyte-like cells (CD146). Also, the bone microarchitecture was assessed by micro-CT. Results: Osteonecrotic-like lesions were observed in 21% of mice. Moreover, a decreased number of preosteoblasts contrasted with the increased number of osteoclasts at both time points. In addition, osteoclasts display multinucleation and detachment from the endosteal surface. Furthermore, the number of pericyte-like cells increased at the intermediate time point. The alveolar bone mass increased exclusively with long-term ZOL treatment. Conclusion: The severe imbalance between bone-forming cells and bone-resorbing cells showed in this study could contribute to the pathogenesis of BONJ

The contribution of immune infiltrates and the local microenvironment in the pathogenesis of osteosarcoma

International audienceOsteosarcoma is a rare primary bone cancer characterized by cancer cells producing calcified osteoid extracellular matrix and inducing lung metastases with a high frequency. The local microenvironment defined several tumor niches controlling the tumor growth and cell extravasation. The immune infiltrate composes one of these niches. The immune environment of osteosarcoma is mainly composed by T-lymphocytes and macrophages but also contains other subpopulations including B-lymphocytes and mast cells. Osteosarcoma cells control the recruitment and differentiation of immune infiltrating cells and establish a local immune tolerant environment favorable to the tumor growth, drug resistance and the occurrence of metastases. Osteosarcoma cells are able to affect the balance between M1 and M2 macrophage subtypes and so could control the T-lymphocyte responses via the PD-1/PDL-1 system. In addition, mesenchymal stem cells may also contribute to this immune tolerance and strengthen the immune evasion. The present review gives a brief overview of the immune components of osteosarcoma and their most recent therapeutic interests

Effets de l’inhibition post-natale de RANKL sur l’éruption et la formation radiculaire des molaires de souris C57BL/6

Introduction : Des observations récentes effectuées dans le service d’ODF de la Pitié-Salpêtrière à Paris montrent une augmentation des altérations de l’éruption des molaires permanentes non-familiales. Nos travaux récents au laboratoire montrent l’implication des ostéoclastes (OC) dans les processus d’éruption et de rétention dentaires avec implication de la voie de signalisation RANKL/RANK/OPG. Ces faits nous ont amenés à émettre l’hypothèse d’une étiologie environnementale à l’origine de ces défauts d’éruption qui correspondrait à la perturbation des voies de signalisation cellulaires autocrines/paracrines telles que la voie RANKL/RANK/OPG. Matériels et méthodes : Des souris C57BL/6 ont subi des injections d’anticorps anti- RANKL à intervalles réguliers au cours des neuf premiers jours après la naissance. Une comparaison phénotypique avec les souris transgéniques RANK a permis la caractérisation fonctionnelle de la voie RANK/RANKL. Le complexe dento-alvéolaire a été analysé par micro-CT pour la densité osseuse, et la coloration au trichrome de Masson pour les examens histologiques. Résultats : L’invalidation transitoire de RANKL a conduit à un arrêt du développement radiculaire des molaires et l’inhibition de l’éruption dentaire contrairement au phénotype des souris surexprimant RANK. Le recrutement et l’activité des ostéoclastes ont été fortement altérés. Discussion : Ces recherches présentent un intérêt clinique tant direct concernant la compréhension des pathologies de l’éruption qu’indirect pour l’établissement des protocoles de traitements orthodontiques pour les cas particuliers

Enamel Protein Regulation and Dental and Periodontal Physiopathology in Msx2 Mutant Mice

Signaling pathways that underlie postnatal dental and periodontal physiopathology are less studied than those of early tooth development. Members of the muscle segment homeobox gene (Msx) family encode homeoproteins that show functional redundancy during development and are known to be involved in epithelial-mesenchymal interactions that lead to crown morphogenesis and ameloblast cell differentiation. This study analyzed the MSX2 protein during mouse postnatal growth as well as in the adult. The analysis focused on enamel and periodontal defects and enamel proteins in Msx2-null mutant mice. In the epithelial lifecycle, the levels of MSX2 expression and enamel protein secretion were inversely related. Msx2+/− mice showed increased amelogenin expression, enamel thickness, and rod size. Msx2−/− mice displayed compound phenotypic characteristics of enamel defects, related to both enamel-specific gene mutations (amelogenin and enamelin) in isolated amelogenesis imperfecta, and cell-cell junction elements (laminin 5 and cytokeratin 5) in other syndromes. These effects were also related to ameloblast disappearance, which differed between incisors and molars. In Msx2−/− roots, Malassez cells formed giant islands that overexpressed amelogenin and ameloblastin that grew over months. Aberrant expression of enamel proteins is proposed to underlie the regional osteopetrosis and hyperproduction of cellular cementum. These enamel and periodontal phenotypes of Msx2 mutants constitute the first case report of structural and signaling defects associated with enamel protein overexpression in a postnatal context