Project description:Here, we show lists of 10 up- and 87 down-regulated genes obtained by a cDNA microarray analysis that compared developing Myf5-/-:Myod-/- (and Mrf4-/-) petrous part of the temporal bone, containing middle and inner ear, to the control, at embryonic day 18.5. Myf5-/-:Myod-/- fetuses entirely lack skeletal myoblasts and muscles. They are unable to move their head, which interferes with the perception of angular acceleration. Previously, we showed that the inner ear areas most affected in Myf5-/- :Myod-/- fetuses were the vestibular cristae ampullaris, sensitive to angular acceleration. Our finding that the type I hair cells were absent in the mutants’ cristae was further used here to identify a profile of genes specific to the lacking cell type. Microarrays followed by a detailed consultation of web-accessible mouse databases allowed us to identify 6 candidate genes with a possible role in the development of the inner ear sensory organs: Actc1, Pgam2, Ldb3, Eno3, Hspb7 and Smpx. Additionally, we searched for human homologues of the candidate genes since a number of syndromes in humans have associated inner ear abnormalities. Mutations in one of our candidate genes, Smpx, have been reported as the cause of X-linked deafness in humans. Our current study suggests an epigenetic role that mechanical, and potentially other, stimuli originating from muscle, play in organogenesis, and offers an approach to finding novel genes responsible for altered inner ear phenotypes.
Project description:Skeletal (striated) muscle is one of the four basic tissue types, together with the epithelium, connective and nervous tissues. Lungs, on the other hand, develop from the foregut and among various cell types contain smooth, but not skeletal muscle. Therefore, during earlier stages of development, it is unlikely that skeletal muscle and lung depend on each other. However, during the later stages of development, respiratory muscle, primarily the diaphragm and the intercostal muscles, execute so called fetal breathing-like movements (FBMs), that are essential for lung growth and cell differentiation. In fact, the absence of FBMs results in pulmonary hypoplasia, the most common cause of death in the first week of human neonatal life. Most knowledge on this topic arises from in vivo experiments on larger animals and from various in vitro experiments. In the current era of mouse mutagenesis and functional genomics, it was our goal to develop a mouse model for pulmonary hypoplasia. We employed various genetically engineered mice lacking different groups of respiratory muscles or lacking all the skeletal muscle and established the criteria for pulmonary hypoplasia in mice, and therefore established a mouse model for this disease. We followed up this discovery with systematic subtractive microarray analysis approach and revealed novel functions in lung development and disease for several molecules. We believe that our approach combines elements of both in vivo and in vitro approaches and allows us to study the function of a series of molecules in the context of lung development and disease and, simultaneously, in the context of lung's dependence on skeletal muscle-executed FBMs.
Project description:Previous analysis of Myf5-/-:MyoD-/- mouse fetuses lacking skeletal muscle demonstrated the importance of muscle contraction and static loading in mouse skeletogenesis. Previous analysis of Myf5-/-:MyoD-/- mouse fetuses lacking skeletal muscle demonstrated the importance of muscle contraction and static loading in mouse skeletogenesis. Among abnormal skeletal features, micrognathia (mandibular hypoplasia) was detected: small, bent and posteriorly displaced mandible. As an example of Waddingtonian epigenetics, we suggest that muscle, in addition to acting via mechanochemical signal transduction pathways, networks and promoters, also exerts secretory stimuli on skeleton. Our goal is to identify candidate molecules at that muscle-mandible interface. By employing Systematic Subtractive Microarray Analysis approach, we compared gene expression between mandibles of amyogenic and wild type mouse fetuses. We identified a set of candidate genes with involvement in mandibulardevelopment: Cacna1s, Ckm, Des, Mir300, Myog and Tnnc1. We also performed mouse-to-human translational experiments and found analogies. In the light of our findings we discuss various players in mandibular morphogenesis and make an argument for the need to consider mandibular development as a consequence of reciprocal epigenetic interactions of both skeletal and non-skeletal compartments.
Project description:The involvement of skeletal muscle in the process of palatal development in mammals is an example of Waddingtonian epigenetics. Our earlier study showed that the cleft palate develops in the complete absence of skeletal musculature during embryonic development in mice. This contrasts with previous beliefs that tongue obstruction prevents the elevation and fusion of the palatal shelves. We argue that the complete absence of mechanical stimuli from the adjacent muscle, i.e., the lack of both static and dynamic loading, results in disordered palatogenesis. We further suggest that proper fusion of the palatal shelves depends not only on mechanical but also on paracrine contributions from the muscle. The muscle's paracrine role in the process of palatal fusion is achieved through its being a source of certain secreted and/or circulatory proteins. A cDNA microarray analysis revealed differentially expressed genes in the cleft palate of amyogenic mouse fetuses and suggested candidate molecules with a novel function in palatogenesis (e.g., Tgfbr2, Bmp7, Trim71, E2f5, Ddx5, Gfap, Sema3f). In particular, we report on Gdf11 mutant mouse that has cleft palate, and on several genes whose distribution is normally restricted to the muscle (completely absent in our amyogenic mouse model), but which are found down-regulated in amyogenic mouse cleft palate. These molecules probably present a subset of paracrine cues that influence palatogenesis from the adjacent muscle. Future studies will elucidate the role of these genes in muscle-palate crosstalk, connecting the cues produced by the muscle with the cartilage and bone tissue's responses to these cues, through various degrees of cell proliferation, death, differentiation and tissue fusion.
Project description:Myocardin-related transcription factors (MRTFs) play a central role in the regulation of actin expression and cytoskeletal dynamics. Stimuli that promote actin polymerization allow for shuttling of MRTFs to the nucleus where they activate serum response factor (SRF), a regulator of actin and other cytoskeletal protein genes. SRF is an essential regulator of skeletal muscle differentiation and numerous components of the muscle sarcomere, but the potential involvement of MRTFs in skeletal muscle development has not been examined. We explored the role of MRTFs in muscle development in vivo by generating mutant mice harboring a skeletal muscle-specific deletion of MRTF-B and a global deletion of MRTF-A. These double knockout (dKO) mice were able to form sarcomeres during embryogenesis. However, the sarcomeres were abnormally small and disorganized, causing skeletal muscle hypoplasia and perinatal lethality. Transcriptome analysis demonstrated dramatic dysregulation of actin genes in MRTF dKO mice, highlighting the importance of MRTFs in actin cycling and myofibrillogenesis. MRTFs were also necessary for the survival of skeletal myoblasts and for the efficient formation of intact myotubes. Our findings reveal a central role for MRTFs in sarcomere formation during skeletal muscle development and point to the potential involvement of these transcriptional coactivators in skeletal myopathies. Gene expression profile was generated comparing wild type (WT) and HSA-Cre, MRTF-A/B double knockout mice, by deep seqencing, with three biological replicates, using Illumina HiSeq 2500.
Project description:Myocardin-related transcription factors (MRTFs) play a central role in the regulation of actin expression and cytoskeletal dynamics. Stimuli that promote actin polymerization allow for shuttling of MRTFs to the nucleus where they activate serum response factor (SRF), a regulator of actin and other cytoskeletal protein genes. SRF is an essential regulator of skeletal muscle differentiation and numerous components of the muscle sarcomere, but the potential involvement of MRTFs in skeletal muscle development has not been examined. We explored the role of MRTFs in muscle development in vivo by generating mutant mice harboring a skeletal muscle-specific deletion of MRTF-B and a global deletion of MRTF-A. These double knockout (dKO) mice were able to form sarcomeres during embryogenesis. However, the sarcomeres were abnormally small and disorganized, causing skeletal muscle hypoplasia and perinatal lethality. Transcriptome analysis demonstrated dramatic dysregulation of actin genes in MRTF dKO mice, highlighting the importance of MRTFs in actin cycling and myofibrillogenesis. MRTFs were also necessary for the survival of skeletal myoblasts and for the efficient formation of intact myotubes. Our findings reveal a central role for MRTFs in sarcomere formation during skeletal muscle development and point to the potential involvement of these transcriptional coactivators in skeletal myopathies.