To roll the eyes and snap a bite - function, development and evolution of craniofacial muscles.

Craniofacial muscles, muscles that move the eyes, control facial expression and allow food uptake and speech, have long been regarded as a variation on the general body muscle scheme. However, evidence has accumulated that the function of head muscles, their developmental anatomy and the underlying regulatory cascades are distinct. This article reviews the key aspects of craniofacial muscle and muscle stem cell formation and discusses how this differs from the trunk programme of myogenesis; we show novel RNAseq data to support this notion. We also trace the origin of head muscle in the chordate ancestors of vertebrates and discuss links with smooth-type muscle in the primitive chordate pharynx. We look out as to how the special properties of head muscle precursor and stem cells, in particular their competence to contribute to the heart, could be exploited in regenerative medicine.

Requirement of Pitx2 for skeletal muscle homeostasis.

Skeletal muscle is generated by the successive incorporation of primary (embryonic), secondary (fetal), and tertiary (adult) fibers into muscle. Conditional excision of Pitx2 function by an MCKCre driver resulted in animals with histological and ultrastructural defects in P30 muscles and fibers, respectively. Mutant muscle showed severe reduction in mitochondria and FoxO3-mediated mitophagy. Both oxidative and glycolytic energy metabolism were reduced. Conditional excision was limited to fetal muscle fibers after the G1-G0 transition and resulted in altered MHC, Rac1, MEF2a, and alpha-tubulin expression within these fibers. The onset of excision, monitored by a nuclear reporter gene, was observed as early as E16. Muscle at this stage was already severely malformed, but appeared to recover by P30 by the expansion of adjoining larger fibers. Our studies demonstrate that the homeodomain transcription factor Pitx2 has a postmitotic role in maintaining skeletal muscle integrity and energy homeostasis in fetal muscle fibers.

Differential gene regulatory networks in development and disease.

Gene regulatory networks, in which differential expression of regulator genes induce differential expression of their target genes, underlie diverse biological processes such as embryonic development, organ formation and disease pathogenesis. An archetypical systems biology approach to mapping these networks involves the combined application of (1) high-throughput sequencing-based transcriptome profiling (RNA-seq) of biopsies under diverse network perturbations and (2) network inference based on gene-gene expression correlation analysis. The comparative analysis of such correlation networks across cell types or states, differential correlation network analysis, can identify specific molecular signatures and functional modules that underlie the state transition or have context-specific function. Here, we review the basic concepts of network biology and correlation network inference, and the prevailing methods for differential analysis of correlation networks. We discuss applications of gene expression network analysis in the context of embryonic development, cancer, and congenital diseases.

Chemokine signaling in cancer-stroma communications.

Cancer is a multi-faceted disease in which spontaneous mutation(s) in a cell leads to the growth and development of a malignant new organ that if left undisturbed will grow in size and lead to eventual death of the organism. During this process, multiple cell types are continuously releasing signaling molecules into the microenvironment, which results in a tangled web of communication that both attracts new cell types into and reshapes the tumor microenvironment as a whole. One prominent class of molecules, chemokines, bind to specific receptors and trigger directional, chemotactic movement in the receiving cell. Chemokines and their receptors have been demonstrated to be expressed by almost all cell types in the tumor microenvironment, including epithelial, immune, mesenchymal, endothelial, and other stromal cells. This results in chemokines playing multifaceted roles in facilitating context-dependent intercellular communications. Recent research has started to shed light on these ligands and receptors in a cancer-specific context, including cell-type specificity and drug targetability. In this review, we summarize the latest research with regards to chemokines in facilitating communication between different cell types in the tumor microenvironment.

Expanding the Natural Products Heterologous Expression Repertoire in the Model Cyanobacterium Anabaena sp. Strain PCC 7120: Production of Pendolmycin and Teleocidin B-4.

Cyanobacteria are prolific producers of natural products, and genome mining has shown that many orphan biosynthetic gene clusters can be found in sequenced cyanobacterial genomes. New tools and methodologies are required to investigate these biosynthetic gene clusters, and here we present the use of Anabaena sp. strain PCC 7120 as a host for combinatorial biosynthesis of natural products using the indolactam natural products (lyngbyatoxin A, pendolmycin, and teleocidin B-4) as a test case. We were able to successfully produce all three compounds using codon optimized genes from Actinobacteria. We also introduce a new plasmid backbone based on the native Anabaena 7120 plasmid pCC7120ζ and show that production of teleocidin B-4 can be accomplished using a two-plasmid system, which can be introduced by coconjugation.

FACS-Seq analysis of Pax3-derived cells identifies non-myogenic lineages in the embryonic forelimb.

Skeletal muscle in the forelimb develops during embryonic and fetal development and perinatally. While much is known regarding the molecules involved in forelimb myogenesis, little is known about the specific mechanisms and interactions. Migrating skeletal muscle precursor cells express Pax3 as they migrate into the forelimb from the dermomyotome. To compare gene expression profiles of the same cell population over time, we isolated lineage-traced Pax3+ cells (Pax3 EGFP ) from forelimbs at different embryonic days. We performed whole transcriptome profiling via RNA-Seq of Pax3+ cells to construct gene networks involved in different stages of embryonic and fetal development. With this, we identified genes involved in the skeletal, muscular, vascular, nervous and immune systems. Expression of genes related to the immune, skeletal and vascular systems showed prominent increases over time, suggesting a non-skeletal myogenic context of Pax3-derived cells. Using co-expression analysis, we observed an immune-related gene subnetwork active during fetal myogenesis, further implying that Pax3-derived cells are not a strictly myogenic lineage, and are involved in patterning and three-dimensional formation of the forelimb through multiple systems.

Mapping the Chromatin State Dynamics in Myoblasts.

BACKGROUND: Genome-wide mapping reveals chromatin landscapes unique to cell states. Histone marks of regulatory genes involved in cell specification and organ development provide a powerful tool to map regulatory sequences. H3K4me3 marks promoter regions; H3K27me3 marks repressed regions, and Pol II presence indicates active transcription. The presence of both H3K4me3 and H3K27me3 characterize poised sequences, a common characteristic of genes involved in pattern formation during organogenesis. RESULTS: We used genome-wide profiling for H3K27me3, H3K4me3, and Pol II to map chromatin states in mouse embryonic day 12 forelimbs in wild type (control) and Pitx2-null mutant mice. We compared these data with previous gene expression studies from forelimb Lbx1+ migratory myoblasts and correlated Pitx2-dependent expression profiles and chromatin states. During forelimb development, several lineages including myoblast, osteoblast, neurons, angioblasts etc., require synchronized growth to form a functional limb. We identified 125 genes in the developing forelimb that are Pitx2-dependent. Genes involved in muscle specification and cytoskeleton architecture were positively regulated, while genes involved in axonal path finding were poised. CONCLUSION: Our results have established histone modification profiles as a useful tool for identifying gene regulatory states in muscle development, and identified the role of Pitx2 in extending the time of myoblast progression, promoting formation of sarcomeric structures, and suppressing attachment of neuronal axons.

Phenotypic Screening of Drug Library in Actively Differentiating Mouse Embryonic Stem Cells.

Phenotypic screening enables the discovery of new drug leads with novel targets. ES cells differentiate into different lineages by successively making use of different subsets of the genome's possible macromolecular interactions. If a compound effectively targets just one of these interactions, it derails the developmental pathway to produce a phenotypical change. The OTRADI microsource spectrum library of 2000 approved drug components, natural products, and bioactive components was screened for compounds that can induce phenotypic changes in ES cell cultures at 10 µM after 3 days. Twenty-one compounds that induced specific morphologies also induced unique changes to an expression profile of a dozen markers of early embryonic development, indicating that each compound has derailed the molecular developmental process in a characteristic way. Phenotypic screens conducted with ES cultures differentiating along different lineages can be used to efficiently prescreen compounds able to regulate cell differentiation lineage.

Assessment of Anabaena sp. Strain PCC 7120 as a Heterologous Expression Host for Cyanobacterial Natural Products: Production of Lyngbyatoxin A.

Cyanobacteria are well-known producers of natural products of highly varied structure and biological properties. However, the long doubling times, difficulty in establishing genetic methods for marine cyanobacteria, and low compound titers have hindered research into the biosynthesis of their secondary metabolites. While a few attempts to heterologously express cyanobacterial natural products have occurred, the results have been of varied success. Here, we report the first steps in developing the model freshwater cyanobacterium Anabaena sp. strain PCC 7120 (Anabaena 7120) as a general heterologous expression host for cyanobacterial secondary metabolites. We show that Anabaena 7120 can heterologously synthesize lyngbyatoxin A in yields comparable to those of the native producer, Moorea producens, and detail the design and use of replicative plasmids for compound production. We also demonstrate that Anabaena 7120 recognizes promoters from various biosynthetic gene clusters from both free-living and obligate symbiotic marine cyanobacteria. Through simple genetic manipulations, the titer of lyngbyatoxin A can be improved up to 13-fold. The development of Anabaena 7120 as a general heterologous expression host enables investigation of interesting cyanobacterial biosynthetic reactions and genetic engineering of their biosynthetic pathways.