Seminarios

Hox Control of Drosophila Feeding Behaviour
Dr. Ingrid Lohmann
BIOQUANT-Zentrum, University of Heidelberg

Summary: Food uptake is a crucial behaviour of all animals, which depends on the rhythmic activity of feeding-associated muscles triggered by brain motoneurons. Despite its vital importance, critical determinants instructing the development, wiring and connectivity of neuromuscular feeding networks are largely unknown. Here we identify the Hox transcription factor Deformed (Dfd) to be expressed and functional in specific motoneurons and muscles, which are essential for food ingestion in Drosophila. Using genetic, molecular, genomic and behavioural approaches we demonstrate that Dfd is required at subsequent phases of motor network formation by directly controlling neuronal specification, axon outgrowth, synapse formation and neurotransmission. The synchronous regulation of cell adhesion molecules in feeding-associated motoneurons and muscles furthermore uncovers Dfd as a decisive factor of synaptic target recognition. Finally, we demonstrate that the Dfd homolog Hoxb4 is expressed in neurons projecting towards head muscles in the vertebrate model medaka, indicating a general and conserved role of homology group 4 Hox genes in neuromuscular network formation.

How cell know how big they are
Prof. Fred Chang
Columbia University, NY

Transcription and R-loops in genome instability
Dr. Andrés Aguillera
Universidad de Sevilla-CABIMER

Summary: Genome instability is a cell pathology characterized by high levels of mutation, recombination or chromosome loss that is commonly associated with cancer and a number of genetic diseases. One key cellular process compromising genome integrity is transcription, which can contribute to genome instability via the formation of R-loops or by collisions with the replication machinery. Deciphering the factors and mechanisms responsible for transcription-associated instability is essential to understand genome dynamics and the molecular basis by which different gene expression steps, from transcription to RNA processing and export, can threaten genome integrity.

Reflections on the Future
Dr. Peter Rigby
The Institute of Cancer Research, London; Deputy Chairman to the Wellcome Trust.

Summary: I have been asked to think about the future of our field. When I first became interested in developmental biology, almost exactly thirty years ago, there were three big questions. The first was what is the molecular basis of Lewis Wolpert’s French Flag, which roughly translates as “what is a morphogen”? The second was how are the body axes determined? And the third was how do you make a specialised cell from an uncommitted progenitor? Do we have satisfactory answers to those questions? Yes but it all depends on who you are and how much granularity you want. I think that most biologists are of the view that we know enough. On the other hand, I could easily make you a long list of things that I still want to know about how you make a skeletal muscle, which has been my obsession for twenty years. There may well be technological advances that will take the field to a new level. Ever improving microscopes, ways of getting cells to talk to us, improved proteomics,and ways of imaging molecular interactions in real time in vivo. But if we want to continue to explore fundamental developmental problems, we have to persuade both our scientific colleagues and our political masters to give us money, and that, with the notable exception of the brain,may not be easy. We will have to find ways of justifying what we want to do other than simply saying “it is interesting and important”. Applied developmental biology, stem cell biology and regenerative medicine, will be fine. But if we want to continue to do pure developmental biology we will have to focus on issues which have general applicability and are thus of interestto the wider community of biologists. I do not wish to be gloomy because I think that there is much we can do but we will ignore the issues at our peril.

Kinase crosstalk: mitotic kinases as anti-cancer targets
Dr. Mar Carmena
University of Edinburgh

Summary: Cell division is regulated by highly conserved families of mitotic kinases, among them Polo-like and Aurora kinases. Our research focuses in the study of how these kinases interact and coordinate their activities to ensure accurate cell cycle progression. In recent years the use of anti-mitotic agents in anticancer chemotherapy has proven a highly successful approach. The quest is now on to find new anti-mitotic drugs equally efficient but with less undesirable side effects. Aurora and Polo kinases have been identified as targets for the development of new anti mitotic drugs. I will describe our new screens for anti-mitotic agents using both human cells and Drosophila as model systems.

Dr Katherine Brown
Development, COB

Enhancing hexosamine pathway flux improves C. elegans protein homeostasis and extends life
Dr. Adam Antebi
Max Planck Institute for Biology of Ageing, Cologne

Summary: Organismal ageing entails the progressive loss of cellular homeostasis - including protein homeostasis, which comprises all processes maintaining a functional proteome. The endoplasmic reticulum (ER) is an important site of protein synthesis and quality control, and a particularly vulnerable point in disease. To identify mutants with improved ER quality control we isolated mutants resistant to tunicamycin, a drug which interferes with ER protein folding by inhibiting N-glycosylation. We identified gain-of-function mutations in glucosamine-fructose 6-phosphate aminotransferase (gfat-1), which is the rate limiting enzyme in the hexosamine pathway producing UDP-GlcNac for O- and N-linked glycosylation. Notably, such mutants are long-lived and improve the management of proteotoxic species. Mutants have elevated levels of UDP-GlcNac, and feeding this metabolite to wild type animals is sufficient to extend life span and ameliorate various proteinopathies. These studies reveal that endogenous metabolites can enhance health and extend life through protein quality control mechanisms.

Multiple functions of Fibroblast Growth Factor signaling in Drosophila gastrulation
Dr. Arno Muller
College of Life Sciences, Univ. of Dundee

Summary: The Muller laboratory is interested in cell signaling networks that control epithelial mesenchymal morphogenesis using Drosophila melanogaster as a model. During gastrulation of the fly embryo, and in fact many other organisms, mesoderm cells are derived from epithelial precursors and undergo a transition to mesenchymal cells, which collectively move to form a cell layer that becomes separated from the other germ layers. We used genetic screens to identify genes involved in mesoderm layer formation and identified components of an FGF signaling pathway to be central players in this process. Our studies show that FGF signaling operates at several distinct steps during mesoderm morphogenesis including epithelial mesenchymal transition, cell attachment, directional migration and cell differentiation. The screens also revealed molecular players in the FGF signaling pathway elucidating how the FGF receptor translates the extracellular signal into changes in cell behavior. The seminar will summarise the cellular roles of FGF signaling in mesoderm layer formation and discuss requirements of small GTPases of the Rho family and amino-sugar nucleotide metabolism for this morphogenetic event.

Heart Development and Regeneration
Dr. Eldad Tzahor
Weizmann Institute of Science. Department of Biological Regulation

Summary: Over the past few years we have focused on the developmental programs of the heart and skeletal muscles of the head. In contrast to our understanding of how skeletal muscle is formed in the trunk, much less is known about the tissues and molecules that induce the formation of the head musculature. Our studies over the last decade have addressed the origins, signaling, and genetics of distinct head muscles. Considerable cellular and genetic variations exist among the different craniofacial muscle groups, and their associated satellite cells. Cellular and molecular parallels are drawn between cardiac and pharyngeal muscle developmental programs, and argue for the tissues’ common evolutionary origins. During embryogenesis, parts of the heart and craniofacial muscles arise from common origins within the pharyngeal mesoderm (PM). I will present unpublished data revealing a hierarchical gene regulatory network of transcription factors expressed in PM progenitors that initiates heart and craniofacial organogenesis. Genetic ablation experiments that perturbed this network in mice resulted in severe heart and craniofacial muscle defects. We identified Lhx2, a LIM domain transcription factor, as a novel player during cardiac and pharyngeal muscle development. Lhx2 and the bHLH transcription factor Tcf21 genetically interact with Tbx1; furthermore knockout of these genes recapitulates specific features of DiGeorge/velo-cardio-facial/22q11.2 deletion syndrome. We suggest that PM-derived cardiogenesis and myogenesis are network properties, rather than properties specific to individual PM members. These findings shed new light on the developmental underpinnings of congenital heart and craniofacial defects.

From Networks to Pattern Formation - Computational Models of Development
Dr. Dagmar Iber
ETHZ, Zurich

Summary: Mouse organogenesis has been studied for decades. While much is known about the genes that affect organ formation, general regulatory paradigms are largely lacking to explain the emergence of functional organization in biology. A number of mathematical theories have been proposed to explain biological pattern formation, but these have rarely been tested experimentally. With the emergence of the field of systems biology the two approaches are becoming increasingly interlinked and experimentally validated computational models of mouse organogenesis that integrate the detailed experimental knowledge are being generated. I will present our recent models of branching morphogenesis and limb development. Our data-based models not only help to detect inconsistencies in experimental data, but also allow to define the underlying regulatory mechanisms and to distinguish core and accessory regulatory interactions. These models also present a useful tool for in silico genetics, i.e. the computational simulations of the expected phenotypes of mutant states that are difficult or impossible to generate by mouse molecular genetics.

Role of skeletal muscle in the epigenetic shaping of organs and cell fate choices
Prof. Boris Kablar
Dalhousie University School of Medicine, Halifax, Canada

Summary: In this presentation, I will review a few concepts in Developmental Biology, according to which, cells, tissues and organs are each other’s environment. Various cues from that environment, such as molecular (e.g., paracrine), mechanical and other cues, are thought to influence embryonic development in a reciprocal (mutual) way, creating complex networking systems that connect the genotype and the phenotype. In the first part, I will explain how lung development depends on mechanical stimuli from the respiratory musculature. I will introduce novel players in the mechanochemical signal transduction pathway that operate to connect the mechanical stimuli and the alveolar epithelial cell differentiation. The human disease that is modeled in this example is Pulmonary Hypoplasia. In the second part, I will explain the developmental relationship between skeletal muscle, motor neurons and giant pyramidal cells in the spinal cord and brain, respectively. I will introduce novel molecular players in the process of motor neuron number regulation. The human disease that is modeled in this example is Amyotrophic Lateral Sclerosis (ALS) or Lou Gehrig's Disease. In the last part, I will explain developmental relationships between skeletal muscle and the skeleton. In particular, I will concentrate on the events of fusion and secondary cartilage development. I will introduce novel molecular players involved in skeletal development, and examine new concepts explaining the human disease that is modeled here, known as Palatoschisis or Cleft Palate.

Sequence-based discovery of human and Drosophila regulons
Dr Stein Aerts
Laboratory of Computational Biology Center for Human Genetics University of Leuven

Summary: The identification and characterization of functional cis-regulatory elements in eukaryotic genomes remains a key challenge in genome biology. We present a computational framework to analyse a human, mouse, or fly gene network or gene signature and to confidently identify cis-regulatory modules and transcription factor (TF) binding sites. The framework uses Hidden Markov Models to identify motif clusters, combined with comparative genomics cues, rank statistics to identify enriched motifs, and a “motif2TF” step to prioritize candidate transcription factors (TF) for each enriched motif. The Drosophila version of our method (called i-cisTarget) utilizes large collections of motifs (>6000 position weight matrices) and of 'regulatory tracks' (> 500 data sets) as cues, including the entire modEncode and BDTNP data sets. The human version of our method (called iRegulon) works as a Cytoscape plugin and thereby integrates cis-regulatory sequence analysis with network biology. To illustrate our methods, we show two case studies, one in Drosophila retinal determination and the second in human cancer. For the Drosophila case study we have performed cross-species transcriptomics by next-generation sequencing across three Drosophila species and obtained a highly conserved core set of eye-specific genes. Motif and CRM discovery unveiled a regulatory network downstream of the transcription factor Glass, which we validated by RNA-Seq in glass mutant eyes and by in vivo enhancer-reporter assays. For the human case study we have performed RNA-Seq and ChIP-Seq analysis for TP53 in a breast cancer cell line and show how iRegulon successfully identifies known and novel TP53 binding sites and target genes. Encouraged by these results, we applied iRegulon to more than twenty thousand cancer gene signatures obtained both from signature databases and from bi-clustering 91 large cancer gene expression datasets, and defined for each TF a context-free “meta-targetome”. In conclusion, i-cisTarget and iRegulon are next-generation motif discovery methods that confidently identify master regulators and bona fide direct targets from sets of co-regulated genes.