The role of microRNAs miR206 and miR133 in somite development and myogenesis

Multi-cellular organisms contain many distinct cell types with very specialized functions. For example, we need skeletal muscle to be able to move while our skin prevents dehydration and protects us from injury and infections. Amazingly all these different cells arise from a single cell, the fertilized egg. The development of an embryo begins when the egg starts dividing to give rise to many cells. Different cells are specified during embryonic development. This means that they are essentially told what to do and what to become by molecular signals that act in the early embryo. These signals often cause specific genes to be switched 'on' or 'off'. If a gene is 'on' it is expressed which means that it is actively transcribed from the DNA in the nucleus of the cell. During the process of transcription, DNA is copied into RNA. These RNA transcripts typically encode proteins and RNA is translated into proteins by a complex cellular machinery. Proteins are the 'movers and shakers' in a cell and they have specific jobs to do. For example, they control the processes of transcription and translation and therefore help to make more proteins. Proteins are also an important part of the building blocks of a cell, for example, the contractile fibres of a muscle cells or the rigid cytoskeleton of a skin cell. However, not all RNA is translated to make protein and the RNA molecule itself can have important functions. A new class of these non-coding RNAs was discovered recently. Because this class of RNAs is very small, they were called microRNAs. They have been found in plants and animals, which means, that they are most likely part of the most basic machinery of life with a very important and fundamental job to do in all cells. This turned out to be the case and in fact microRNAs control whether or not other coding RNAs are translated into protein. A lot of research is being done, to help understand how this is happening and to uncover what type of cellular processes are controlled in this fashion. Our research investigates how cells become different from one another in a developing vertebrate embryo. In particular, we study the genes and molecules that control the decision of a cell to differentiate into skeletal muscle from a multi-potent precursor, as opposed to into bone for example. We recently discovered that two of these new microRNAs (and there are currently more than 200 microRNAs known) are only present in those cells in the embryo, that will go on to make skeletal muscle and we want to understand what the role of these microRNAs is. This includes to figure out how the production of the microRNA itself is being switched 'on' or 'off', and to identify which other genes are controlled by the microRNAs. Overall we will learn how an embryo makes normal, healthy, working muscle and this will in the long-term benefit patients who suffering from various muscle degenerative diseases.

We are interested in the molecular signalling networks controlling early events in vertebrate embryogenesis. We investigate a number of different processes which impact upon these including pattern formation and cell specification as well as cell movement. We want to understand how multi-potent embryonic progenitor cells are instructed to differentiate into distinct cell types at the correct time and in the right place. We use the developing somite in chick embryos, which will give rise to a number of distinct mesodermal cell lineages including skeletal muscle, as a model to investigate this question. This project will investigate the importance of two novel microRNAs for the specification and differentiation of cells within the developing somite. Preliminary work has demonstrated that miR206 is specifically expressed in the myotome, the part of the somite that contains skeletal muscle progenitor cells. We have also begun to investigate the role of signalling pathways known to be involved in somite patterning and differentiation for the regulation of miR206 gene expression. Our experiments have uncovered a role for FGF mediated signalling in the initiation of miR206 expression and this will be further investigated using established methods, such as the implantation of beads soaked in recombinant FGF proteins or pharmacological inhibitors. We will characterize targets for both miR206 and miR133 and use cell culture based approaches to validate them experimentally. Lastly, we will clone novel microRNAs and further characterize those that are involved in somite differentiation. The precise roles for microRNAs in embryonic development are not completely understood and nothing is known about how their expression is regulated by develomental signaling pathways. This work will make a significant contribution to our understanding of microRNA function during myogenesis and yield more general insights into the fundamental mechanisms employed in vertebrate embryogenesis.