Molecular analyses of yolk syncytial layer formation and its role in zebrafish embryogenesis

点击翻译按钮获取中文摘要

Fish embryos consist of two major compartments: the blastoderm in the animal pole and yolk in the vegetal pole. The blastoderm consists of cells that make the fish body, while the yolk is a structure that is important for storage of nutrients and signalling molecules. Between these two compartments, there is a thin layer of tissue called the Yolk Syncytial Layer (YSL). The YSL is a single cell layer that has many nuclei (the status of a single cell with multiple nuclei is called a syncytium). The precursors of YSL cells are normal cells that have a single nucleus. However, at 500-1000 cell stage, when the YSL is forming, these cell membranes collapse, cells fuse and become single cells with multiple nuclei. The YSL separates the blastoderm and yolk, and the role of the YSL is to transfer and metabolise nutrients as well as to send signals for the patterning of the embryo. As the signalling centre for patterning, the YSL sends signals to neighbouring blastoderm cells and guides these cells to become mesendoderm (precursor of muscle, kidney, gonad, blood, digestive system and others) and also to obtain regional character (e.g. the YSL guides cells to become head, trunk or tail). Although the YSL does not exist in mammals, equivalent cells with similar activities do, therefore the study of the YSL would be of general interest to all vertebrate researchers including physicians studying human development. Despite the importance of the YSL in embryonic development, the molecular mechanisms under which the YSL is formed have not yet been investigated. From our previous genetic screening, we isolated a gene (we named it yugo-b) that is specifically expressed in the YSL. When we knocked down the gene function of yugo-b and related gene, yugo-a, we found that YSL formation is specifically disrupted. Therefore this would be the first gene that has been identified as a crucial regulator of YSL formation. By using this gene as an experimental tool, we aim to investigate the molecular mechanisms of syncytium formation by cell fusion occurring in the YSL. Since the zebrafish embryo is transparent, and YSL formation occurs at specific times in a synchronised manner, the YSL is an ideal system to study cell fusion events occurring in embryonic development. By utilising many tools available in the zebrafish system (genetics, genome information, gene-knockdown using morphlino antisense oligonucleotides, labelling cell structures with fluorescent proteins, whole mount in situ hybridisation, etc.) we aim to obtain a range of results providing insight into the processes of formation of the YSL and the different components, structures, mechanisms and molecules involved.