Molecular mechanisms of cell migration and pattern formation

Lead Research Organisation: MRC National Inst for Medical Research

Abstract

A central aspect of the development of multicellular organisms is the formation of the appropriate cell type forms in the right places, a process called pattern formation. This process involves cell-cell interactions and regulated cell migration. We study the zebrafish posterior lateral line that consists of primary mechano-receptive organs regularly spaced along the trunk. These organs are derived from a migrating group of cells or primordium, that is formed posterior to the developing ear, and during migration deposits a clump of cells from the trailing end at regular intervals. How is this precise pattern generated, what initiated the migration and makes the primordium to move in a particular direction, how does it know where to deposit small clump of cells and what kind of molecules involved in these processes? ||Cell-cell communication is vital in controlling cell behaviour and organising patterns. Regulation of cytoskeleton and cell adhesions underlies cell migration. To address the above questions we first like to learn more about the cell behaviours during the migration, deposition of cells in the developing posterior lateral line. We are investigating the roles of several molecules known to be active in the developing lateral line, particularly those involved in cell-cell communication and regulating cytoskeleton and cell adhesions. We set out to identify novel molecules and study their functions in pattern formation and cell migration. Combined with molecular analyses, grafting experiments are being carried out to uncover the signal(s) setting up the polarity and direction of migration of the primordium.

Technical Summary

The lateral line is a specialised sensory system of fishes and aquatic amphibians that arises from an ectodermal placode located adjacent to the developing ear. The lateral line placode differentiates to form the ganglion and a primordium that migrates along a precise route. During migration, clusters of cells are deposited at specific locations and they subsequently form the first, or primary, neuromasts. The differentiated neuromasts are composed of clusters of mechanosensory hair cells surrounded by two types of nonsensory support cells. Thus, the development of the lateral line involves a variety of important cellular events, such as the formation and differentiation of a placode, determination of tissue polarity, cell migration and guidance, pattern formation and differentiation of clusters of cells.||The aim of our work is to identify and understand the roles of molecules underlying directional cell migration using the developing lateral line as a model system. This involves four lines of investigation that use image analysis, gene cloning and functional studies, embryological manipulations and genetic screens.||The first line of work is to carry out time-lapse imaging to learn about the normal cell behaviours during the differentiation of the placode, migration and deposition of the primordium. The superficial location of the developing lateral line placode and migrating primordium and the transparency of the zebrafish embryos are ideal for observing cell behaviour in living embryos. This will provide insights into the cell shape changes, cell movements and interactions within the primordium and with the environment. We have obtained molecular and morphological evidence that the formation of neuromasts is prepatterned by formation of clusters of cells within the migrating posterior lateral line primordium. We are now focusing our effort in defining the initial stages of migration. This line of work will be extended to visualise molecular activities regulating cytoskeletal and adhesion dynamics during cell migration. To this end we have established a lateral line specific Gal4 driver line using BAC recombination technology. Currently we are carrying out detailed characterisation of the line and establishing several UAS lines to visualise cytoskeleton and adhesion dynamics.||The second approach is to identify mutants in which patterning of the lateral line is altered. The number and spacing of the primary posterior lateral line neuromasts are stereotyped and can serve as distinct phenotypic markers. We have developed a simple screening procedure for changes in the number, appearance and distribution of the neuromasts. A pilot F3 screen of 50 families failed to identify any mutations affecting the lateral line development. We are focusing our screen on TILLING mutants affecting specific genes. ||The third line of work is directed towards identifying molecules involved in the formation of lateral line system, and to understand their functions. We are interested in elucidating functions of several regulatory genes, e.g., hmx2 and 3, expressed in the developing lateral line by loss and gain of function analyses. We are also working on guidance molecules to define their roles in directed migration.||The fourth line of work is to combine embryological graft experiments with analyses of molecular markers to address questions regarding tissue polarity and the direction of cell migration.||Current Entry in Implications for improving health or health care and/or increasing wealth: Several genes are involved in cell migration during development and tumour progression and elucidating molecular mechanisms underlying cell migration in development will help to understand the migration of tumour cells in metastasis.||Current Entry in Key Words: Vertebrate embryo development, pattern formation, cell migration, cell adhesion, chemoattraction, cytoskeletal dynamics, cell behaviour, tissue polarity, image analysis, molecular biology.

Publications

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