rerio has emerged as the model of choice for such studies as it
presents many advantages [3]: zebrafish are easily raised in the
laboratory, genetically tractable and produce large cohorts of externally developing embryos, which are optically transparent. Imaging
live zebrafish embryos has allowed the study of dynamic cell behaviour in great detail and highlighted the importance of cell and
tissue interactions.
The study of cell migration is one of the areas that have particularly benefited from live imaging in zebrafish. The germ primordium, lateral line, and immune cells are examples of migratory
model systems that have been studied. Our laboratory has concentrated on the analysis of neural crest cells (NC). NC are an ideal
model to study cell migration as they arise early in development,
being readily accessible to manipulation and imaging. Furthermore, they present a variety of migratory modalities using distinct
substrates for movement. They also share many characteristics with
metastatic cells, including genetic regulatory networks and cellular
behavior [4, 5].
NC arise early in development and migrate extensively invading
most of the embryonic tissues and differentiating into a plethora of
derivatives from neurons and pigment, to chromaffin cells [6]. NC
are induced at the end of gastrulation between the open neural
plate and prospective epidermis. After neural tube closure, NC
reside at its dorsal-most region from where they migrate ventrally
in a rostro-caudal sequence. Cranial NC (CNC) initiate movement
first, forming streams with large numbers of collectively migrating
mesenchymal cells. These groups move superficially between the
epidermis and the neural tissue (Fig. 1). In the trunk, NC start
migrating later in development, colonizing the medial part of each
body segment. Trunk NC (TNC) take two different routes around
the somites: the medial or the lateral pathway [7]. In the medial
pathway, cells wedge between the neural tube and the notochord
covering the medial region of the somite in the anteroposterior axis.
These form unicellular chains of collectively migrating mesenchymal cells. Alternatively, TNC can take the lateral pathway moving
superficially between the somite and the epidermis as single mesenchymal cells.
The study of NC migration requires labelling, imaging, tracking, and quantitative analysis of cell movement at the individual and
collective level within a group; and each step presents specific
challenges. The first is obtaining suitable fluorescent reporter lines
that specifically label NC cells. Several different lines have been
generated using the regulatory elements of the NC genes FoxD3,
Crestin, and Sox10 (Table 1). Most of these lines bear cytoplasmic
or membrane fluorescent proteins, which hinder the identification
and tracking of single cells within tightly packed groups. To circumvent this problem, we have developed the Sox10:mG
kg312Tg
line [8] in which chromatin is marked with red fluorescence
80
Zain Alhashem et al.
presents many advantages [3]: zebrafish are easily raised in the
laboratory, genetically tractable and produce large cohorts of externally developing embryos, which are optically transparent. Imaging
live zebrafish embryos has allowed the study of dynamic cell behaviour in great detail and highlighted the importance of cell and
tissue interactions.
The study of cell migration is one of the areas that have particularly benefited from live imaging in zebrafish. The germ primordium, lateral line, and immune cells are examples of migratory
model systems that have been studied. Our laboratory has concentrated on the analysis of neural crest cells (NC). NC are an ideal
model to study cell migration as they arise early in development,
being readily accessible to manipulation and imaging. Furthermore, they present a variety of migratory modalities using distinct
substrates for movement. They also share many characteristics with
metastatic cells, including genetic regulatory networks and cellular
behavior [4, 5].
NC arise early in development and migrate extensively invading
most of the embryonic tissues and differentiating into a plethora of
derivatives from neurons and pigment, to chromaffin cells [6]. NC
are induced at the end of gastrulation between the open neural
plate and prospective epidermis. After neural tube closure, NC
reside at its dorsal-most region from where they migrate ventrally
in a rostro-caudal sequence. Cranial NC (CNC) initiate movement
first, forming streams with large numbers of collectively migrating
mesenchymal cells. These groups move superficially between the
epidermis and the neural tissue (Fig. 1). In the trunk, NC start
migrating later in development, colonizing the medial part of each
body segment. Trunk NC (TNC) take two different routes around
the somites: the medial or the lateral pathway [7]. In the medial
pathway, cells wedge between the neural tube and the notochord
covering the medial region of the somite in the anteroposterior axis.
These form unicellular chains of collectively migrating mesenchymal cells. Alternatively, TNC can take the lateral pathway moving
superficially between the somite and the epidermis as single mesenchymal cells.
The study of NC migration requires labelling, imaging, tracking, and quantitative analysis of cell movement at the individual and
collective level within a group; and each step presents specific
challenges. The first is obtaining suitable fluorescent reporter lines
that specifically label NC cells. Several different lines have been
generated using the regulatory elements of the NC genes FoxD3,
Crestin, and Sox10 (Table 1). Most of these lines bear cytoplasmic
or membrane fluorescent proteins, which hinder the identification
and tracking of single cells within tightly packed groups. To circumvent this problem, we have developed the Sox10:mG
kg312Tg
line [8] in which chromatin is marked with red fluorescence
80
Zain Alhashem et al.