Lab
Robert Ho Lab
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Statement of Research Interest
Embryonic development of the zebrafish, Danio rerio.
The embryo of the zebrafish is an excellent preparation in which to study many aspects of development. Cells of zebrafish are relatively large, optically clear, and accessible at all stages of development to experimental manipulations such as the microinjection of lineage tracer molecules, cell ablations, and cell transplantations. The zebrafish embryo also has a strong background of genetic analyses, and several interesting mutations have been isolated. In addition, many molecular techniques are becoming increasingly routine in the zebrafish system.
Because zebrafish embryos are optically transparent, it is easy to label individual cells with fluorescent lineage tracers
and follow their development using low light level video time-lapse techniques. By using these methods, Kimmel and his coworkers were able to construct a "fate map" for the zebrafish at gastrulation. A fate map, which is a puzzling together of the various cell lineages of an organism, allows one to accurately predict the identity of the progeny cells produced by a given precursor cell, and therefore is a useful reference model for normal development.
We are interested in understanding how and when individual cells of the early embryo become "committed," that is, irreversibly restricted to expressing a particular cellular identity. The elucidation of the zebrafish fate map has allowed us to perform precise and reproducible
experimental manipulations for the purpose of disturbing the normal cellular processes in defined ways. By studying the effects of these
manipulations on development, we hope to gain insights into the manner by which cellular identity is specified and maintained.
For instance, we now have techniques to transplant individual embryonic cells from one fate map region of a labeled donor embryo to a different region within an unlabeled host. The purpose of these manipulations is to see if the transplanted cell would later express a fate appropriate for its new position (in which case it was still pluripotent and uncomitted to any particular fate), or if it would retain the fate of its original position even though moved to a new location (in which case it could be characterized as committed to its original fate). By extending these types of analyses to later and later stages in development and by proceeding in a flow-chart like manner from very general cases(commitment between mesoderm and ectoderm), to very specific distinctions (commitment between different types of neurons), an organized pattern of differentiation can be conceptualized. By systematically testing the in vivo responses of cells to various conditions at different times in development, we hope to better understand how cell identity is conferred and how a vertebrate, such as the zebrafish, organizes the emergence of its complex body plan.
Another tool we can use in the study of cell identity is the isolation and characterization of mutations that affect the patterning of the zebrafish body plan. For example, the spadetail mutant specifically lacks segmented somites in the trunk region; the no tail mutant fails to form a differentiated notochord; and the cyclops mutantlacks a specialized group of ventral cells in the neural tube called floor plate cells. We plan to further characterize these and similar mutations using a variety of embryological and molecular techniques in order to better understand the cellular and biochemical interactions that lead to the expression of definitive cell fates.
The embryo of the zebrafish is an excellent preparation in which to study many aspects of development. Cells of zebrafish are relatively large, optically clear, and accessible at all stages of development to experimental manipulations such as the microinjection of lineage tracer molecules, cell ablations, and cell transplantations. The zebrafish embryo also has a strong background of genetic analyses, and several interesting mutations have been isolated. In addition, many molecular techniques are becoming increasingly routine in the zebrafish system.
Because zebrafish embryos are optically transparent, it is easy to label individual cells with fluorescent lineage tracers
and follow their development using low light level video time-lapse techniques. By using these methods, Kimmel and his coworkers were able to construct a "fate map" for the zebrafish at gastrulation. A fate map, which is a puzzling together of the various cell lineages of an organism, allows one to accurately predict the identity of the progeny cells produced by a given precursor cell, and therefore is a useful reference model for normal development.
We are interested in understanding how and when individual cells of the early embryo become "committed," that is, irreversibly restricted to expressing a particular cellular identity. The elucidation of the zebrafish fate map has allowed us to perform precise and reproducible
experimental manipulations for the purpose of disturbing the normal cellular processes in defined ways. By studying the effects of these
manipulations on development, we hope to gain insights into the manner by which cellular identity is specified and maintained.
For instance, we now have techniques to transplant individual embryonic cells from one fate map region of a labeled donor embryo to a different region within an unlabeled host. The purpose of these manipulations is to see if the transplanted cell would later express a fate appropriate for its new position (in which case it was still pluripotent and uncomitted to any particular fate), or if it would retain the fate of its original position even though moved to a new location (in which case it could be characterized as committed to its original fate). By extending these types of analyses to later and later stages in development and by proceeding in a flow-chart like manner from very general cases(commitment between mesoderm and ectoderm), to very specific distinctions (commitment between different types of neurons), an organized pattern of differentiation can be conceptualized. By systematically testing the in vivo responses of cells to various conditions at different times in development, we hope to better understand how cell identity is conferred and how a vertebrate, such as the zebrafish, organizes the emergence of its complex body plan.
Another tool we can use in the study of cell identity is the isolation and characterization of mutations that affect the patterning of the zebrafish body plan. For example, the spadetail mutant specifically lacks segmented somites in the trunk region; the no tail mutant fails to form a differentiated notochord; and the cyclops mutantlacks a specialized group of ventral cells in the neural tube called floor plate cells. We plan to further characterize these and similar mutations using a variety of embryological and molecular techniques in order to better understand the cellular and biochemical interactions that lead to the expression of definitive cell fates.
Lab Members
| Ahn, Dae-gwon Post-Doc | Byrd, Shannon Graduate Student | Vickers, Sarah Graduate Student |