The goal of this research is to determine if an "organizer" for the development of the posterior body of the zebrafish embryo exists and if so, whether it is developmentally and/or molecularly related to the organizer region responsible for the proper patterning of head and trunk regions. The "Spemann Organizer" has been well documented as playing a necessary role in the early development of perhaps all vertebrate embryos. However, classical observations as well as recent genetic studies have suggested that the development of the tail region of vertebrates may be under separate controls from that of the head and trunk region. In addition, fate mapping and molecular expression studies show that development of the posterior body involves mechanisms significantly different from development of the more anterior regions. The development of the vertebrate posterior body will be studied in the following manner:
I) It will be determined if a tail organizer exists and whether it is functionally related to the organizer region of the trunk. Transplantation methods will be used to move zebrafish tailbud tissues into younger host embryos to examine organizer-specific activities both in terms of tissue interactions (i.e. the formation of a secondary posterior axis) and the induction of "immediate response" genes indicative of posterior tissue formation. In a systematic fashion, it will be determined which specific regions of the tailbud are responsible for these activities during normal posterior development.
II) It will be determined if specific tailbud cell movements and/or tissue regions are perturbed in mutant lines of zebrafish which display posterior body abnormalities. A high-quality fate map has been previously produced and used to extensively analyze the cell movements and the expression of genes during posterior body development in the wild-type zebrafish embryo. This fate map information will be utilized to compare the posterior development of wild-type embryos with that of mutant zebrafish; in particular the no tail, spadetail, floating head, mercedes and lost-a-fin mutations. Abnormalities indicative of defective organizer activity and/or downstream tissue patterning will be studied in order to determine how they are responsible for causing these mutant phenotypes.
