De Tomaso Laboratory of Stanford University
De Tomaso Laboratory of Stanford University
The genetic and developmental processes underlying recurring asexual budding (regeneration)Botryllus adults undergo a week long, asexual budding cycle called blastogenesis. Each week new buds develop via a process involving components from the blood as well as the body wall of the existing parental zooid. As each individual is created de novo with these components, every week a Botryllus colony is in the process of regenerating every major organ system, including a heart, gut, a primitive thyroid, nerve cells, as well as gametes. At the end of the 7 day life of the zooid, it is destroyed by a massive apoptotic event which is called takeover, the newly developed bud becomes the adult zooid, and the process repeats itself: the body of Botryllus is actually a transient structure that is completely regenerated in a weekly cycle. This regenerative potential does not exist in any other chordate and the developmental and genetic programs that underlie asexual budding are completely unknown. Is this process more akin to regenerations, or normal development? What Hox genes are involved, how is patterning of the asexual bud accomplished, and are they the same genes that are responsible for development in the tadpole larva? We have the tools to integrate both developmental and genomic studies using this organism. Furthermore, we have recently found that siRNA knockout can be efficiently achieved by merely adding the reagents to the seawater the individuals inhabit. This will allow us to analyze asexual reproduction using a high-throughput RNAi screen, as the cyclical nature of asexual development ensures the majority of proteins must be turning over during the budding process. We have initiated these studies and have cloned a number of Hox genes, and are currently localizing their expression during asexual budding, as well as knocking function using RNAi. Genomic clones of these genes (both BACs and Fosmids) have been cloned and are currently being analyzed. |
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| A Nomarski image of asexual budding early in the weekly cycle. The secondary bud has just formed into a blastula-like structure and will soon begin further development. The primary bud is finishing organogenesis. (Picture by Brett Staahl) |