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Title: Developmental biology of the pterobranch hemichordate Rhabdopleura compacta
Author: Sato, Atsuko
ISNI:       0000 0001 3553 5150
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2008
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The aim of this research is to gain new insights into the evolution of deuterostomes through molecular developmental investigation of pterobranchs. This thesis consists of three major parts. In the first part, I investigated the seasonal reproductive activity of the pterobranch species Rhabdoplellra compacta. By analyzing large numbers of specimens for two years, I found that their reproductive activity has a peak in June. In the second part, I investigated the origin of vertebrate left-right axis patterning using anatomical as well as molecular studies on R. compacta. I found that R. compacta indeed have anatomical left-right asymmetry in the body. However, contrary to the traditional description, the direction was random, rather than directional as traditionally described. Together with further molecular analyses and previous morphological studies in enteropneusts, I suggest that precise left-right patterning already existed before the divergence of deuterostomes, but underwent degeneration during the evolution of the hemichordate lineage. The molecular analyses brought about two unexpected discoveries. One is that the expression patterns of the gene I examined were completely different from those of enteropneusts. Importantly, expression of the hedgehog gene in pterobranchs was found in the dorsal midline as in chordates, suggesting that the dorsal side of pterobranchs may be comparable to the dorsal side of chordates. The other is that there are unusual mutations in the autoproteolytic cleavage region of hedgehog proteins in the hemichordate lineage. In the third part, I analyzed whether these mutations alter efficiency of autoproteolytic cleavage and the signaling function, using Drosophila genetics. It was found that an enteropneust-type mutation decreases the efficiency of autoproteolytic cleavage whereas a pterobranch-type does not. Since this autoproteolytic cleavage is essential for the signaling function of hedgehog proteins, I suggest that hedgehog underwent unique functional evolution in the enteropneust lineage, which requires less efficiency of signaling function.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available