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The stages of generation of the house spider
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When the body of vertebrates is formed, the cell colony actions are important for determining which part of the egg becomes the dorsal area. These cells excrete the protein chordin that elicits the spine and other parts of the dorsal structure. The cells themselves become the notochord, which is later replaced by the backbone. In the non-vertebrate housefly, however, it has been learned that the sog molecule, which resembles chordin, has the role of determining the size of the ventral nerve. No structure that corresponds to the notochord has been found, however. Did the notochord suddenly appear during the course of evolution?
We found a hint for answering this question in the spider. A small cell group in the spider embryo called the cumulus excretes a molecule called dpp. It has been learned that this creates the ventral medial line and the central nerve by localizing the expression of the sog genes on the ventral area. This closely resembles the pattern for creating the notochord and the spine in vertebrates. This is unlikely to be an accidental resemblance.
Perhaps the common ancestor to the spider and humans determined the body’s central axis through conversations conducted between cells with dpp and sog. Did the process of evolution, headed in the direction of vertebrates, incorporate that notochord as the central axis inside the body, later to create bones around it? We would like to verify this theory in the future.
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Biohistory Journal, Autumun, 2006
