Studies on endocrine system of amphioxus in comparison with vertebrates

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In order to consider the evolution of the endocrine mechanism to vertebrates, the endocrine mechanism of amphioxus belonging to the same phylum Chordata as vertebrates was investigated. There is a common sex steroidogenic pathway and 5α-reduced steroids is main in amphioxus. Furthermore, gene expressions of glycoprotein hormones, neurohypophyseal hormone, estrogen receptor and gonadotropin-releasing hormone receptors were shown in nerve cells of a nerve cord. These results suggest that many endocrine substances of amphioxus are homologous to those of vertebrates, but synthesized in a nerve cord as a neuroendocrine system.