The Hepatic Caecum Of Amphioxus (Branchiostoma Belcheri.)-Localization Of Vitellogenin And Toxicities Of Cadmium And Copper To Amphioxus

Amphioxus or lancelet, a cephalochordate, is the extant invertebrate most closely related to the proximate ancestor of vertebrate, and has long been regarded as the model animal for insights into the evolution of vertebrate and developmental homology analysis. In this paper, it is for the first time to compare the amphioxus hepatic diverticulum to the vertebrate liver from two aspects: synthesis of vitellogenin and toxicity of heavy metals, with an aim to provide an evidence of physiological functionality supporting the hypothesis that the digestive caecum of an amphioxus-like ancestor is a precursor of vertebrate liver.Vitellogenin (Vg) is the egg yolk protein precursor, which is specifically synthesized in the vertebrate liver and secreted into the bloodstream, and transported by circulation to the ovary, where it is taken up by the growing oocytes and forms their yolk protein. The localization of vitellogenin remains untested in amphioxus. Western blotting analysis showed that mouse anti-amphioxus Vg sera cross-reacted with the crude extracts of the hepatic diverticulum and ovary, and humoral fluids including blood and coelomic fluid from specimens of Branchiostoma belcheri. The positive band all had an apparent molecular mass of approximately 320 kDa, which corresponds to the molecular weight reported for amphioxus Vg previously by Sun & Zhang (2001), and confirms our previous proposal that Vg exists in the oocytes of amphioxus as an uncleaved protein. Similarly, immunohistochemical staining also revealed that vitellogenin is localized in the hepatic diverticulum, sub-intestinal vessels, and ovary in amphioxus. The hepatic diverticulum of amphioxus, like the vertebrate liver, synthesizes vitellogenin, suggesting that amphioxus hepatic diverticulum is functionally equivalent to the vertebrate liver in respect of the synthesis of this compound. This agrees with the idea that amphioxus hepatic...