Structure and function of brain and nerve cord-endocrine system in amphioxus

从形态学和分子生物学的角度研究了脑神经元和内分泌器官系统从无脊椎动物到脊椎动物的进化过程。文昌鱼是最接近脊椎动物的无脊椎动物，具有原始的脑和垂体、甲状腺、肾脏等内分泌器官。通过同源性搜索，从7，800个EST克隆中找到了内分泌基因。其中神经肽类包括RFamide、神经肽Y、降钙素等，甾体生成酶类包括P450 SCC、P450 C17和17α，20β-HSD。用原位杂交技术检测了部分神经肽克隆在神经索中的定位。编码类固醇生成酶的基因在神经索中的神经细胞和神经元中表达。雌激素合成酶、3β-HSD和芳香化酶在EST克隆中不表达，在卵巢中表达。用放射免疫分析法测定孕酮和17β-雌二醇的浓度，结果表明，在繁殖季节，孕酮和17β-雌二醇的浓度升高。从EST序列中获得视蛋白基因，并对其在神经索中的表达和吸收光谱进行研究。光感受器在神经细胞中的存在被认为是光刺激诱导神经元活化与信号传导之间的可能联系。本研究表明文昌鱼的生殖可能受性类固醇激素的调控，并可能通过神经系统受到光的刺激。进一步研究文昌鱼神经索和性腺中性类固醇的功能，可能揭示脊椎动物脑中神经类固醇的功能。

The evolution of the brain-neuron and endocrine organ system from invertebrate to vertebrate has been studied on morphological and molecular aspects in changes of their organs. Amphioxus is the closest invertebrate to vertebrate and considered to possess primitive brain and endocrine organs such as pituitary, thyroid and kidney and so on. Sequences of expressed genes in amphioxus were analyzed by EST conducted from amphioxus nerve cord. Endocrine genes were found from 7,800 EST clones by a homology search. They were neuropeptides including RFamide, neuropeptide Y, and calcitonin and so on, and steroidogenic enzymes including P450scc, P450c17 and 17α, 20β-HSD. Some neuropeptide clones were detected their localizations in nerve cord by in situ hybridization. Genes encoded steroidogenic enzymes were expressed in nerve cells in nerve cord and neurons. Steroidogenic enzymes, 3β-HSD and aromatase were not fond in EST clones, and detected in ovary by using immunohistochemistry. Concentrations of progesterone and estradiol-17β were measured by RIA and increased in breeding season. Opsin gene obtained from EST sequences was studied on the expression in nerve cord and absorbance spectrum. The existence of photoreceptor in nerve cells was suspected the possibility of relations of activation and signaling of neuron induced by photo-stimulation. This study showed the possibility that reproduction in amphioxus was regulated by sex steroids and might stimulate by light through nerve system. In further study, functions of sex steroids in nerve cord and gonad in amphioxus might reveal the neurosteroid function in vertebrate brain.