Kuroda Megumi, Nagasaki Toshihiro, Koito Tomoko, Hongo Yuki, Yoshida Takao, Maruyama Tadashi, Tsuchida Shinji, Nemoto Suguru, Inoue Koji
Biol Bull. 2021 Feb;240(1):34-40. doi: 10.1086/712396. Epub 2021 Feb 9.
AbstractVesicomyid clams, which inhabit deep-sea hydrothermal vents and hydrocarbon seeps, are nutritionally dependent on symbiotic, chemoautotrophic bacteria that produce organic matter by using hydrogen sulfide. Vesicomyid clams absorb hydrogen sulfide from the foot and transport it in their hemolymph to symbionts in the gill. However, mechanisms to cope with hydrogen sulfide toxicity are not fully understood. Previous studies on vent-specific invertebrates, including bathymodiolin mussels, suggest that hypotaurine, a precursor of taurine, mitigates hydrogen sulfide toxicity by binding it to bisulfide ion, so as to synthesize thiotaurine. In this study, we cloned cDNAs from the vesicomyid clam for the taurine transporter that transports hypotaurine into cells and for cysteine dioxygenase and cysteine-sulfinate decarboxylase, major enzymes involved in hypotaurine synthesis. Results of reverse-transcription polymerase chain reaction indicate that mRNAs of these three genes are most abundant in the foot, followed by the gill. However, hypotaurine and thiotaurine levels, measured by reverse-phase high-performance liquid chromatography, were low in the foot and high in the gill. In addition, thiotaurine was detected in hemolymph cells. Hypotaurine synthesized in the foot may be transported to the gill after binding to bisulfide ion, possibly by hemolymph cells.
摘要
生活在深海热液喷口和碳氢化合物渗漏处的泡蛤，在营养上依赖于共生的化学自养细菌，这些细菌利用硫化氢产生有机物。泡蛤从足部吸收硫化氢，并通过血淋巴将其运输到鳃中的共生体。然而，应对硫化氢毒性的机制尚未完全了解。先前对包括深海贻贝在内的特定喷口无脊椎动物的研究表明，牛磺酸的前体次牛磺酸通过将其与二硫化物离子结合来减轻硫化氢毒性，从而合成硫代牛磺酸。在本研究中，我们从泡蛤中克隆了将次牛磺酸转运到细胞中的牛磺酸转运体以及参与次牛磺酸合成的主要酶——半胱氨酸双加氧酶和半胱氨酸亚磺酸脱羧酶的cDNA。逆转录聚合酶链反应结果表明，这三个基因的mRNA在足部含量最高，其次是鳃。然而，通过反相高效液相色谱法测定，次牛磺酸和硫代牛磺酸水平在足部较低，在鳃中较高。此外，在血淋巴细胞中检测到了硫代牛磺酸。在足部合成的次牛磺酸可能在与二硫化物离子结合后被运输到鳃中，可能是通过血淋巴细胞。
