淡水長臂大蝦大顎器官離體培養下類青春激素 MF 之合成與調控

Abstract

甲殼類類青春激素MF(methyl farnesoate）是由大顎器官(mandibular organ, MO）所合成與分泌。本報告以淡水長臂大蝦為實驗對象，建立大顎器官之離體培養系統，以TLC、GC/MS、HPLC等層析法定性分析大顎器官離體培養下的產物MF。其結果證明所取組織可分泌MF，表示MO解剖位置無誤，而MF之定量分析則以放射性化學分析法（Radiochemical Assay, RCA）進行，實驗中雌性淡水長臂大蝦之MF合成速率約為3.0±1.3pmol/hr/MO。 在MF合成之上位調控方面，剪單邊眼柄三天的個體，其合成MF之能力為未剪眼柄者之2.3倍；而若於剪眼柄第三天取大顎器官與眼柄萃液共同培養反應，則MF之合成復下降為與未剪眼柄者同，可見眼柄內含之物質具有抑制MF合成之調節作用。而細胞內訊息傳遞有關分子例如cAMP以及cGMP方面，若於培養液中加入其類似物（8-Br-cAMP及8-Br-cGMP）、cAMP或cGMP合成酵素之活化劑（forskolin或SNP）等，發現這些藥物在此離體培養系統中亦具有抑制MF合成之影響，因此推測cAMP與cGMP皆參與調控MF合成之作用機制。綜上所述，MF的合成應受到某種嚴密的上位調控，而本報告所建立的大顎器官離體檢測系統，對於分析眼柄內神經激素功能與大顎器官內訊息傳遞模式等研究，提供一直接而有效的工具。

It is established that the mandibular organ (MO) of decapod crustaceans synthesizes and secretes methyl farnesoate (MF). In this report, MOs of the giant freshwater prawn, Macrobrachium rosenbergii were investigated by in vitro incubation system. Products of MO were identified by TLC, GC/MS and HPLC. Secretion of MF from the dissected MOs confirmed the site of MO in M rosenbergii. Radiochemical assay (RCA) was used to quantify in vitro MF synthesis. The rate of MF synthesis in female M. rosenbergii was 3.0±1.3 pmol/hr/MO. With regard to the regulation of MF synthesis, the synthetic potential of MF on the third day of unilaterally eyestalk ablation was about 2.3 times greater than that of intact. On the other hand, this effect was reduced by addition of crude eyestalk extract in the medium. These results suggested that MF synthesis might be modulated by neuropeptides produced and released from the X-organ sinus gland complex of the eyestalk. As to the intracellular signal transduction pathway of the regulation, in vitro treatment of MO with 8-Br-cAMP (cAMP analog), 8-Br-cGMP (cGMP analog), forskolin (adenylate cyclase activator) and SNP (sodium nitroprusside, guanylate cyclase activator) all had inhibitory effect on MF synthesis. Therefore, cAMP and cGMP might act as second messengers in the regulation of MF synthesis. According to these in vitro data, the synthesis of MF should be under some precise regulation and this MO bioassay system can be a useful tool for studies on neurohormonal regulation and its signal transduciton.