生長相關蛋白-43 (GAP-43) 會高度表現於正在發育與再生的神經元軸突生長錐 (axonal growth cone)，其功能為神經元軸突延伸之誘導因子，因此在哺乳與兩棲類動物的研究中，GAP-43常被運用來作為評估個體之神經元發育與再生的生物標記，然而至今魚類相關研究甚少。為了解石斑魚神經發育與再生情形，本篇研究選殖出石斑魚 (Epinephelus spp.)之GAP-43基因作為生物標記，並分析魚苗與幼魚各時期神經發育及視神經損傷後修復期之GAP-43基因表現情形。研究結果顯示隨著魚齡增加，GAP-43 基因表現量會逐漸下降；而在視神經損傷模式中，GAP-43基因表現量會再度升高，於損傷後5天到達高峰，最大表現量為損傷前的22.60倍，接著在損傷後30天內逐漸下降至正常值。實驗中亦利用視神經損傷模式使魚體視神經再度處於高度生長階段，模擬魚苗時期神經生長情形，並以神經壞死病毒 (Nervous necrosis virus, NNV) 進行腹腔攻毒實驗，以了解魚類神經發育與再生與神經趨性病毒NNV的關係。點帶石斑魚和龍膽石斑魚實驗結果皆顯示當視神經再生時，其眼睛NNV平均表現量高於視神經未再生組，並可高達14.25倍。由免疫組織化學染色的結果亦發現，GAP-43蛋白於石斑魚眼部表現位置與NNV外鞘蛋白表現位置相仿。
由以上結果證實，本篇選殖之石斑魚GAP-43基因與其他物種之GAP-43重要的基因特性類似，可於神經再生與發育時期高度表現，故GAP-43可在石斑魚中作為一良好的神經發育與視神經再生之生物標記。且利用GAP-43作為生物標記，其結果推測點帶石斑魚與龍膽石斑魚之神經元的成熟度與NNV感受性有關。

Growth-associated protein-43 (GAP-43) has been found that is highly expressed in developing and regenerating axonal growth cones. GAP-43 is involved in regulating growth of axon terminals. Therefore, GAP-43 is a neuron-specific bio-marker extensively used to detect developing and regenerating nervous system in mammals and amphibians. However, studies in fish are scarce. To realize the neuronal development and regeneration in grouper (Epinephelus spp.), grouper GAP-43 was cloned in this study and used as a bio-marker to investigate grouper neuronal development in larval stage, juvenile stage and optic nerve regeneration after optic nerve injury. Results showed that GAP-43 mRNA expression decreased as age increased. After optic nerve transection, GAP-43 mRNA expression peaked at 5th day reaching to 22.60-fold compared with the control level without optic nerve injury and gradually decreased to the control level at 30th day. Optic nerves in fish returned to the high growth state through optic nerve transection to mimic the neuronal growth during larval stage. After optic nerve transection, groupers were NNV challenged by intraperitoneal injection to investigate the relationship between fish neuronal growth and the susceptibility to NNV infection. Results in orange-spotted grouper and giant grouper both showed that NNV RNA2 average expression level in eye during optic nerve regeneration was higher than eye without optic nerve regeneration that could increase to 14.25-fold. In grouper, immunohistochemistry (IHC) results indicated that the localization area in eye of GAP-43 protein was similar to NNV coat protein.
Our results show the characteristics of grouper GAP-43 are similar to other species that GAP-43 is highly expressed in developing and regenerating stages. GAP-43 is an ideal bio-marker for study of neuronal development and optic nerve regeneration in grouper. Using GAP-43 as a bio-marker, the results also suggest the susceptibility of grouper to NNV infection may be related to the neuronal maturity.

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