Identification and functional expression of two subtypes of glycerol-3-phosphate acyltransferase differently regulating triacylglyceride synthesis during ovary development in Chinese mitten crab, Eriocheir sinensis

Triacylglycerides (TAG) are a pivotal nutrient for crustacean reproduction, rapidly accumulating in gonads and hepatopancreas during the ovary development. Glycerol-3-phosphate acyltransferase (GPAT) is the enzyme catalyzing the first step in TAG synthesis. In the present study, two EsGPATs subtypes (EsGPAT1 and EsGPAT2) were identified and characterized. The transcript of EsGPAT1 was highly expressed in thoracic ganglia, hepatopancreas and ovary, while EsGPAT2 was mainly detected in nervous tissues and intestine. During the ovary development, in hepatopancreas, the expression levels of EsGPAT1 increased from Stage I to its maximum at Stage IV and then declined sharply. The transcription levels of EsGPAT2 were highest at Stage I and then gradually declined to reach its minimum at Stage IV. In ovaries, the EsGPAT1 expression levels increased from Stage I to reach its maximum at Stage IV and then declined. The transcription levels of EsGPAT2 reached the peak at Stage I and then declined to the minimum at Stage III. In situ hybridization revealed they were both located in the F cells and R cells of hepatopancreas and all types of cells at Stage I, the follicle cells and the exogenous vitellogenic oocytes at Stage III and nearly mature oocytes at Stage IV of the ovary. In addition, the knockdown of EsGPAT1 downregulated the expression levels of downstream genes in TAG synthesis pathway, but it was not observed in RNAi treatment group of EsGPAT2. These results indicate that the two EsGPATs identified have different roles in TAG metabolism during the ovarian development of E. sinensis.