Functional differentiation analysis of duplicated mlpha gene in Oujiang color common carp ( Cyprinus carpio var. color ) on colour formation

Abstract

Melanophilin (mlph) encodes a subfamily of Rab effector proteins which is an important gene for the transportation of mature melanosomes. Duplicated mlpha gene (mlpha1 and mlpha2) of Oujiang color common carp (Cyprinus carpio var. color) was firstly identified in the present study, which includes an open reading frame (ORF) length of 1713 bp and 1536 bp, encoding 570 and 511 amino acids respectively. Spatial and temporal expression, in situ hybridization and disruption experiments were conducted to explore the functional differentiation of mlpha (mlpha1 and mlpha2) during the melanin transport process of Oujiang color common carp. Distinct expression pattern of mlpha1 and mlpha2 were identified, and the expression level of mlpha1 in red skin of whole red with black patch (RB-R) and white skin of whole white with black patch (WB-W) was significantly lower than their corresponding black skin of RB and WB (RB-B and WB-B). On the contrary, the expression level of mlpha2 in RB-R and WB-W was significantly higher than their corresponding black skin (RB-B and WB-B). Mlpha2 was highly expressed in the “Whole red” (WR) skin, and mlpha1 was lowly expressed in the WR. Meanwhile, abundant positive ISH hybridization signals of mlpha2 were identified in 5 days post-hatch larvae (5dph) of WR. The high mutation rate of mlpha1 and mlpha2 genes resulted in a significant dilution phenotype, while the low mutation rate led to partial skin to appear discoloration phenomenon of Oujiang color common carp (RB and WB). The findings indicated that mlpha is an indispensable functional gene that may participate in the transportation of pigments and functional differentiation may exist between mlpha1 and mlpha2 after duplication. Mlpha1 may be mainly involved in the transportation of melanin, and mlpha2 may also participate in the transportation of other pigments.