Figure 7

Liver-specific Mtm1 expression rescues the cholestatic phenotype of mtm zebrafish.

The fabp:mtm1-GFP transgene was introduced into the mtm-mutant zebrafish line. The resulting fish were analyzed for morphological and functional changes associated with cholestasis. (A) Crossing scheme for introducing the fabp:mtm1-gfp transgene into the mtm zebrafish line. Transgenic fish were outcrossed twice to mtm1+/Δ8 fish, resulting in clutches of larvae for experiments that contained WT and mtm fish with and without the transgene. (B) A BODIPY assay was used to measure bile flux (WT – GFP = 88%, WT + GFP = 96%, mtm – GFP = 30%, mtm + GFP = 65%). In the mtm transgene–positive group, there were more mtm mutants with normal bile flux when compared with the mtm transgene–negative group, as measured by positive gall bladder fluorescence (P = 0.0532, 1-sided Fisher’s exact test). (C) Visualization of liver-specific Mtm1 expression from the fabp:mtm1-GFP transgene. In WT fish, Mtm1 localized to the plasma membrane and to subapical structures that were Mdr1⁺ and Rab11⁺ by immunostaining (top two rows). In mtm zebrafish, hepatocyte-expressed Mtm1 restored bile canalicular architecture and bile transporter expression to the bile canaliculi. Coimmunostaining of whole-mount embryos revealed the reexpression of Mdr1 puncta in 7 dpf mtm larvae. Scale bars: 10 μm.