The organogenesis is a complex and invisible process in vertebrate. However, depending on transgenic technology, cell fate tracing and tissue-specific imaging have highlighted some significantly conserved processes essential for vertebrate endoderm development and organ formation. Several transgenic zebrafish lines for liver development studies had been obtained in the first decade of this century, but no transgenic GFP zebrafish lines that mark the through liver development and organogenesis have been reported.  

Recently, on the basic studies of cloning the 14kDa apolipoprotein gene, Apo-14 and analyzing its expression pattern in hermaphroditic orange-spotted grouper (Epinephelus coioides) (Zhou et al., 2005) and polyploid gibel carp (Carassius auratus gibelio) (Xia et al., 2008), Prof. Gui Jianfang and his colleagues from the Research Group of Fish Developmental Genetics and Cell Engineering at Institute of Hydrobiology, Chinese Academy of Sciences (IHB) subsequently examined spatiotemporal expressionof Apo-14 in zebrafish embryogenesis, isolated the promoter sequence, developed an Apo-14 promoter-driven transgenic zebrafish Tg (Apo14: GFP) and finally observed maternal expression and post-fertilization translocation of Apo-14 promoter-driven GFP in transgenic zebrafish line.  

Moreover, by out-crossing the Tg (Apo14: GFP) male to the wild type female, Prof. Gui's group traced the onset expression of Apo-14 promoter-driven GFP and developmental behavior of the expressed cells in early heterozygous embryos. Interestingly, the Apo-14 promoter-driven GFP is initially expressed around YSL beneath the embryo body at 10hpf when the embryos develop to tail bud prominent. In about 14-somite embryos at 16-17hpf, a typical “salt-and-pepper” expression pattern is clearly observed in YSL around the yolk sac. Then, a green fluorescence dot begins to appear between the notochord and the yolk sac adjacent to otic vesicle at about 20hpf, which is later demonstrated to be liver primordium that gives rise to liver.  

Furthermore, the dynamic progression of liver organogenesis in the Tg (Apo14: GFP) zebrafish was investigated, because the Apo-14 promoter-driven GFP is sustainably expressed from hepatoblasts and liver progenitor cells in liver primordium to hepatocytes in the larval and adult liver. Additionally, the similar morphology between the liver progenitor cells and the GFP-positive nuclei on the YSL suggests that they might originate from the same progenitor cells in early embryos. Overall, the current study provides a new transgenic fish line that can mark the whole liver development and organogenesis from the early endoderm cells to the entire liver organogenesis. 

This work was funded by the National Key Basic Research Program and Open Project of State Key Laboratory of Freshwater Ecology and Biotechnology. It was mainly finished by Dr. Wang Rui et al. under the supervision of Prof. Gui Jianfang. The paper was published in PLoS One on July 22, 2011. 

Related link: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0021057