Background/Aim: Previous studies have shown that fibroblast growth factors (FGFs) are involved in the process of liver injury repair. Liver regeneration after partial hepatectomy (PH) is impaired in transgenic mice expressing dominant-negative FGFR2b in hepatocytes. Although FGF7, a ligand specifically bound to FGFR2b, is expressed by activated hepatic stellate cells (HSCs) in fibrotic livers, the expressions and functions of FGF7 and FGFR2b after PH remain unexplored. Therefore, this study sought to examine the potential role of FGF7 signaling during liver regeneration. Methods: We examined the expression of FGF7 and FGFR2b in normal and regenerating livers. Effects of FGF7 on hepatocytes were examined in vitro using primary hepatocyte culture with FGF7 recombinant protein and in vivo by hydrodynamic-based gene transfer method. Results: We found that FGF7 expression was increased according to the activation status of HSCs after PH. The receptor, FGFR2b, was also increased in hepatocytes during liver regeneration. In vitro treatment with FGF7 protein activated ERK1/2 and promoted proliferation of hepatocytes isolated from regenerating livers. In vivo overexpression of exogenous FGF7 could notably promote hepatic proliferation and activate MAPKs after PH. Conclusion: This study suggests a role for activated HSC-expressed FGF7 in stimulating FGF signaling pathways in hepatocytes and regulating liver regeneration.

Many organs in vertebrates are left-right asymmetrical located. For example, liver is at the right side and stomach is at the left side in human. Fibroblast growth factor (Fgf) signaling is important for left-right asymmetry. To investigate the roles of Fgfr2 signaling in zebrafish left-right asymmetry, we used splicing blocking morpholinos to specifically block the splicing of fgfr2b and fgfr2c variants, respectively. We found that the relative position of the liver and the pancreas were disrupted in fgfr2c morphants. Furthermore, the left-right asymmetry of the heart became random. Expression pattern of the laterality controlling genes, spaw and pitx2c, also became random in the morphants. Furthermore, lefty1 was not expressed in the posterior notochord, indicating that the molecular midline barrier had been disrupted. It was also not expressed in the brain diencephalon. Kupffer's vesicle (KV) size became smaller in fgfr2c morphants. Furthermore, KV cilia were shorter in fgfr2c morphants. We conclude that the fgfr2c isoform plays an important role in the left-right asymmetry during zebrafish development.

In mammals, fibroblast growth factor (FGF) signaling controls liver specification and regulates the metabolism of lipids, cholesterol, and bile acids. FGF signaling also promotes hepatocyte proliferation, and helps detoxify hepatotoxin during liver regeneration after partial hepatectomy. However, the function of Fgf in zebrafish liver is not yet well understood, specifically for postnatal homeostasis. The current study analyzed the expression of fgf receptors (fgfrs) in the liver of zebrafish. We then investigated the function of Fgf signaling in the zebrafish liver by expressing a dominant-negative Fgf receptor in hepatocytes (lfabp:dnfgfr1-egfp, lf:dnfr). Histological analysis showed that our genetic intervention resulted in a small liver size with defected medial expansion of developing livers in transgenic (Tg) larvae. Morphologically, the liver lobe of lf:dnfr adult fish was shorter than that of control. Ballooning degeneration of hepatocytes was observed in fish as young as 3 months. Further examination revealed the development of hepatic steatosis and cholestasis. In adult Tg fish, we unexpectedly observed increased liver-to-body-weight ratios, with higher percentages of proliferating hepatocytes. Considering all these findings, we concluded that as in mammals, in adult zebrafish the metabolism of lipid and bile acids in the liver are regulated by Fgf signaling. Disruption of the Fgf signal-mediated metabolism might indirectly affect hepatocyte proliferation.

During organogenesis, the issue of size regulation is as important as shape and differentiation. We propose that the regulation of the dimensions of the epithelium and its appendages (length, width, thickness) are based on regulation of cell numbers in specific sites, reflecting the input and output of cells in that region. This process is in turn regulated by the flow from the domain of proliferating cells to the domain of postmitotic differentiated cells. When the homeobox gene Msx-2 is over-expressed in transgenic mice under the control of the CMV promoter, the epidermis is thickened with hyperproliferation and hyperkeratosis. Hairs are shorter and the matrix region is shrunken. We suggest that Msx-2 may be one of the regulators involved in the control of organ size, and the above phenotypes are the manifestations of an increased cellular flow from proliferation domain to differentiation domain in the tissue.

The zebrafish (Danio rerio) is a versatile model organism that has been used in biomedical research for several decades to study a wide range of biological phenomena. There are many technical advantages of using zebrafish over other vertebrate models. They are readily available, hardy, easy, and inexpensive to maintain in the laboratory, have a short life cycle, and have excellent fecundity. Due to its optical clarity and reproducible capabilities, it has become one of the predominant models of human genetic diseases. Zebrafish research has made rapid strides in the United States and Europe, but in India the field is at an early stage and many researchers still remain unaware of the full research potential of this tiny fish. The zebrafish model system was introduced into India in the early 2000s. Up to now, more than 200 scientific referred articles have been published by Indian researchers. This review gives an overview of the current state of knowledge for zebrafish research in India, with the aim of promoting wider utilization of zebrafish for high level biological studies.