title: The expression of VILL protein is hypoosmotic-dependent in the lamellar gill ionocytes of Otocephala teleost fish, Chanos chanos.
abstract: Milkfish, a species within the primitive teleost lineage Otocephala, can survive in water conditions ranging from hypo- to hyper-saline. This study explored the effects of environmental salinity on apical morphologies of ionocytes and the expression of villin homologs in the gills of milkfish acclimated to either seawater (SW) or fresh water (FW). Scanning electron microscopy revealed that the ionocytes in the gill filaments of SW and FW milkfish, respectively, cellular apical morphologies were hole-type and squint-type. The flat-type ionocytes were observed in the gill lamellae of FW milkfish. Furthermore, apical surfaces of some lamellar ionocytes exhibited microvilli. Villin 1 is a microvilli marker expressed in the epithelial cells of various vertebrates. In the phylogenetic tree of villin 1 homologs, primitive teleosts exhibit villin 1-like (VILL) and villin 1 proteins. Two mRNA sequences, villin 1 and VILL, were identified from the milkfish transcriptome by next generation sequencing. Low but constant expression of villin 1 (gene and protein) was observed in the gills for both SW and FW fish. VILL gene and protein expression levels in the gills were higher in FW fish, compared to SW fish. Double immunofluorescence staining demonstrated that VILL protein was present in some lamellar ionocytes of FW milkfish, but not in the filament ionocytes of either FW or SW milkfish. Taken together, these findings indicated that the VILL expression of ionocytes is hypoosmotic-dependent. The VILL might be involved in the formation of microvilli in the lamellar ionocytes for hyperosmoregulation of the milkfish.
authors: Tainan Hydraulics Laboratory, National Cheng Kung University, Tainan 709, Taiwan.
authors: Chao-Kai
authors: CK
authors: Kang
authors: Department of Life Sciences, National Chung-Hsing University, Taichung 402, Taiwan.
authors: Chia-Shian
authors: CS
authors: Lin
authors: Department of Life Sciences, National Chung-Hsing University, Taichung 402, Taiwan.
authors: Yao-Chung
authors: YC
authors: Hu
authors: Institute of Life Science, Central Taiwan University of Science and Technology, Taichung 406, Taiwan.
authors: Shu-Chuan
authors: SC
authors: Tsai
authors: Department of Life Sciences, National Chung-Hsing University, Taichung 402, Taiwan; Department of Biological Science and Technology, China Medical University, Taichung, 404, Taiwan. Electronic address: thlee@email.nchu.edu.tw.
authors: Tsung-Han
authors: TH
authors: Lee
mesh_terms: D000818:Animals; D005399:Fishes / Q000378:metabolism*; D005880:Gills / Q000166:cytology / Q000378:metabolism*; D008840:Microfilament Proteins / Q000378:metabolism*; D008855:Microscopy, Electron, Scanning; D009995:Osmosis
chemical_list: D008840:Microfilament Proteins; C026615:villin
keywords: Ionocytes; Ionoregulation; Microvilli; Milkfish; Villin 1; Villin 1-like protein (VILL)