Equarin is involved as an FGF signaling modulator in chick lens differentiation

Abstract

Lens growth involves the proliferation of epithelial cells, followed by their migration to the equator region and differentiation into secondary fiber cells. It is widely accepted that fibroblast growth factor (FGF) signaling is required for the differentiation of lens epithelial cells into crystallin-rich fibers, but this signaling is insufficient to induce full differentiation. To better understand lens development, investigatory and functional analyses of novel molecules are required. Here, we demonstrate that Equarin, which is a novel secreted molecule, was expressed exclusively in the lens equator region during chick lens development. Equarin upregulated the expression of fiber markers, as demonstrated using in ovo electroporation. In a primary lens cell culture, Equarin promoted the biochemical and morphological changes associated with the differentiation of lens epithelial cells to fibers. A loss-of-function analysis was performed using zinc-finger nucleases targeting the Equarin gene. Lens cell differentiation was markedly inhibited when endogenous Equarin was blocked, indicating that Equarin was essential for normal chick lens differentiation. Furthermore, biochemical analysis showed that Equarin directly bound to FGFs and heparan sulfate proteoglycan and thereby upregulated the expression of phospho-ERK1/2 (ERK-P) proteins, the downstream of the FGF signaling pathway, in vivo and in vitro. Conversely, the absence of endogenous Equarin clearly diminished FGF-induced fiber differentiation. Taken together, our results suggest that Equarin is involved as an FGF modulator in chick lens differentiation.

Equarin is involved in cell adhesion by means of heparan sulfate proteoglycan during lens development

“…This concept is further suggested by the binding of Equarin to heparin Sepharose (Song et al, 2012).…”

“…Immunostaining was performed using specific primary antibodies, followed by incubation with fluorescent secondary antibodies and Hoechst 33342 staining to label the nuclei. The following primary antibodies were used for immunostaining: anti-Equarin monoclonal antibody (Song et al, 2012) …”

“…Previously, we identified Equarin as a novel lens differentiation inducer through fibroblast growth factor (FGF) signaling (Song et al, 2012). Mouse CCDC80 (coiled-coil domain-containing protein 80; also known as DRO1 and URB), which is highly homologous and structurally similar to chick Equarin, is involved in cell adhesion and migration (Manabe et al, 2008).…”

DRO1/CCDC80: a Novel Tumor Suppressor of Colorectal Carcinogenesis

“…A different effect on MAP/ERK signaling by the Dro1/ Ccdc80 chicken homologue Equarin has been observed during lens cell differentiation [13]. In lens cells, overexpression of Dro1/Ccdc80, both in vitro and in vivo, results in increased p-ERK1/2 levels.…”

“…Dro1/Ccdc80 has been shown to be involved in colon carcinogenesis [3••, 4] and has also been implicated in thyroid, mammary, and ovarian tumorigenesis [5••, 6-9]. Moreover, DRO1/CCDC80 has been shown to play a significant role in cell differentiation during adipogenesis [10] and lens development [11][12][13][14] (reviewed in [15•]), to inhibit steroidogenesis in adrenocortical cells [16], and to be important for neural development of the zebrafish [17]. This article is part of the Topical Collection on Molecular Biology * Jessica I.…”