TGFβ (transforming growth factor β) and keratocyte motility in 24 h zebrafish explant cultures

Fish keratocytes are used as a model system for the study of the mechanics of cell motility because of their characteristic rapid, smooth gliding motion, but little work has been done on the regulation of fish keratocyte movement. As TGFβ (transforming growth factor β) plays multiple roles in primary human keratinocyte cell migration, we investigated the possible involvement of TGFβ in fish keratocyte migration. Studying the involvement of TGFβ1 in 24 h keratocyte explant allows the examination of the cells before alterations in cellular physiology occur due to extended culture times. During this initial period, TGFβ levels increase 6.2-fold in SFM (serum-free medium) and 2.4-fold in SFM+2% FBS (fetal bovine serum), while TGFβ1 and TGFβRII (TGFβ receptor II) mRNA levels increase ∼3- and ∼5-fold respectively in each culture condition. Two measures of motility, cell sheet area and migration distance, vary with the amount of exogenous TGFβ1 and culture media. The addition of 100 ng/ml exogenous TGFβ1 in SFM increases both measures [3.3-fold (P = 4.5×10-5) and 26% (P = 2.1×10-2) respectively]. In contrast, 100 ng/ml of exogenous TGFβ1 in medium containing 2% FBS decreases migration distance by 2.1-fold (P = 1.7×10-7), but does not affect sheet area. TGFβ1 (10 ng/ml) has little effect on cell sheet area in SFM cultures, but leads to a 1.8-fold increase (P = 1.5×10-2) with 2% FBS. The variable response to TGFβ1 may be, at least in part, explained by the effect of 2% FBS on cell morphology, mode of motility and expression of endogenous TGFβ1 and TGFβRII. Together, these results suggest that expression of TGFβ and its receptor are up-regulated during zebrafish keratocyte explant culture and that TGFβ promotes fish keratocyte migration.