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Figure 1 | Frontiers in Zoology

Figure 1

From: The role of osmotic stress transcription factor 1 in fishes

Figure 1

Proposed model of Ostf1 in fishes. The model combines all the findings from various fishes. Different colors represent different fishes (green for eel, red for medaka, brown for Mozambique tilapia, orange for Nile tilapia, and blue for zebrafish). It should be noted that the model might not be fitted for all fishes; however, it suggests the general signaling flow of Ostf1 in fishes from its regulators to downstream functions. Different molecules or stressors could regulate the expression of Ostf1. Hyperosmotic stress is one such stressor. In medaka, osmotic stress activates the SEK/JNK pathway to stimulate Ostf1b [21]. In addition, cortisol injection into Mozambique tilapia stimulates the expression of Ostf1 [11]. In an eel gill cell culture model, DEX was shown to induce Ostf1 via the Akt-GSK3β pathway [20]. Furthermore, eel gill immunohistochemical staining has shown the activation of p-ERK and Ostf1 after fresh water to seawater transfer. p-ERK and Ostf1 co-expressed at the same time and further experiments are required in order to determine whether pERK stimulates Ostf1, or vice versa [18]. The final regulator in this model is miR429 in Nile tilapia. Similar to other miRNAs, miR429 may inhibit the expression of ostf1 mRNA [12]. The induction of Ostf1 leads to different downstream functions. In euryhaline fresh water medaka, Ostf1b may further activate the ROCK pathway for cytoskeleton reorganization, and cell migration [22]. Furthermore, at the same time, it may directly stimulate the mRNA expression of different ion transporters or channels to maintain water and ion homeostasis [21]. These osmoregulatory processes have been shown to be related to the Ostf1b. In the stenohaline zebrafish, Ostf1 functions as a ventralizing gene that plays critical dorsal-ventral roles during early embryogenesis [26]. To summarize, Ostf1 has different functions in fishes, ranging from regulating osmotic responses (osmoregulation) to playing critical roles in early development (embryogenesis).

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