Abstract
Unpaired fins, which are the most ancient form of locomotory appendages in chordates, had emerged at least 500 million years ago. While it has been suggested that unpaired fins and paired fins share structural similarities, cellular and molecular mechanisms that regulate the outgrowth of the former have not been fully elucidated yet. Using the ventral fin fold in zebrafish as a model, here, we investigate how the outgrowth of the unpaired fin is modulated. We show that Bone Morphogenetic Protein (BMP) signaling restricts extension of the ventral fin fold along the proximodistal axis by modulating diverse aspects of cellular behaviors. We find that lack of BMP signaling, either caused by genetic or chemical manipulation, prolongs the proliferative capacity of epithelial cells and substantially increases the number of cells within the ventral fin fold. In addition, inhibition of BMP signaling attenuates the innate propensity of cell division along the anteroposterior axis and shifts the orientation of cell division toward the proximodistal axis. Moreover, abrogating BMP signaling appears to induce excessive distal migration of cells within the ventral fin fold, and therefore precipitates extension along the proximodistal axis. Taken together, our data suggest that BMP signaling restricts the outgrowth of the ventral fin fold during zebrafish development.
Highlights
Teleosts are a paraphyletic group composed of diverse species, with characteristic anatomical features that enable living in aquatic environments
We investigated the role of Bone morphogenetic protein (Bmp) signaling on the morphogenesis of unpaired fin, using ventral fin fold in zebrafish embryo as a model
We postulated that unpaired fins may respond differently to Bmp signaling as shown in paired fins
Summary
Teleosts are a paraphyletic group composed of diverse species, with characteristic anatomical features that enable living in aquatic environments. Fins, which are the major form of appendages, are arguably the most anatomically distinct features of teleosts Based on their morphology and number, fins could be divided into two types, unpaired fins and paired fins (Freitas et al, 2014; Larouche et al, 2017). Recent phylogenetic analyses indicate that unpaired fins are more ancient structures, evolved in ostracoderms approximately 100 million years earlier than the advent of paired fins (Coates, 1995; Shubin, 1995) These two types of fins may have emerged by separate evolutionary events (Coates, 1995; Grandel and Schulte-Merker, 1998, van den Boogaart et al, 2012). Paired fins are connected to the body by girdles which allow articulation, while unpaired fins are extended directly from the body wall as a result of mesenchymal expansion within embryonic fin folds (Grandel and Schulte-Merker, 1998; Yamanoue et al, 2010)
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