Background Aquatic species in several clades possess cement glands producing adhesive secretions of various strengths. In vertebrates, transient adhesive organs have been extensively studied in Xenopus laevis, other anurans, and in several fish species. However, the development of these structures is not fully understood. Results Here, we report on the development and functional morphology of the adhesive gland of a giant danio species, Devario malabaricus. We found that the gland is localized on the larval head, is composed of goblet‐like secretory cells framed by basal, bordering, and intercalated apical epithelial cells, and is innervated by the trigeminal ganglion. The gland allows nonswimming larvae to adhere to various substrates. Its secretory cells differentiate by 12 hours postfertilization and begin to disappear in the second week of life. Exogenous retinoic acid disrupts the gland's patterning. More importantly, the single mature gland emerges from fusion of two differentiated secretory cells fields; this fusion is dependent on nonmuscle myosin II function. Conclusions Taken together, our studies provide the first documentation of the embryonic development, structure, and function of the adhesive apparatus of a danioninae. To our knowledge, this is also the first report of a cement gland arising from convergence of two bilateral fields.

Cardiovascular diseases remain that number one cause of death in the northern hemisphere and are increasing globally in developing economies. In spite of evolutionary separation between fishes and mammalian, the use of non‐mammalian model species has significantly increased our understanding of cardiac diseases. We have recently described the growth and cardiovascular development of the Devario malabaricus, a giant danio (GD) species closely related to the zebrafish. We hypothesize that the adult GD heart can serve as a robust non‐mammalian model for in vivo studies of cardiac biology. Using immunostaining, transmission electron microscopy, scanning block‐face electron microscopy, and Doppler, we have characterized the anatomical and functional characteristics of the adult GD heart. First, we found that the adult giant danio possesses a thick and highly vascularized compact heart. Second, the GD heart possesses a junctional region populated with a fibroblasts network similar to that observed in zebrafish. Third, multiple large coronary vessels investing the compact myocardium are connected to and continuous with atrioventricular (AV) canal lumen. In addition, the AV canal and bulbus are highly innervated, suggesting complex regulation in heart function. Moreover, we demonstrate that their cardiac function can be measured using Doppler flow velocity. These studies along with previous findings support the GD as a robust model for the study of cardiac biology.Support or Funding Information1R15HD084262‐01, Buehler Family FoundationThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

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The factors necessary for the differentiation of cell types within the retina are incompletely understood. The transforming growth factor beta (TGF-β) superfamily, including TGF-β1 and 2, the bone morphogenetic proteins, and the activins have all been implicated in differentiation; however, the mechanisms by which these factors affect differentiation are only partially understood. The studies herein focus on a potential role for transforming growth factor β-activated kinase 1 (TAK1), a hub kinase that lies at the intersection of multiple signaling pathways, in the differentiation of cell types within the chick retina. Previous studies have focused predominantly on the role this kinase plays in the inflammation process and axonal growth. TAK1 is downstream of multiple signaling pathways that are critical to development of the central nervous system, including transforming growth factor β (TGFβ), bone morphogenetic proteins (BMPs), and activins. The present study indicates that activated TAK1 is found throughout the developing retina; however, it is localized at higher levels in dividing and differentiating cells. Further, ex ovo retinal studies using TAK1 inhibitor 5Z-7-oxozeaenol increased both progenitor and differentiating cell populations, accompanied by a substantial increase in proliferation and a smaller increase in cell death. These results indicate a unique role for TAK1 in differentiating and proliferating retinal cells.