Giant danios (genus Devario), like zebrafish, are teleosts belonging to the danioninae subfamily of cyprinids. Adult giant danios are used in a variety of investigations aimed at understanding cellular and physiological processes, including heart regeneration. Despite their importance, little is known about development and growth in giant danios, or their cardiac and coronary vessels development. To address this scarcity of knowledge, we performed a systematic study of a giant danio (Devario malabaricus), focusing on its cardiac development, from the segmentation period to ten months post-fertilization. Using light and scanning electron microscopy, we documented that its cardiovascular development and maturation proceed along well defined dynamic and conserved morphogenic patterns. The overall size and cardiovascular expansion of this species was significantly impacted by environmental parameters such as rearing densities. The coronary vasculature began to emerge in the late larval stage. More importantly, we documented two possible loci of initiation of the coronary vasculature in this species, and compared the emergence of the coronaries to that of zebrafish and gourami. This is the first comprehensive study of the cardiac growth in a Devario species, and our findings serve as an important reference for further investigations of cardiac biology using this species.

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.

Doxorubicin (Dox), an antineoplastic anthracycline used in the treatment of childhood leukemia, is associated with late‐onset cardiomyopathy. The mechanisms of Dox‐induced cardiac dysfunction are an area of intense investigations. Using light and transmission electron microscopy (TEM), we studied the effects of Dox on the heart of giant danio (GD), a small fish closely related to zebrafish. We compared short‐term high‐dose to long‐term low‐dose effects of Dox administrations. We found that short‐term (4 days) high‐dose Dox induced little inflammation or collagen accumulation in the GD myocardium. By contrast long‐term (4 weeks) low‐dose Dox induced apoptosis (TUNEL, TEM) and inflammation (MPO, TEM) in the ventricular myocardium. The number of MPO‐positive cells increased by 2 folds and 4 folds in Dox‐treated hearts, at 1 and 4 weeks respectively, with cell cycle activity (Edu) in cardiac myocytes (CM) and increased fibrosis (Trichrome, TEM). Interestingly, we found a spatially‐restricted pattern of fibrosis in the compact heart (CH). Consistent with this finding we observed by TEM that activated fibroblasts in the CH contributed to collagen accumulation. This data suggests that, except for marked cell cycle activation in CM, the GD heart response to Dox treatment appears analogous to that of human. Thus the GD may serve as an important model for the study of Dox‐induced cardiomyopathy.Grant Funding Source: FDC

Cement glands are transient ectodermally‐derived adhesive organs found in the larval stage of several aquatic species. We have identified a transient structure on the apical aspect of a giant danio (Devario cf. malabaricus) head, a member of the danioninae subfamily of cyprinids. We hypothesize that this structure is a cement gland (CG), the primary adhesive organ of the giant danio (GD), and that its cellular components support its function. Using a novel adhesion assay, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and serial block face‐scanning electron microscopy (SBF‐SEM), we investigated the function of the CG and the structures of the cells that constitute it. Our studies have shown that the gland produces a glycoconjugates‐containing mucus that allows larvae to attach to surfaces in their environments. The larvae remain attached until day 5 when they begin swimming. Lectin staining and SEM revealed that the CG is composed primarily of goblet and epithelial cells organized in a lattice‐like pattern. These studies also show that the CG disappears by week 2. TEM confirms that the CG consists of elongated goblet cells containing granules of varying electron densities. These cells are framed apically by intercalated epithelial cells, and basally by a layer of squamous epithelium. Finally, we used SBF‐SEM and Amira 6 to reconstruct the three dimensional spatial relationship of these cells. To our knowledge, this is the first functional and ultrastructural study of a CG in a danioninae. Our results suggest that the cement gland is an important organ in GD development.Support or Funding InformationDePauw FDC, SRF, Faculty FellowshipThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.