RESUMO
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.
RESUMO
During embryogenesis, the body axis elongates and specializes. In vertebrate groups such as salamanders and lizards, elongation of the posterior body axis (tail) continues throughout life. This phenomenon of post-embryonic tail elongation via addition of vertebrae has remained largely unexplored, and little is known about the underlying developmental mechanisms that promote vertebral addition. Our research investigated tail elongation across life stages in a non-model salamander species, Eurycea cirrigera (Plethodontidae). Post-embryonic addition of segments suggests that the tail tip retains some aspects of embryonic cell/tissue organization and gene expression throughout the life cycle. We describe cell and tissue differentiation and segmentation of the posterior tail using serial histology and expression of the axial tissue markers, MF-20 and Pax6. Embryonic expression patterns of HoxA13 and C13 are shown with in situ hybridization. Tissue sections reveal that the posterior spinal cord forms via cavitation and precedes development of the underlying cartilaginous rod after embryogenesis. Post-embryonic tail elongation occurs in the absence of somites and mesenchymal cells lateral to the midline express MF-20. Pax6 expression was observed only in the spinal cord and some mesenchymal cells of adult Eurycea tails. Distinct temporal and spatial patterns of posterior Hox13 gene expression were observed throughout embryogenesis. Overall, important insights to cell organization, differentiation, and posterior Hox gene expression may be gained from this work. We suggest that further work on gene expression in the elongating adult tail could shed light on mechanisms that link continual axial elongation with regeneration.
