Morphology and glandular composition of the myzorhynchus and the remnant apical organ in adult cestodes of the order Rhinebothriidea from batoids off Argentina.

The main objective of this study was to analyze the function of the myzorhynchus and remnant apical organ of adult cestodes in the order Rhinebothriidea. Several features of these structures were analyzed in 12 species belonging to six genera and two families. In particular, the glandular composition of the myzorhynchus of four species from Echeneibothriidae (i.e., Notomegarhynchus navonae and three species of Echeneibothrium) was studied using histochemical techniques and/or transmission electron microscopy. In addition, the presence of a remnant apical organ and its glandular composition were analized in six species of Rhinebothriidae and in two species of Semiorbiseptum, whose familial assignment is uncertain. We also evaluated the importance of these characters for diagnosis. The same type of gland cell was found in the myzorhynchus of Echeneibothrium species and in the remnant apical organ of Semiorbiseptum species. These gland cells were Coomassie brilliant blue-positive, periodic acid Schiff-positive and Alcian blue-negative, consistent with a glycoprotein secretion possibly involved in adhesion to the host mucosa and proteolysis. The type of gland cells found in the myzorhynchus of N. navonae were Coomassie brilliant blue-negative, periodic acid Schiff-positive and Alcian blue-positive, consistent with the production of adhesive and protective substances. The type of gland cells in the myzorhynchus and in the remnant apical organ could be a useful character for the generic diagnosis of Echeneibothrium and Semiorbiseptum, respectively. A remnant apical organ was only found in Semiorbiseptum, with its presence/absence being important as a diagnostic character at the generic level for Semiorbiseptum, Scalithrium, and Rhinebothroides. A secondary objective was to characterize the microthrix pattern of the myzorhynchus of N. navonae. An extended distribution of spinitriches was detected, which may allow a better adhesion of this large species to the host mucosa, as the main function of spinitriches is presumably that of adhesion.

Injury-induced purinergic signalling molecules upregulate pluripotency gene expression and mitotic activity of progenitor cells in the zebrafish retina.

Damage in fish activates retina repair that restores sight. The purinergic signalling system serves multiple homeostatic functions and has been implicated in cell cycle control of progenitor cells in the developing retina. We examined whether changes in the expression of purinergic molecules were instrumental in the proliferative phase after injury of adult zebrafish retinas with ouabain. P2RY1 messenger RNA (mRNA) increased early after injury and showed maximal levels at the time of peak progenitor cell proliferation. Extracellular nucleotides, mainly ADP, regulate P2RY1 transcriptional and protein expression. The injury-induced upregulation of P2RY1 is mediated by an autoregulated mechanism. After injury, the transcriptional expression of ecto-nucleotidases and ecto-ATPases also increased and ecto-ATPase activity inhibitors decreased Müller glia-derived progenitor cell amplification. Inhibition of P2RY1 endogenous activation prevented progenitor cell proliferation at two intervals after injury: one in which progenitor Müller glia mitotically activates and the second one in which Müller glia-derived progenitor cells amplify. ADPßS induced the expression of lin28a and ascl1a genes in mature regions of uninjured retinas. The expression of these genes, which regulate multipotent Müller glia reprogramming, was significantly inhibited by blocking the endogenous activation of P2RY1 early after injury. We consistently observed that the number of glial fibrillary acidic protein-BrdU-positive Müller cells after injury was larger in the absence than in the presence of the P2RY1 antagonist. Ecto-ATPase activity inhibitors or P2RY1-specific antagonists did not modify apoptotic cell death at the time of peak progenitor cell proliferation. The results suggested that ouabain injury upregulates specific purinergic signals which stimulates multipotent progenitor cell response.

Extracellular ADP regulates lesion-induced in vivo cell proliferation and death in the zebrafish retina.

Regeneration and growth that occur in the adult teleost retina by neurogenesis have been helpful in identifying molecular and cellular mechanisms underlying cell proliferation and differentiation. In this report, we demonstrate that endogenous purinergic signals regulate cell proliferation induced by a cytotoxic injury of the adult zebrafish retina which mainly damages inner retinal layers. Particularly, we found that ADP but not ATP or adenosine significantly enhanced cell division as assessed by 5-bromo-2'-deoxyuridine incorporation following injury, during the degenerative and proliferative phase of the regeneration process. This effect of ADP occurs via P2Y1 metabotropic receptors as shown by intra-ocular injection of selective antagonists. Additionally, we describe a role for purinergic signals in regulating cell death induced by injury. Scavenging of extracellular nucleotides significantly increased cell death principally seen in the inner retinal layers. This effect is partially reproduced by blocking P2Y1 receptors suggesting a neuroprotective function for ADP, which is derived from extracellular ATP probably released by dying cells as a consequence of the ouabain treatment. This study demonstrates a crucial role for ADP as a paracrine signal in the repair of retinal tissue following injury.