Chromaffin cells in the adrenal homolog of Aphanius fasciatus (teleost fish) express piecemeal degranulation in response to osmotic stress: A hint for a conservative evolutionary process

Abstract

The effect of severe osmotic stress on the ultrastructural morphology of chromaffin cells in the adrenal homolog of Aphanius fasciatus, a small eurhyaline teleost living in saltpans, was evaluated by electron microscopy quantitative analysis. Fishes were transferred from salt water, whose salinity was 3.7%, to dechlorinated tap water and chromaffin cells were studied at resting condition and after 2 and 48 hr from the beginning of the experiment. Ultrastructural examination revealed a series of granule and cytoplasmic changes highly specific for piecemeal degranulation (PMD), a secretory process based on vesicular transport of cargoes from within granules for extracellular release, which was previously described in chromaffin cells of the mouse, rat, and human adrenal medulla. There was indeed a significant trend toward loss of content material from chromaffin granules accompanied by enlargement of granule size. Remarkably, chromaffin granules maintained their individual close structure during the whole releasing process and eventually transformed into large empty containers. A dramatic increase in the density of small, membrane-bound, variably electron-dense vesicles free in the cytoplasm or attached to granules was recognized during the first 2 hr of stress response. These features fell to control levels after 48 hr. A similar timecourse pattern was observed concerning the formation of budding projections from the surface of chromaffin granules. This study provides new insight into PMD physiology and suggests that PMD is part of an adaptive secretory response to severe osmotic stress in fishes. From an evolutionary point of view, this study lends support to the concept that PMD is a secretory mechanism highly conserved throughout vertebrate classes.

Suggestive evidence of a vesicle‐mediated mode of cell degranulation in chromaffin cells. A high‐resolution scanning electron microscopy investigation

“…This study provides high‐resolution scanning images of rat adrenal chromaffin cells. Some of these 3D ultrastructures were previously investigated with conventional TEM and regarded as highly suggestive of PMD in chromaffin cells (Crivellato et al. 2003, 2004, 2005, 2006, 2009a,b).…”

“…Ultrastructural criteria for detecting PMD by means of electron microscopy include specific granular and cytoplasmic changes. Both kinds are recognizable in chromaffin cells (Crivellato et al. 2003, 2004, 2005, 2006, 2009a,b).…”

“…In chromaffin cells, this suggestive degranulation pathway may represent a versatile model of cell secretion. On the one hand, it may be part of a generalized secretory reaction to acute adverse conditions, as during exposure to severe osmotic stress in fish (Crivellato et al. 2006).…”

“…As a result, PMD would accomplish discharge of secretory constituents from storage granules without granule-to-granule and granule-to-plasma membrane fusion events and without direct granule opening to the cell exterior. It is of note that ultrastructural clues diagnostic of PMD have been identified with transmission electron microscopy (TEM) in chromaffin cells from different species including man, mouse, rat, chicken embryo, newt and fish (Crivellato et al 2003(Crivellato et al , 2004(Crivellato et al , 2005(Crivellato et al , 2006(Crivellato et al , 2009a. In chromaffin cells, this suggestive degranulation pathway may represent a versatile model of cell secretion.…”

Distribution of natural populations of the killifishAphanius fasciatus(Valenciennes, 1821) (Teleostei: Cyprinodontidae) in Italy: past and current status, and future trends

“…Populations of A. fasciatus are interesting models for the study of morphological polymorphism (Kiener & Schachter 1974;Tigano & Ferrito 1984), genetic diversity (Maltagliati 1998a(Maltagliati , 1998b(Maltagliati , 1999Ferrito et al 2007;Triantafyllidis et al 2007;Pappalardo et al 2008), relationships between phenotype and genotype (Ferrito et al 2003;Maltagliati et al 2003), macroevolutionary processes (Villwock 1982;Hrbek & Meyer 2003), evolution of physiological adaptations (Crivellato et al 2006), reproductive behaviour and sexual selection (Malavasi et al 2010;Cavraro et al 2013aCavraro et al , 2013b and can be also employed as effective "sentinels" to detect genotoxic pollutants in coastal lagoon ecosystems (Mosesso et al 2012).…”