Structural differentiation of apical openings in active mitochondria-rich cells during early life stages of Nile tilapia
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Structural differentiation of apical openings in active mitochondria-rich cells during early life stages of Nile tilapia (Oreochromis niloticus L.) as a response to osmotic challenge S. Fridman • K. J. Rana • J. E. Bron
Received: 19 July 2012 / Accepted: 31 December 2012 / Published online: 11 January 2013 Ó Springer Science+Business Media Dordrecht 2013
Abstract This study examines the structural differentiation of the apical crypts of mitochondria-rich cells (MRCs) in Nile tilapia as a response to osmotic challenge. Larvae were transferred from freshwater at 3 days posthatch to 12.5 and 20 ppt and were sampled at 24- and 48-h post-transfer. Scanning electron microscopy allowed quantification of MRCs, based on apical crypt appearance and surface area, resulting in a morphological classification of ‘sub-types’, that is, Type I or absorptive (surface area range 5.2–19.6 lm2), Type II or active absorptive form (surface area range 1.1–15.7 lm2), Type III or weakly functioning form (surface area range 0.08–4.6 lm2) and Type IV or active secreting form (surface area range 4.1–11.7lm2). Mucus cell crypts were discriminated from those of MRCs based on the presence of globular extensions and quantified. Density and frequency of MRCs and mucus cells varied significantly according to the experimental salinity and time post-transfer; in S. Fridman K. J. Rana J. E. Bron Institute of Aquaculture, University of Stirling, Stirling FK9 3LA, Scotland, UK S. Fridman (&) French Associates Institute for Agriculture and Biotechnology of Drylands, Blaustein Institute for Desert Research, Ben Gurion University, Sede-Boqer Campus, 84990 Beersheba, Israel e-mail: [email protected] K. J. Rana Aquaculture Division, University of Stellenbosch, Stellenbosch 7602, South Africa
freshwater-adapted larvae, all types were present except Type IV but, following transfer to elevated salinities, Type I and Type II disappeared and appeared to be replaced by Type IV crypts. Type III crypt density remained constant following transfer. Transmission electron microscopy with immunogold labelling, using a novel pre-fixation technique with anti-Na?/K?-ATPase, allowed complementary ultrastructural visualisation of specific localisation of the antibodies on active MRCs, permitting a review of MRC apical morphology and related Na?/K?-ATPase binding sites. Keywords Mitochondria-rich cells Osmoregulation Cellular differentiation Nile tilapia Ontogeny
Introduction In an aquatic environment, an organism that is noniso-osmotic to its environment will experience passive diffusional movements of solutes and water between the environment and the extra-cellular fluids. As opposed to movement of gases, specific compensatory ion movements require specific carriers, and this ‘metabolic machinery’ (Rombough 2004) is found in a specific cell type, that is, the mitochondria-rich cell (MRC). Numerous studies, dedicated to the study of their form and function, have established that these cells are the primary extra-renal site responsible for the transepithelia
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