Abstract
We previously showed that, according to the frequency and distribution of specific cell types, the rainbow trout (RT) intestinal mucosa can be divided in two regions that form a complex nonlinear three-dimensional (3D) pattern and have a different renewal rate. This work had two aims. First, we investigated whether the unusual distribution of cell populations reflects a similar distribution of functional activities. To this end, we determined the protein expression pattern of three well-defined enterocytes functional markers: peptide transporter 1 (PepT1), sodium–glucose/galactose transporter 1 (SGLT-1), and fatty-acid-binding protein 2 (Fabp2). Second, we characterized the structure of RT intestinal stem-cell (ISC) niche and determined whether the different proliferative is accompanied by a different organization and/or extension of the stem-cell population. We studied the expression and localization of well-characterized mammal ISC markers: LGR5, HOPX, SOX9, NOTCH1, DLL1, and WNT3A. Our results indicate that morphological similarity is associated with similar function only between the first portion of the mid-intestine and the apical part of the complex folds in the second portion. Mammal ISC markers are all expressed in RT, but their localization is completely different, suggesting also substantial functional differences. Lastly, higher renewal rates are supported by a more abundant ISC population.
Highlights
Due to its high nutritional value, global fish consumption has constantly grown in the past few decades, reaching all-time records
A preliminary morphological analysis did not evidence morphological alterations such as proximal intestine vacuolization, nuclear positioning disparity, fold shortening, or fold branching, confirming the animals’ healthy state. It confirmed that goblet cells were numerous, swollen, and actively secreting in the first segment of the mid-intestine and in the apical portion of the complex folds of the second segment, whereas they were scarce and inactive in the pyloric caeca and in the rest of the second segment of the mid-intestine
The presence of the peptide transporter 1 (PepT1) symporter was highest in the brush border of pyloric caeca enterocytes, was moderate in the first segment of the mid-intestine (Figure 2) and in the apical part of the complex folds of the second segment, and was completely absent in the rest of the second segment of the mid-intestine mucosa (Figure 3)
Summary
Due to its high nutritional value, global fish consumption has constantly grown in the past few decades, reaching all-time records. Following the nomenclature proposed by Bjørgen et al [7] for the Atlantic salmon (Salmo salar), along the craniocaudal axis of the intestine, we first meet the pyloric caeca, over 50 hollow tubes that branch off the first segment of the mid-intestine, to increase its absorptive surface. Throughout the length of the whole intestine, the mucosa raises in large folds, and, in the second segment, some of them are up to three times higher with smaller secondary folds branching out along their length. For their peculiar structure, these are known as complex folds [5,9]
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