Peptide Transporters in the Primary Gastrointestinal Tract of Pre-Feeding Mozambique Tilapia Larva

Abstract

Fish larvae differ greatly from the adult form in their morphology and organ functionality. The functionality of the gastrointestinal tract depends on the expression of various pumps, transporters, and channels responsible for feed digestion and nutrients absorption. During the larval period, the gastrointestinal tract develops from a simple closed tube, into its complex form with differentiated segments, crypts and villi, as found in the adult. In this study, we characterized the expression of three peptide transporters (PepT1a, PepT1b, and PepT2) in the gastrointestinal tract of Mozambique tilapia ( Oreochromis mossambicus ) larvae along 12 days of development, from pre-hatching to the completion of yolk sac absorption. Gene expression analysis revealed differential and complimentary time-dependent expression of the PepT1 variants and PepT2 along the larval development period. Immunofluorescence analysis showed differential protein localization of the three peptide transporters (PepTs) along the gastrointestinal tract, in a similar pattern to the adult. In addition, PepT1a was localized in mucosal cells in the larvae esophagus, in much higher abundance than in the adults. The results of this study demonstrate specialization of intestinal sections and absorbance potential of the enterocytes prior to the onset of active exogenous feeding, thus pointing to an uncharacterized function and role of the gastrointestinal tract and its transporters during the larval period.

Effects of Short-Term Fasting on mRNA Expression of Ghrelin and the Peptide Transporters PepT1 and 2 in Atlantic Salmon (Salmo salar)

“…In contrast, slc15a2a, compared to b-type paralog (but also compared to both slc15a1 types), shows a very low and constant mRNA expression levels along the GIT, suggesting a minor role in intestinal uptake of di-and tripeptides. Our data are in line with previous detections of slc15a2 in the intestine (Romano et al, 2006;Ostaszewska et al, 2018) and, in particular, in the distal intestinal segments, as reported in Nile tilapia (Huang et al, 2015), in juvenile turbot (Scophthalamus maximus) (Xu et al, 2016), and in Mozambique tilapia (Con et al, 2019), suggesting a downstream concerted integration of Pept2 with Pept1 in the functionality of gut physiology, in order to completely absorb di-and tripeptides from the intestinal lumen (Smith et al, 2013b;Bisesi et al, 2015). However, in contrast to zebrafish (Tian et al, 2015), 4 days of induced fasting did not seem to affect slc15a2 mRNA levels (for both types) in Atlantic salmon, except for a higher expression of the fasted group in AMG for slc15a2b, and this difference might be due to different teleost species studied (Cypriniformes vs. Salmoniformes family representatives).…”

“…In our analysis, the effects of fasting on the gene expression variation were not evaluated in the complete GIT but, rather, in specific gut compartments and thus identifying PC and MG as the most responsive compartments to fasting. Furthermore, for the first time in Atlantic salmon, slc15a1a is shown to respond to fasting with lowering mRNA expression levels, confirming the high flexibility of both transporters in the context of gut physiology and their ability to respond to different luminal conditions and signals, as previously shown in Mozambique tilapia (Con et al, 2019), in Nile tilapia (Hallali et al, 2018), and in European sea bass (Kokou et al, 2019). Based on correlation analysis, moreover, the slc15a1 expression in PC and AMG appeared to be associated with the residual digesta content of the MG, suggesting high sensitivity of the peptide transporter to external stimuli.…”

The peptide transporter 1a of the zebrafish Danio rerio, an emerging model in nutrigenomics and nutrition research: molecular characterization, functional properties, and expression analysis

“…In fact, at least to our knowledge, the only study available in the literature that specifically compares pept1a ( scl15a1a ) and pept1b ( slc15a1b ) in pre-feeding stages larvae refers to the Mozambique tilapia ( Oreochromis mossambicus ) and is limited to the intestinal organ only. In this case, pept1a ( slc15a1a ) and pept1b ( slc15a1b ) temporal trend of expression in the intestine goes parallel from 3 to 14 dpf (for details, see Table 4, and literature therein [49]).…”

Functional characterization of Atlantic salmon (Salmo salar L.) PepT2 transporters

“…In contrast, in the Atlantic salmon, the slc15a2a paralogue exhibits a widespread tissue distribution, in terms of the presence of mRNA, but it is most abundant in the brain and, notably, in the gills. The expression of a PepT2 in the brain, operating as a di/tripeptide uptake system, has been observed in mammals (Wada et al ., 2005; Biegel et al ., 2006; Kamal et al ., 2008; Keep & Smith, 2011; Smith et al ., 2013; Viennois et al ., 2018) as well as in teleost fish species, e.g., zebrafish (Romano et al ., 2006) and Mozambique tilapia (Con et al ., 2019). But, noteworthy, the identification of PepT2 mRNA transcripts in the gills opens to the hypothesis that a di/tripeptide transporter might also be operating in such an epithelial tissue moving di/tripeptides directly from the aquatic environment to the blood and/or vice versa.…”

“…Larva (3-14 dpf) NA (Con et al, 2017;Chourasia et al, 2018;Con et al, 2019;Con et al, 2021) Adult Proximal, mid and distal intestine, kidney, muscle, liver, brain, pituitary, skin, stomach, spleen, heart, fat, gills, oesophagus…”