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

Abstract

BackgroundPeptide transporter 1 (PepT1, alias Slc15a1) mediates the uptake of dietary di/tripeptides in all vertebrates. However, in teleost fish, more than one PepT1-type transporter might function, due to specific whole genome duplication event(s) that occurred during their evolution leading to a more complex paralogue gene repertoire than in higher vertebrates (tetrapods).ResultsHere, we describe a novel di/tripeptide transporter in the zebrafish (Danio rerio), i.e., the zebrafish peptide transporter 1a (PepT1a; also known as Solute carrier family 15 member a1, Slc15a1a), which is a paralogue (78% similarity, 62% identity at the amino acid level) of the previously described zebrafish peptide transporter 1b (PepT1b, alias PepT1; also known as Solute carrier family 15 member 1b, Slc15a1b). Also, we report a basic analysis of the pept1a (slc15a1a) mRNA expression levels in zebrafish adult tissues/organs and embryonic/early larval developmental stages. As assessed by expression in Xenopus laevis oocytes and two-electrode voltage clamp measurements, zebrafish PepT1a, as PepT1b, is electrogenic, Na+-independent, and pH-dependent and functions as a low-affinity system, with K0.5 values for Gly-Gln at − 60 mV of 6.92 mmol/L at pH 7.6 and 0.24 mmol/L at pH 6.5 and at − 120 mV of 3.61 mmol/L at pH 7.6 and 0.45 mmol/L at pH 6.5. Zebrafish pept1a mRNA is highly expressed in the intestine and ovary of the adult fish, while its expression in early development undergoes a complex trend over time, with pept1a mRNA being detected 1 and 2 days post-fertilization (dpf), possibly due to its occurrence in the RNA maternal pool, decreasing at 3 dpf (~ 0.5-fold) and increasing above the 1–2 dpf levels at 4 to 7 dpf, with a peak (~ 7-fold) at 6 dpf.ConclusionsWe show that the zebrafish PepT1a-type transporter is functional and co-expressed with pept1b (slc15a1b) in the adult fish intestine. Its expression is also confirmed during the early phases of development when the yolk syncytial layer is present and yolk protein resorption processes are active. While completing the missing information on PepT1-type transporters function in the zebrafish, these results open to future investigations on the similar/differential role(s) of PepT1a/PepT1b in zebrafish and teleost fish physiology.

Growth Hormone Overexpression Induces Hyperphagia and Intestinal Morphophysiological Adaptations to Improve Nutrient Uptake in Zebrafish

“…Further, it was analyzed whether gh transgenesis could change the mRNA expression of genes related to transcellular transport of di and tripeptides in the intestine. According to Vacca et al (2019) , zebrafish PepT1a ( slc15a1a ) and PepT1b ( slc15a1b ) amino acid sequences shared 78% similarity and 62% identity. In this study, the levels of slc15a1a and slc15a1b transcripts were significantly increased ( p < 0.01 and 0.0001, respectively) in gh -transgenic fish compared to controls ( Figures 6C,D , respectively).…”

“… Verri et al (2003) described the molecular and functional characterization of the zebrafish PEPT1 transporter ( Verri et al, 2003 ). As in mammals, PEPT1 is abundantly expressed particularly in the proximal intestine and provides highly effective transport of small peptides across the brush-border membrane of enterocytes ( Verri et al, 2003 , 2017 ; Vacca et al, 2019 ). The expression levels and functional activities of peptide transporters are affected by various factors, such as dietary composition, nutrient supply, developmental stage, physiological status, and hormones ( Rubio-Aliaga and Daniel, 2008 ; Spanier, 2014 ; Spanier and Rohm, 2018 ), especially regarding the intestine.…”

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

“…The emerging slc15a1a paralog has just recently been identified, and therefore, limited information is still available for this gene. So far, only two studies on teleost species are found, i.e., in zebrafish ( Vacca et al, 2019 ) and in Atlantic salmon ( Gomes et al, 2020 ). Consequently, the largest part of the data available so far on teleost species about the functional role of Pept1 proteins refers to the Pept1b type ( Verri et al, 2010 ; Romano et al, 2014 ; Verri et al, 2017 ).…”

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

“…10 . Like other peptide transporters, such as mammalian and fish PepT1 (Renna et al ., 2011a; Vacca et al ., 2019) and rat PepT2 (Chen et al ., 1999), the τ / V curves of both PepT2 appeared bell-shaped ( Fig. 10 A and C ).…”

“…The Atlantic salmon represents the second teleost fish species (Ronnestad et al ., 2010; Gomes et al ., 2020) (this paper), after the zebrafish (Verri et al ., 2003; Romano et al ., 2006; Vacca et al ., 2019), for which both PepT1- and PepT2-type transporters have been functionally characterized. Due to a salmonid specific WGD, two functional PepT2-type transporters operate in the Atlantic salmon which seems to have resulted in a split of functions with respect to the canonical situation described in mammals, in which a single PepT2 transporter operates in the whole organism.…”