Proline Dehydrogenase (PRODH) Is Expressed in Lung Adenocarcinoma and Modulates Cell Survival and 3D Growth by Inducing Cellular Senescence.

The identification of markers for early diagnosis, prognosis, and improvement of therapeutic options represents an unmet clinical need to increase survival in Non-Small Cell Lung Cancer (NSCLC), a neoplasm still characterized by very high incidence and mortality. Here, we investigated whether proline dehydrogenase (PRODH), a mitochondrial flavoenzyme catalyzing the key step in proline degradation, played a role in NSCLC tumorigenesis. PRODH expression was investigated by immunohistochemistry; digital PCR, quantitative PCR, immunoblotting, measurement of reactive oxygen species (ROS), and functional cellular assays were carried out. PRODH expression was found in the majority of lung adenocarcinomas (ADCs). Patients with PRODH-positive tumors had better cancer-free specific and overall survival compared to those with negative tumors. Ectopic modulation of PRODH expression in NCI-H1299 and the other tested lung ADC cell lines decreased cell survival. Moreover, cell proliferation curves showed delayed growth in NCI-H1299, Calu-6 and A549 cell lines when PRODH-expressing clones were compared to control clones. The 3D growth in soft agar was also impaired in the presence of PRODH. PRODH increased reactive oxygen species production and induced cellular senescence in the NCI-H1299 cell line. This study supports a role of PRODH in decreasing survival and growth of lung ADC cells by inducing cellular senescence.

The Lepidopteran KAAT1 and CAATCH1: Orthologs to Understand Structure-Function Relationships in Mammalian SLC6 Transporters.

To the SLC6 family belong 20 human transporters that utilize the sodium electrochemical gradient to move biogenic amines, osmolytes, amino acids and related compounds into cells. They are classified into two functional groups, the Neurotransmitter transporters (NTT) and Nutrient amino acid transporters (NAT). Here we summarize how since their first cloning in 1998, the insect (Lepidopteran) Orthologs of the SLC6 family transporters have represented very important tools for investigating functional-structural relationships, mechanism of transport, ion and pH dependence and substate interaction of the mammalian (and human) counterparts.

TRPV4 and TRPM8 as putative targets for chronic low back pain alleviation.

The purpose of this study is to investigate the presence of nervous fibers and expression of TRP channels in samples harvested during decompressive/fusion spine surgeries from patients affected by chronic low back pain (CLBP). The aim was to understand if members of this family of receptors played a role in detection and processing of painful stimuli, to eventually define them as potential targets for CLBP alleviation. Expression of transient receptor potential (TRP) channels (A1, V1, V2, V4, and M8) was evaluated in samples from different periarticular sites of 6 patients affected by CLBP, at both protein and transcript levels. The capsular connective pathological tissue appeared infiltrated by sensitive unmyelinated nervous fibers. An increase in TRP channel mRNAs and proteins was observed in the pathological capsule compared with tissues collected from the non-symptomatic area in five of the six analyzed patients, independently by the location and number of affected sites. In particular, TRPV4 and TRPM8 were consistently upregulated in pathological tissues. Interestingly, the only patient showing a different pattern of expression also had a different clinical history. TRPV4 and TRPM8 channels may play a role in CLBP and warrant further investigations as possible therapeutic targets.

Identification and characterization of the Atlantic salmon peptide transporter 1a.

Peptide transporter 1 (PepT1) mediates the uptake of dietary di-/tripeptides in vertebrates. However, in teleost fish gut, more than one PepT1-type transporter might operate, because of teleost-specific whole gen(om)e duplication event(s) that occurred during evolution. Here, we describe a novel teleost di-/tripeptide transporter, i.e., the Atlantic salmon (Salmo salar) peptide transporter 1a [PepT1a; or solute carrier family 15 member 1a (Slc15a1a)], which is a paralog (77% similarity and 64% identity at the amino acid level) of the well-described Atlantic salmon peptide transporter 1b [PepT1b, alias PepT1; or solute carrier family 15 member 1b (Slc15a1b)]. Comparative analysis and evolutionary relationships of gene/protein sequences were conducted after ad hoc database mining. Tissue mRNA expression analysis was performed by quantitative real-time PCR, whereas transport function analysis was accomplished by heterologous expression in Xenopus laevis oocytes and two-electrode voltage-clamp measurements. Atlantic salmon pept1a is highly expressed in the proximal intestine (pyloric ceca ≈ anterior midgut > midgut >> posterior midgut), in the same gut regions as pept1b but notably ~5-fold less abundant. Like PepT1b, Atlantic salmon PepT1a is a low-affinity/high-capacity system. Functional analysis showed electrogenic, Na+-independent/pH-dependent transport and apparent substrate affinity (K0.5) values for Gly-Gln of 1.593 mmol/L at pH 7.6 and 0.076 mmol/L at pH 6.5. In summary, we show that a piscine PepT1a-type transporter is functional. Defining the role of Atlantic salmon PepT1a in the gut will help to understand the evolutionary and functional relationships among peptide transporters. Its functional characterization will contribute to elucidate the relevance of peptide transporters in Atlantic salmon nutritional physiology.

Dictyostelium Nramp1, which is structurally and functionally similar to mammalian DMT1 transporter, mediates phagosomal iron efflux.

The Nramp (Slc11) protein family is widespread in bacteria and eukaryotes, and mediates transport of divalent metals across cellular membranes. The social amoeba Dictyostelium discoideum has two Nramp proteins. Nramp1, like its mammalian ortholog (SLC11A1), is recruited to phagosomal and macropinosomal membranes, and confers resistance to pathogenic bacteria. Nramp2 is located exclusively in the contractile vacuole membrane and controls, synergistically with Nramp1, iron homeostasis. It has long been debated whether mammalian Nramp1 mediates iron import or export from phagosomes. By selectively loading the iron-chelating fluorochrome calcein in macropinosomes, we show that Dictyostelium Nramp1 mediates iron efflux from macropinosomes in vivo. To gain insight in ion selectivity and the transport mechanism, the proteins were expressed in Xenopus oocytes. Using a novel assay with calcein, and electrophysiological and radiochemical assays, we show that Nramp1, similar to rat DMT1 (also known as SLC11A2), transports Fe(2+) and manganese, not Fe(3+) or copper. Metal ion transport is electrogenic and proton dependent. By contrast, Nramp2 transports only Fe(2+) in a non-electrogenic and proton-independent way. These differences reflect evolutionary divergence of the prototypical Nramp2 protein sequence compared to the archetypical Nramp1 and DMT1 proteins.

Amino acid transporter B(0)AT1 (slc6a19) and ancillary protein: impact on function.

Amino acids play an important role in the metabolism of all organisms. Their epithelial re-absorption is due to specific transport proteins, such as B(0)AT1, a Na(+)-coupled neutral amino acid symporter belonging to the solute carrier 6 family. Here, a recently cloned fish orthologue, from the intestine of Salmo salar, was electrophysiologically characterized with the two-electrode voltage clamp technique, in Xenopus laevis oocytes heterologously expressing the transporter. Substrate specificity, apparent affinities and the ionic dependence of the transport mechanism were determined in the presence of specific collectrin. Results demonstrated that like the human, but differently from sea bass (Dicentrarchus labrax) orthologue, salmon B(0)AT1 needs to be associated with partner proteins to be correctly expressed at the oocyte plasma membrane. Cloning of sea bass collectrin and comparison of membrane expression and functionality of the B(0)AT1 orthologue transporters allowed a deeper investigation on the role of their interactions. The parameters acquired by electrophysiological and immunolocalization experiments in the mammalian and fish transporters contributed to highlight the dynamic of relations and impacts on transport function of the ancillary proteins. The comparative characterization of the physiological parameters of amino acid transporters with auxiliary proteins can help the comprehension of the regulatory mechanism of essential nutrient absorption.

Hyperpolarization-activated cyclic nucleotide-gated channels in peripheral diaphragmatic lymphatics.

Diaphragmatic lymphatic function is mainly sustained by pressure changes in the tissue and serosal cavities during cardiorespiratory cycles. The most peripheral diaphragmatic lymphatics are equipped with muscle cells (LMCs), which exhibit spontaneous contraction, whose molecular machinery is still undetermined. Hypothesizing that spontaneous contraction might involve hyperpolarization-activated cyclic nucleotide-gated (HCN) channels in lymphatic LMCs, diaphragmatic specimens, including spontaneously contracting lymphatics, were excised from 33 anesthetized rats, moved to a perfusion chamber containing HEPES-Tyrode's solution, and treated with HCN channels inhibitors cesium chloride (CsCl), ivabradine, and ZD-7288. Compared with control, exposure to 10 mM CsCl reduced (-65%, n = 13, P < 0.01) the contraction frequency (FL) and increased end-diastolic diameter (DL-d, +7.3%, P < 0.01) without changes in end-systolic diameter (DL-s). Ivabradine (300 µM) abolished contraction and increased DL-d (-14%, n = 10, P < 0.01) or caused an incomplete inhibition of FL (n = 3, P < 0.01), leaving DL-d and DL-s unaltered. ZD-7288 (200 µM) completely (n = 12, P < 0.01) abolished FL, while DL-d decreased to 90.9 ± 2.7% of control. HCN gene expression and immunostaining confirmed the presence of HCN1-4 channel isoforms, likely arranged in different configurations, in LMCs. Hence, all together, data suggest that HCN channels might play an important role in affecting contraction frequency of LMCs.

TAS2R38 taste receptor gene and chronic rhinosinusitis: new data from an Italian population.

BACKGROUND: Chronic rhinosinusitis (CRS) is a frequent disease with high social impact and multifactorial pathogenesis. Recently, single nucleotide polymorphisms within the TAS2R38 gene have been implicated as possible contributors to the complex gene-environment interactions in CRS. The purpose of this study was to confirm the proposed correlation between TAS2R38 genotype, CRS and related comorbidities. METHODS: Fifty-three CRS patients and 39 healthy individuals were genotyped at the TAS2R38 locus. CRS patients were treated by endoscopic sinus surgery and medical therapies and subdivided in CRS with nasal polyps (CRSwNPs) and CRS without nasal polyps (CRSsNPs). The effect of genotype on CRS and CRS-related comorbidities was assessed. RESULTS: The distribution of the different genotypes at the TAS2R38 locus was not significantly different between CRS patients, either with or without nasal polyps, and controls. Besides, no association was found between the different genotypes at the TAS2R38 locus and CRS-related comorbidities. CONCLUSIONS: No association was found between TAS2R38 alleles or genotypes and CRS, thus questioning its role in the pathogenesis of CRS.

Natural antisense transcript for hyaluronan synthase 2 (HAS2-AS1) induces transcription of HAS2 via protein O-GlcNAcylation.

Changes in the microenvironment organization within vascular walls are critical events in the pathogenesis of vascular pathologies, including atherosclerosis and restenosis. Hyaluronan (HA) accumulation into artery walls supports vessel thickening and is involved in many cardiocirculatory diseases. Excessive cytosolic glucose can enter the hexosamine biosynthetic pathway, increase UDP-N-acetylglucosamine (UDP-GlcNAc) availability, and lead to modification of cytosolic proteins via O-linked attachment of the monosaccharide ß-N-GlcNAc (O-GlcNAcylation) from UDP-GlcNAc by the enzyme O-GlcNAc transferase. As many cytoplasmic and nuclear proteins can be glycosylated by O-GlcNAc, we studied whether the expression of the HA synthases that synthesize HA could be controlled by O-GlcNAcylation in human aortic smooth muscle cells. Among the three HAS isoenzymes, only HAS2 mRNA increased after O-GlcNAcylation induced by glucosamine treatments or by inhibiting O-GlcNAc transferase with PUGNAC (O-(2-acetamido-2-deoxy-d-glucopyranosylidene)amino-N-phenylcarbamate). We found that the natural antisense transcript of HAS2 (HAS2-AS1) was absolutely necessary to induce the transcription of the HAS2 gene. Moreover, we found that O-GlcNAcylation modulated HAS2-AS1 promoter activation by recruiting the NF-κB subunit p65, but not the HAS2 promoter, whereas HAS2-AS1 natural antisense transcript, working in cis, regulated HAS2 transcription by altering the chromatin structure around the HAS2 proximal promoter via O-GlcNAcylation and acetylation. These results indicate that HAS2 transcription can be finely regulated not only by recruiting transcription factors to the promoter as previously described but also by modulating chromatin accessibility by epigenetic modifications.

Microenvironmental control of malignancy exerted by RNASET2, a widely conserved extracellular RNase.

A recent body of evidence indicates an active role for stromal (mis)-regulation in the progression of neoplasias. Within this conceptual framework, genes belonging to the growing but still poorly characterized class of tumor antagonizing/malignancy suppressor genes (TAG/MSG) seem to play a crucial role in the regulation of the cross-talk between stromal and epithelial cells by controlling malignant growth in vivo without affecting any cancer-related phenotype in vitro. Here, we have functionally characterized the human RNASET2 gene, which encodes the first human member of the widespread Rh/T2/S family of extracellular RNases and was recently found to be down-regulated at the transcript level in several primary ovarian tumors or cell lines and in melanoma cell lines. Although we could not detect any activity for RNASET2 in several functional in vitro assays, a remarkable control of ovarian tumorigenesis could be detected in vivo. Moreover, the control of ovarian tumorigenesis mediated by this unique tumor suppressor gene occurs through modification of the cellular microenvironment and the induction of immunocompetent cells of the monocyte/macrophage lineage. Taken together, the data presented in this work strongly indicate RNASET2 as a previously unexplored member of the growing family of tumor-antagonizing genes.

Functional properties of a newly cloned fish ortholog of the neutral amino acid transporter B0AT1 (SLC6A19).

The functional properties of an ortholog of the B(0)AT1 (SLC6A19) amino acid transporter, cloned from the intestine of the sea bass Dicentrachus labrax, were investigated. The two-electrode voltage-clamp technique was applied to Xenopus laevis oocytes heterologously expressing the transporter in order to measure the currents associated with the transport process in different conditions. In particular the substrate specificity, the ionic requirements, and possible effects of pH were examined. Among the organic substrates, leucine, glycine, serine and valine generated the largest transport currents with apparent affinities in the lower millimolar range. The importance of Na(+) as the driver ion in the transport process is confirmed, although Li(+) is also capable to sustain transport, while K(+) is not. No evidence of a relevant role of Cl(-) in the transport activity was found. Concerning the other two kinds of currents commonly found in electrogenic transporters, very fast pre-steady-state currents were detected in the absence of organic substrate, while lithium-specific leak currents were not observed. The comparison of these properties with those of the mammalian and insect orthologs may give interesting indication for future structure-function studies in this transporter subfamily.

Characterization of the transport of lysine-containing dipeptides by PepT1 orthologs expressed in Xenopus laevis oocytes.

During digestion, dietary proteins cleaved in di and tri-peptides are translocated from the intestinal lumen into the enterocytes via PepT1 (SLC15A1) using an inwardly directed proton electrochemical gradient. The kinetic properties in various PepT1 orthologs (Dicentrarchus labrax, Oryctolagus cuniculus, Danio rerio) have been explored to determine the transport efficiency of different combinations of lysine, methionine, and glycine. Species-specific differences were observed. Lys-Met resulted the best substrate at all tested potentials in sea bass and rabbit PepT1, whereas in the zebrafish transporter all tested dipeptides (except Gly-Lys) elicited similar currents independently on the charge position or amino acid composition. For the sea bass and rabbit PepT1, kinetic parameters, K(0.5) and I(max) and their ratio, show the importance of the position of the charged lysine in the peptide. The PepT1 transporter of these species has very low affinity for Lys-Lys and Gly-Lys; this reduces the transport efficiency which is instead higher for Lys-Met and Lys-Gly. PepT1 from zebrafish showed relatively high affinity and excellent transport efficiency for Met-Lys and Lys-Met. These data led us to speculate about the structural determinants involved in substrate interaction according to the model proposed for this transporter.

The "www" of Xenopus laevis Oocytes: The Why, When, What of Xenopus laevis Oocytes in Membrane Transporters Research.

After 50 years, the heterologous expression of proteins in Xenopus laevis oocytes is still essential in many research fields. New approaches and revised protocols, but also classical methods, such as the two-electrode voltage clamp, are applied in studying membrane transporters. New and old methods for investigating the activity and the expression of Solute Carriers (SLC) are reviewed, and the kinds of experiment that are still useful to perform with this kind of cell are reported. Xenopus laevis oocytes at the full-grown stage have a highly efficient biosynthetic apparatus that correctly targets functional proteins at the defined compartment. This small protein factory can produce, fold, and localize almost any kind of wild-type or recombinant protein; some tricks are required to obtain high expression and to verify the functionality. The methodologies examined here are mainly related to research in the field of membrane transporters. This work is certainly not exhaustive; it has been carried out to be helpful to researchers who want to quickly find suggestions and detailed indications when investigating the functionality and expression of the different members of the solute carrier families.

Comparison of the baculovirus-insect cell and Pichia pastoris heterologous systems for the expression of the human tumor suppressor protein RNASET2.

We report the expression of recombinant RNASET2, the only human member of the Rh/T2/S family of acid ribonucleases, in the yeast Pichia pastoris and the baculovirus-insect cell heterologous systems. In both models, the yield of recombinant protein was comparable and ranged between 5 mg/L (for a catalytically impaired mutant version of RNASET2) and 30 mg/L for the wild-type protein. Thus, the produced protein version rather than the expression system used appears to influence protein yield after optimization of culture conditions. The recombinant protein was found to undergo heterogeneous glycosylation in both systems, particularly in P. pastoris. Most importantly, the wild-type protein purified from both systems was found to be catalytically competent. The expression of recombinant RNASET2 in both systems will allow the implementation of functional assays in vivo and in vitro to better define the antioncogenic properties of this member of the Rh/T2/S ribonuclease family.

Characterization of Transport Activity of SLC11 Transporters in Xenopus laevis Oocytes by Fluorophore Quenching.

Membrane proteins are involved in different physiological functions and are the target of pharmaceutical and abuse drugs. Xenopus laevis oocytes provide a powerful heterologous expression system for functional studies of these proteins. Typical experiments investigate transport using electrophysiology and radiolabeled uptake. A two-electrode voltage clamp is suitable only for electrogenic proteins, and uptake measurements require the existence of radiolabeled substrates and adequate laboratory facilities.Recently, Dictyostelium discoideum Nramp1 and NrampB were characterized using multidisciplinary approaches. NrampB showed no measurable electrogenic activity, and it was investigated in Xenopus oocytes by acquiring confocal images of the quenching of injected fluorophore calcein.This method is adequate to measure the variation in emitted fluorescence, and thus transporter activity indirectly, but requires long experimental procedures to collect statistically consistent data. Considering that optimal expression of heterologous proteins lasts for 48-72 h, a slow acquiring process requires the use of more than one batch of oocytes to complete the experiments. Here, a novel approach to measure substrate uptake is reported. Upon injection of a fluorophore, oocytes were incubated with the substrate and the transport activity measured, evaluating fluorescence quenching in a microplate reader. The technique permits the testing of tens of oocytes in different experimental conditions simultaneously, and thus the collection of significant statistical data for each batch, saving time and animals.The method was tested with different metal transporters (SLC11), DMT1, DdNramp1, and DdNrampB, and verified with the peptide transporter PepT1 (SLC15). Comparison with traditional methods (uptake, two-electrode voltage clamp) and with quenching images acquired by fluorescence microscopy confirmed its efficacy.

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

[This corrects the article DOI: 10.1186/s12263-019-0657-3.].

Myocardial overexpression of ANKRD1 causes sinus venosus defects and progressive diastolic dysfunction.

AIMS: Increased Ankyrin Repeat Domain 1 (ANKRD1) levels linked to gain of function mutations have been associated to total anomalous pulmonary venous return and adult cardiomyopathy occurrence in humans. The link between increased ANKRD1 level and cardiac structural and functional disease is not understood. To get insight into this problem, we have generated a gain of function ANKRD1 mouse model by overexpressing ANKRD1 in the myocardium. METHODS AND RESULTS: Ankrd1 is expressed non-homogeneously in the embryonic myocardium, with a dynamic nucleo-sarcomeric localization in developing cardiomyocytes. ANKRD1 transgenic mice present sinus venosus defect, which originates during development by impaired remodelling of early embryonic heart. Adult transgenic hearts develop diastolic dysfunction with preserved ejection fraction, which progressively evolves into heart failure, as shown histologically and haemodynamically. Transgenic cardiomyocyte structure, sarcomeric assembly, and stability are progressively impaired from embryonic to adult life. Postnatal transgenic myofibrils also present characteristic functional alterations: impaired compliance at neonatal stage and impaired lusitropism in adult hearts. Altogether, our combined analyses suggest that impaired embryonic remodelling and adult heart dysfunction in ANKRD1 transgenic mice present a common ground of initial cardiomyocyte defects, which are exacerbated postnatally. Molecular analysis showed transient activation of GATA4-Nkx2.5 transcription in early transgenic embryos and subsequent dynamic transcriptional modulation within titin gene. CONCLUSIONS: ANKRD1 is a fine mediator of cardiomyocyte response to haemodynamic load in the developing and adult heart. Increased ANKRD1 levels are sufficient to initiate an altered cellular phenotype, which is progressively exacerbated into a pathological organ response by the high ventricular workload during postnatal life. Our study defines for the first time a unifying picture for ANKRD1 role in heart development and disease and provides the first mechanistic link between ANKRD1 overexpression and cardiac disease onset.

In silico prediction and experimental validation of natural antisense transcripts in two cancer-associated regions of human chromosome 6.

Antisense transcription has long been recognized as a mechanism involved in the regulation of gene expression. Therefore, several human diseases associated with abnormal patterns of gene expression might display antisense RNA-mediated pathogenetic mechanisms. Such issue could be particularly relevant for cancer pathogenesis, since deregulated gene expression has long been established as a hallmark of cancer cells. Herein, we report on a bioinformatic search for antisense transcription in two cancer-associated regions of human chromosome 6 (6q21 and 6q27). Natural antisense transcripts (NATs) for several genes in both genomic regions were predicted in silico and subsequently validated by strand-specific RT-PCR. Detailed experimental validation by quantitative real-time RT-PCR of five putative cancer related sense-antisense transcript pairs revealed a single candidate tumor suppressor gene (RPS6KA2) whose expression levels display marked cancer-related changes that are likely mediated by its antisense RNA in a breast cancer cell line model.

Serum miR-223: A Validated Biomarker for Detection of Early-Stage Non-Small Cell Lung Cancer.

BACKGROUND: The published circulating miRNA signatures proposed for early-stage non-small cell lung cancer (NSCLC) detection are inconsistent and difficult to replicate. Reproducibility and validation of an miRNA simple signature of NSCLC are prerequisites for translation to clinical application. METHODS: The serum level of miR-223 and miR-29c, emerging from published studies, respectively, as a highly sensitive and a highly specific biomarker of early-stage NSCLC, was measured with droplet digital PCR (ddPCR) technique in an Italian cohort of 75 patients with stage I-II NSCLC and 111 tumor-free controls. By ROC curve analysis we evaluated the miR-223 and miR-29c performance in discerning NSCLC cases from healthy controls. RESULTS: Reproducibility and robust measurability of the two miRNAs using ddPCR were documented. In a training set (40 stage I-II NSCLCs and 56 controls), miR-223 and miR-29c, respectively, showed an AUC of 0.753 [95% confidence interval (CI), 0.655-0.836] and 0.632 (95% CI, 0.527-0.729) in identifying NSCLC. Combination of miR-223 with miR-29c yielded an AUC of 0.750, not improved over that of miR-223 alone. Furthermore, in an independent blind set (35 stage I-II NSCLCs and 55 controls), we validated serum miR-223 as an effective biomarker of stage I-II NSCLC (AUC = 0.808; 95% CI, 0.712-0.884), confirming the miR-223 diagnostic performance reported by others in Chinese cohorts. CONCLUSIONS: Using ddPCR technology, miR-223 was externally validated as a reproducible, effective serum biomarker of early-stage NSCLC in ethnically different subjects. Combination with miR-29c did not improve the miR-223 diagnostic performance. IMPACT: Serum miR-223 determination may be proposed as a tool for refining NSCLC risk stratification, independent of smoking habit and age.

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

BACKGROUND: Peptide 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). RESULTS: Here, 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 K 0.5 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. CONCLUSIONS: We 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.