Genetic and Mechanical Regulation of Intestinal Smooth Muscle Development.

The gastrointestinal tract is enveloped by concentric and orthogonally aligned layers of smooth muscle; however, an understanding of the mechanisms by which these muscles become patterned and aligned in the embryo has been lacking. We find that Hedgehog acts through Bmp to delineate the position of the circumferentially oriented inner muscle layer, whereas localized Bmp inhibition is critical for allowing formation of the later-forming, longitudinally oriented outer layer. Because the layers form at different developmental stages, the muscle cells are exposed to unique mechanical stimuli that direct their alignments. Differential growth within the early gut tube generates residual strains that orient the first layer circumferentially, and when formed, the spontaneous contractions of this layer align the second layer longitudinally. Our data link morphogen-based patterning to mechanically controlled smooth muscle cell alignment and provide a mechanistic context for potentially understanding smooth muscle organization in a wide variety of tubular organs.

Deep into the niche: Deciphering local endoderm-microenvironment interactions in development, homeostasis, and disease of pancreas and intestine.

Unraveling molecular and functional heterogeneity of niche cells within the developing endoderm could resolve mechanisms of tissue formation and maturation. Here, we discuss current unknowns in molecular mechanisms underlying key developmental events in pancreatic islet and intestinal epithelial formation. Recent breakthroughs in single-cell and spatial transcriptomics, paralleled with functional studies in vitro, reveal that specialized mesenchymal subtypes drive the formation and maturation of pancreatic endocrine cells and islets via local interactions with epithelium, neurons, and microvessels. Analogous to this, distinct intestinal niche cells regulate both epithelial development and homeostasis throughout life. We propose how this knowledge can be used to progress research in the human context using pluripotent stem cell-derived multilineage organoids. Overall, understanding the interactions between the multitude of microenvironmental cells and how they drive tissue development and function could help us make more therapeutically relevant in vitro models.

Identification of Key Genes in Fetal Gut Development at Single-Cell Level by Exploiting Machine Learning Techniques.

The study of fetal gut development is critical due to its substantial influence on immediate neonatal and long-term adult health. Current research largely focuses on microbiome colonization, gut immunity, and barrier function, alongside the impact of external factors on these phenomena. Limited research has been dedicated to the categorization of developing fetal gut cells. Our study aimed to enhance our understanding of fetal gut development by employing advanced machine-learning techniques on single-cell sequencing data. This dataset consisted of 62,849 samples, each characterized by 33,694 distinct gene features. Four feature ranking algorithms were utilized to sort features according to their significance, resulting in four feature lists. Then, these lists were fed into an incremental feature selection method to extract essential genes, classification rules, and build efficient classifiers. Several important genes were recognized by multiple feature ranking algorithms, such as FGG, MDK, RBP1, RBP2, IGFBP7, and SPON2. These features were key in differentiating specific developing intestinal cells, including epithelial, immune, mesenchymal, and vasculature cells of the colon, duo jejunum, and ileum cells. The classification rules showed special gene expression patterns on some intestinal cell types and the efficient classifiers can be useful tools for identifying intestinal cells.

Syntaxin5 is essential for survival by ensuring midgut epithelial homeostsis and regulating feeding in Locusta migratoria.

Syntaxin5 (Syx5) belongs to SNAREs family, which play important roles in fusion of vesicles to target membranes. Most of what we know about functions of Syx5 originates from studies in fungal or vertebrate cells, how Syx5 operates during the development of insects is poorly understood. In this study, we investigated the role of LmSyx5 in the gut development of the hemimetabolous insect Locusta migratoria. LmSyx5 was expressed in many tissues, with higher levels in the gut. Knockdown of LmSyx5 by RNA interference (RNAi) considerably suppressed feeding in both nymphs and adults. The dsLmSyx5-injected locusts lost body weight and finally died at a mortality of 100%. Furthermore, hematoxylin-eosin staining indicated that the midgut is deformed in dsLmSyx5-treated nymphs and the brush border in midgut epithelial cells is severely damaged, suggesting that LmSyx5 is involved in morphogenesis of the midgut. TEM further showed that the endoplasmic reticulum of midgut cells have a bloated appearance. Taken together, these results suggest that LmSyx5 is essential for midgut epithelial homeostsis that affects growth and development of L. migratoria. Thus, Syx5 is a promising RNAi target for controlling L. migratoria, and even other pests.

Benzodiazepine Interference with Fertility and Embryo Development: A Preliminary Survey in the Sea Urchin Paracentrotus lividus.

Psychotropic drugs and benzodiazepines are nowadays among the primary substances of abuse. This results in a large and constant release into aquatic environments where they have potentially harmful effects on non-target organisms and, eventually, human health. In the last decades, evidence has been collected on the possible interference of benzodiazepines with reproductive processes, but data are few and incomplete. In this study, the possible negative influence of delorazepam on fertilization and embryo development has been tested in Paracentrotus lividus, a key model organism in studies of reproduction and embryonic development. Sperm, eggs, or fertilized eggs have been exposed to delorazepam at three concentrations: 1 µg/L (environmentally realistic), 5 µg/L, and 10 µg/L. Results indicate that delorazepam reduces the fertilizing capacity of male and female gametes and interferes with fertilization and embryo development. Exposure causes anatomical anomalies in plutei, accelerates/delays development, and alters the presence and distribution of glycoconjugates such as N-Acetyl-glucosamine, α-linked fucose, and α-linked mannose in both morulae and plutei. These results should attract attention to the reproductive fitness of aquatic species exposed to benzodiazepines and pave the way for further investigation of the effects they may exert on human fertility. The presence of benzodiazepines in the aquatic environment raises concerns about the reproductive well-being of aquatic species. Additionally, it prompts worries regarding potential impacts on human fertility due to the excessive use of anxiolytics.

Characterization of a novel Hoxa5eGFP mouse line.

BACKGROUND: Hox genes encode transcription factors that are important for establishing the body plan. Hoxa5 is a member of the mammalian Hox5 paralogous group that regulates the patterning and morphology of the cervical-thoracic region of the axial skeleton. Hoxa5 also plays crucial functions in lung morphogenesis. RESULTS: We generated a Hoxa5eGFP reporter mouse line using CRISPR technology, allowing real-time visualization of Hoxa5 expression. Hoxa5eGFP recapitulates reported embryonic Hoxa5 mRNA expression patterns. Specifically, Hoxa5eGFP can be visualized in the developing mouse neural tube, somites, lung, diaphragm, foregut, and midgut, among other organs. In the stomach, posteriorly biased Hoxa5eGFP expression correlates with a drastic morphological reduction of the corpus in Hox5 paralogous mutants. Expression of Hoxa5eGFP in the lung continues in all lung fibroblast populations through postnatal and adult stages. CONCLUSIONS: We identified cell types that express Hoxa5 in postnatal and adult mouse lungs, including various fibroblasts and vascular endothelial cells. This reporter line will be a powerful tool for studies of the function of Hoxa5 during mouse development, homeostasis, and disease processes.

The role of the 5' HoxA genes in the development of the hindgut, vent, and a novel sphincter in a derived teleost (bluebanded goby, Lythrypnus dalli).

Unique expression patterns of the 5' HoxA genes are associated with the evolution and development of novel features including claspers in cartilaginous fishes, modified pectoral fins in batoids, and the yolk sac extension in Cypriniformes. Here, we demonstrate a role for HoxA11a and HoxA13a in demarcating the hindgut in fishes of the family Gobiidae, including a novel sphincter called the intestinal rectal sphincter (IRS). Disruption of 5' HoxA expression, via manipulation of retinoic acid signaling, results in failure of the IRS and/or vent to develop. Furthermore, exposure to HoxA disruptors alters 5' HoxA expression, in association with developmental phenotypes, demonstrating a functional link between 5' HoxA expression and development of a novel feature in the bluebanded goby, Lythrypnus dalli.

Early patterning of ABCB, ABCC, and ABCG transporters establishes unique territories of small molecule transport in embryonic mesoderm and endoderm.

Directed intercellular movement of diverse small molecules, including metabolites, signal molecules and xenobiotics, is a key feature of multicellularity. Networks of small molecule transporters (SMTs), including several ATP Binding Cassette (ABC) transporters, are central to this process. While small molecule transporters are well described in differentiated organs, little is known about their patterns of expression in early embryogenesis. Here we report the pattern of ABC-type SMT expression and activity during the early development of sea urchins. Of the six major ABCs in this embryo (ABCB1, -B4, -C1, -C4, -C5 and -G2), three expression patterns were observed: 1) ABCB1 and ABCC1 are first expressed ubiquitously, and then become enriched in endoderm and ectoderm-derived structures. 2) ABCC4 and ABCC5 are restricted to a ring of mesoderm in the blastula and ABCC4 is later expressed in the coelomic pouches, the embryonic niche of the primordial germ cells. 3) ABCB4 and ABCG2 are expressed exclusively in endoderm-fated cells. Assays with fluorescent substrates and inhibitors of transporters revealed a ring of ABCC4 efflux activity emanating from ABCC4+ mesodermal cells. Similarly, ABCB1 and ABCB4 efflux activity was observed in the developing gut, prior to the onset of feeding. This study reveals the early establishment of unique territories of small molecule transport during embryogenesis. A pattern of ABCC4/C5 expression is consistent with signaling functions during gut invagination and germ line development, while a later pattern of ABCB1/B4 and ABCG2 is consistent with roles in the embryonic gut. This work provides a conceptual framework with which to examine the function and evolution of SMT networks and to define the specific developmental pathways that drive the expression of these genes.

Effects of dietary protein on gut development, microbial compositions and mucin expressions in mice.

AIMS: Dietary protein, as an important macronutrient, widely participates in host growth and metabolism. In this study, effects of different protein levels (14, 20 and 26%) on the gut development, microbial compositions and mucin expressions were studied in C57BL/6 mice. METHODS AND RESULTS: The results showed that body weight and the relative weight of stomach and gut were decreased in low-protein diet-fed mice, whereas high-protein diet significantly reduced the villus length and area of jejunum. Goblet cells number in the jejunum was reduced in the low-protein group, which was reversed by dietary a high-protein diet. In addition, high-protein diet notably reduced microbial diversity and changed the microbial compositions at the phylum level, such as Bacteroides, Proteobacteria, Actinomycetes and Deferribacteres. Furthermore, high-protein diet significantly increased mucin2, mucin3 and mucin4 expressions in the jejunum, but downregulated mucin1, mucin2, mucin4 and TFF3 in the ileum, indicating a tissue-dependent manner. CONCLUSIONS: Together, high-protein diet may impair gut development, microbial balance and mucin system, and a low-protein diet is suggested to promote a healthy lifestyle. SIGNIFICANCE AND IMPACT OF STUDY: Mucin influenced gut development (villus index and goblet cell number) through remodelling gut microbes, as low and high protein levels resulted in contrary expression levels of mucin in jejunum and ileum.

Gene- and tissue-level interactions in normal gastrointestinal development and Hirschsprung disease.

The development of the gut from endodermal tissue to an organ with multiple distinct structures and functions occurs over a prolonged time during embryonic days E10.5-E14.5 in the mouse. During this process, one major event is innervation of the gut by enteric neural crest cells (ENCCs) to establish the enteric nervous system (ENS). To understand the molecular processes underpinning gut and ENS development, we generated RNA-sequencing profiles from wild-type mouse guts at E10.5, E12.5, and E14.5 from both sexes. We also generated these profiles from homozygous Ret null embryos, a model for Hirschsprung disease (HSCR), in which the ENS is absent. These data reveal 4 major features: 1) between E10.5 and E14.5 the developmental genetic programs change from expression of major transcription factors and its modifiers to genes controlling tissue (epithelium, muscle, endothelium) specialization; 2) the major effect of Ret is not only on ENCC differentiation to enteric neurons but also on the enteric mesenchyme and epithelium; 3) a muscle genetic program exerts significant effects on ENS development; and 4) sex differences in gut development profiles are minor. The genetic programs identified, and their changes across development, suggest that both cell autonomous and nonautonomous factors, and interactions between the different developing gut tissues, are important for normal ENS development and its disorders.

Performance and visceral tissue growth and development of Holstein calves fed differing milk replacer allowances and starch concentrations in pelleted starter.

The objectives of this study were to investigate how milk replacer (MR) allowance and differing concentrations of starch and neutral detergent fiber in starter alters visceral tissue and overall growth of the calf. Calves were randomly assigned to 1 of 4 dietary treatments (n = 12 per treatment) arranged in a 2 × 2 factorial based on daily MR allowance (MRA) and amount of starch in pelleted starter (SPS) as follows: 0.691 kg of MR/d [dry matter (DM) basis] with starter containing low or high starch (12.0% and 35.6% starch, respectively) and 1.382 kg of MR/day (DM) with starter containing low or high starch. All calves were housed in individual pens with straw bedding until wk 5 when bedding was covered to minimize intake. Calves were fed MR twice daily (0700 and 1700 h) containing 24.5% crude protein (DM) and 19.8% fat (DM), and had access to pelleted starter (increased by 50 g/d if there were no refusals before weaning, and then 200 g/d during and after weaning) and water starting on d 1. Calves arrived between 1 and 3 d of age and were enrolled into an 8-wk study, with calves undergoing step-down weaning during wk 7. Intakes were measured daily, and body weight (BW) and blood samples were recorded and collected weekly. Calves were dissected in wk 8 for visceral tissue measurements. Overall, there was increased MR DM intake for the high- (0.90 ± 0.01 kg/d; ± SE) compared with the low-MRA (0.54 ± 0.01 kg/d) calves, whereas starter DM intake increased in low- (0.47 ± 0.05 kg/d) compared with high-MRA (0.20 ± 0.05 kg/d) calves, which was driven by increases in wk 6, 7, and 8. High-MRA calves had increased BW during wk 2, 3, 4, 5, 6, and 7. The difference in BW disappeared by wk 8, with overall average daily gain having a tendency to be increased in high (0.57 ± 0.04 kg/d) compared with low-MRA (0.50 ± 0.04 kg/d) calves, whereas average daily gain was increased in high-MRA calves during wk 2 and 3 and increased in low-MRA calves during wk 7 and 8. There were several differences throughout visceral tissue measurements, but most notably, an increase in rumen mass (i.e., full, empty, and digesta weights) in low- compared with high-MRA calves, as well as in low- compared with high-SPS calves was observed. The length, width, and 2-dimensional area of rumen papillae were also increased in low- (area: 0.88 ± 0.03 mm2) compared with high-MRA (0.46 ± 0.03 mm2) calves. The majority of differences were attributed to increased MR allowance, which contributed to reduced pelleted starter intake by more than 50% and reduced rumen development, whereas differences in starch intake from the completely pelleted starter had minimal effects on overall growth and tissue measurements.

A Mixture of Valine and Isoleucine Restores the Growth of Protein-Restricted Pigs Likely through Improved Gut Development, Hepatic IGF-1 Pathway, and Plasma Metabolomic Profile.

Valine (Val) alone or in combination with isoleucine (Ile) improves the growth under severe protein restriction; however, the underlying mechanisms remain unknown. In this study, we assessed whether Val/Ile-induced growth in protein-restricted pigs is associated with changes in gut development, hepatic insulin-like growth factor 1 (IGF-1) production, and blood metabolomics. Forty piglets were assigned to five dietary groups: positive control (PC) with standard protein content; low protein (LP) with very low protein content; and LP supplemented with Val (LPV), Ile (LPI), and Val and Ile (LPVI). LPVI reversed the negative effects of VLP diets on growth and gut morphology. Both LPV and LPVI restored the reduced transcript of IGF-1 while decreasing the transcript of insulin-like growth factor binding protein 1 (IGFBP1) in the liver. LPV and LPVI recovered the reduced plasma Val, glycine, and leucine concentrations, which were positively correlated with improved gut morphology and the hepatic IGF-1 gene expression and negatively correlated with hepatic IGFBP1 mRNA abundance. In conclusion, supplementation with a combination of Val and Ile into the VLP diets restored the decreased growth performance of pigs fed with these diets likely through improved gut development, hepatic IGF-1 expression and bioavailability, and plasma metabolomics profile.

Effects of oral sialic acid on gut development, liver function and gut microbiota in mice.

Sialic acid (N-acetylneuraminic acid), a 9-carbon monosaccharide, has been widely studied in immunology, oncology and neurology. However, the effects of sialic acid on organ and intestinal development, liver function and gut microbiota were rarely studied. In this study, we found that oral sialic acid tended to increase the relative weight of liver and decreased the serum aspartate aminotransferase (GPT) activity. In addition, sialic acid treatment markedly reduced gut villus length, depth, the ratio of villus length/depth (L/D), areas, width and the number of goblet cells. Furthermore, gut microbes were changed in response to oral sialic acid, such as Staphylococcus lentus, Corynebacterium stationis, Corynebacterium urealyticum, Jeotgalibaca sp_PTS2502, Ignatzschineria indica, Sporosarcina pasteurii, Sporosarcina sp_HW10C2, Facklamia tabacinasalis, Oblitimonas alkaliphila, Erysipelatoclostridium ramosum, Blautia sp_YL58, Bacteroids thetaiotaomicron, Morganella morganii, Clostridioides difficile, Helicobacter tryphlonius, Clostridium sp_Clone47, Alistipes finegoldii, [pseudomonas]_geniculata and Pseudomonas parafulva at the species level. In conclusion, oral sialic acid altered the intestinal pathological state and microbial compositions, and the effect of sialic acid on host health should be further studied.

A ras-related nuclear protein Ran participates in the 20E signaling pathway and is essential for the growth and development of Locusta migratoria.

The small GTPase Ran is a member of the Ras superfamily of small GTP-binding proteins, which plays a key role in the translocation of RNA and proteins through the nuclear pore complex. In this study, the full-length cDNA sequence of LmRan gene was obtained, which consists of 648-nucleotides open reading frame (ORF) and encodes 215 amino acids. RT-qPCR results revealed that LmRan was expressed in all developmental days and tissues investigated. Injection of dsLmRan into 4th and 5th instar nymphs, resulted in a significant down-regulation of LmRan transcripts, respectively. All dsLmRan-injected nymphs died before molting. Further hematoxylin and eosin staining of the integument showed that there was no apolysis occurred after silencing LmRan. In addition, the weight of dsLmRan-injected nymphs was significantly lower than that of the control group, and the gastric caecum and midgut was severely smaller. Especiallly, the mRNA level of LmCYP302a1, LmCYP315a1 and LmCYP314a1 responsible for 20E synthesis, LmE75 and LmE74 genes involved in the 20E signaling pathway, LmGfat, LmUAP1 and LmCHT10 genes involved in chitin metabolism pathway were dramatically decreased in the dsLmRan-injected nymphs. Together, the results indicated that LmRan participate in the 20E signaling pathway, which is essential for the growth and development of locusts.

Probiotic and nutritional effects of Debaryomyces hansenii on animals.

Debaryomyces hansenii comes of age as a new potential probiotic for terrestrial and aquatic animals. Probiotic properties, including inmunostimulatory effects, gut microbiota modulation, enhanced cell proliferation and differentiation, and digestive function improvements have been related to the oral delivery of D. hansenii. Its functional compounds, such as cell wall components and polyamines, have been identified and implicated in its immunomodulatory activity. In addition, in vitro studies using immune cells have shown standpoints on the possible recognition, regulation, and effector immune mechanisms stimulated by this yeast. This review describes historic, cutting-edge research findings, implications, and perspectives on the use of D. hansenii as a promising probiotic for animals. KEY POINTS: • Debaryomyces hansenii has probiotic effects in terrestrial and aquatic animals. • Nutritional effects could be associated to probiotic D. hansenii strains. • ß-D-Glucan and polyamines from D. hansenii are associated to probiotic properties. • Adoption by the industry is expected in the next years.

Enteric nervous system development: A crest cell's journey from neural tube to colon.

The enteric nervous system (ENS) is comprised of a network of neurons and glial cells that are responsible for coordinating many aspects of gastrointestinal (GI) function. These cells arise from the neural crest, migrate to the gut, and then continue their journey to colonize the entire length of the GI tract. Our understanding of the molecular and cellular events that regulate these processes has advanced significantly over the past several decades, in large part facilitated by the use of rodents, avians, and zebrafish as model systems to dissect the signals and pathways involved. These studies have highlighted the highly dynamic nature of ENS development and the importance of carefully balancing migration, proliferation, and differentiation of enteric neural crest-derived cells (ENCCs). Proliferation, in particular, is critically important as it drives cell density and speed of migration, both of which are important for ensuring complete colonization of the gut. However, proliferation must be tempered by differentiation among cells that have reached their final destination and are ready to send axonal extensions, connect to effector cells, and begin to produce neurotransmitters or other signals. Abnormalities in the normal processes guiding ENCC development can lead to failure of ENS formation, as occurs in Hirschsprung disease, in which the distal intestine remains aganglionic. This review summarizes our current understanding of the factors involved in early development of the ENS and discusses areas in need of further investigation.

Duplicated FoxA genes in the leech Helobdella: Insights into the evolution of direct development in clitellate annelids.

BACKGROUND: As an adaptation to the land, the clitellate annelid had reorganized its embryogenesis to develop "directly" without the ancestral planktonic larval stage. To study the evolution of gut development in the directly developing clitellates, we characterized the expression pattern of the conserved gut gene, FoxA, in the embryonic development of the leech. RESULTS: The leech has three FoxA paralogs. Hau-FoxA1 is first expressed in a subset of endoderm cells and then in the foregut and the midgut. Hau-FoxA2 is expressed in the stomodeum, which is secondarily derived from the anterior ectoderm in the clitellates rather than the tissue around the blastopore, the ancestral site of mouth formation in Phylum Annelida. Hau-FoxA3 is expressed during the morphogenesis of segmental ganglia from the ectodermal teloblast lineages, a clitellate-specific trait. Hau-FoxA1 and Hau-FoxA2 are also expressed during the morphogenesis of the leech-specific front sucker. CONCLUSIONS: The expression patterns suggested that Hau-FoxA1 carries out most of the conserved function in the endoderm and gut development, while the other two duplicates appear to have evolved unique novel functions in the directly developing clitellate embryos. Therefore, neofunctionalization and co-option of FoxA might have made a significant contribution to the evolution of direct development in Clitellata. Developmental Dynamics 247:763-778, 2018. © 2018 Wiley Periodicals, Inc.

Investigation of endoderm marker-genes during gastrulation and gut-development in the velvet worm Euperipatoides kanangrensis.

The ancestral state of animal gastrulation and its bearing for our understanding of bilaterian evolution still is one of the most controversially discussed topics in the field of evolutionary and developmental biology. One hypothesis, the so-called amphistomy scenario, suggests the presence of a slit-like blastopore in the last common ancestor of Bilateria. Onychophoran ontogeny at least superficially appears to support this scenario since a ventral groove clearly forms during gastrulation. The origin and nature of this groove, however, is another matter of ongoing controversy; i.e. the question of whether this structure actually represents the blastopore, or at least part of it. Recent research using genetic markers argued against the furrow representing a blastoporal structure. Here we investigate the origin of endoderm, which usually originates from the blastopore. We find conserved expression patterns of the endoderm- and gut-marker genes GATA456, GATA123, Hnf4 and fkh during gut development, and discuss the formation of the onychophoran gut in comparison with that in a range of arthropods. Despite expression of endodermal markers in and around the furrow we do not find convincing evidence that the furrow may be part of the blastopore, and thus we suggest that onychophoran development does not yield support for the amphistomy scenario.

Enteric neural crest cells regulate vertebrate stomach patterning and differentiation.

In vertebrates, the digestive tract develops from a uniform structure where reciprocal epithelial-mesenchymal interactions pattern this complex organ into regions with specific morphologies and functions. Concomitant with these early patterning events, the primitive GI tract is colonized by the vagal enteric neural crest cells (vENCCs), a population of cells that will give rise to the enteric nervous system (ENS), the intrinsic innervation of the GI tract. The influence of vENCCs on early patterning and differentiation of the GI tract has never been evaluated. In this study, we report that a crucial number of vENCCs is required for proper chick stomach development, patterning and differentiation. We show that reducing the number of vENCCs by performing vENCC ablations induces sustained activation of the BMP and Notch pathways in the stomach mesenchyme and impairs smooth muscle development. A reduction in vENCCs also leads to the transdifferentiation of the stomach into a stomach-intestinal mixed phenotype. In addition, sustained Notch signaling activity in the stomach mesenchyme phenocopies the defects observed in vENCC-ablated stomachs, indicating that inhibition of the Notch signaling pathway is essential for stomach patterning and differentiation. Finally, we report that a crucial number of vENCCs is also required for maintenance of stomach identity and differentiation through inhibition of the Notch signaling pathway. Altogether, our data reveal that, through the regulation of mesenchyme identity, vENCCs act as a new mediator in the mesenchymal-epithelial interactions that control stomach development.

The Vital Dye CDr10b Labels the Zebrafish Mid-Intestine and Lumen.

We describe the use of the fluorescent reporter compound CDr10b to label mid-intestinal structures in zebrafish larvae after simple immersion. CDr10b is deposited into the gut where it initially fills the lumen and is excreted. Using laser-mediated injury of the intestine, we show that CDr10b provides a useful readout of the integrity and repair of the epithelial cell barrier. In addition, CDr10b specifically labels the absorptive mid-intestine segment that is analogous to the mammalian small intestine. By perturbing retinoic acid signaling, which regulates the size of the mid-intestine segment, we show that CDr10b is a valuable tool to rapidly assess developmental malformations of the intestine in live animals.