Femoral bone structure and mechanics at the edge and core of an expanding population of the invasive frog Xenopus laevis.

Understanding how living tissues respond to changes in their mechanical environment is a key question in evolutionary biology. Invasive species provide an ideal model for this as they are often transplanted between environments that differ drastically in their ecological and environmental context. Spatial sorting, the name given to the phenomenon driving differences between individuals at the core and edge of an expanding range, has been demonstrated to impact the morphology and physiology of Xenopus laevis from the invasive French population. Here, we combined a structural analysis using micro-CT scanning and a functional analysis by testing the mechanical properties of the femur to test whether the increased dispersal at the range edge drives differences in bone morphology and function. Our results show significant differences in the inner structure of the femur as well as bone material properties, with frogs from the centre of the range having more robust and resistant bones. This is suggestive of an energy allocation trade-off between locomotion and investment in bone formation, or alternatively, may point to selection for fast locomotion at the range edge. Overall, our results provide insights on the growth of the long bones and the formation of trabecular bone in frogs.

Ocular microvasculature in adult Xenopus laevis: Scanning electron microscopy of vascular casts.

The microvascular anatomy of choriocapillaris, iris, ciliary body, and superficial vascular hyaloid system of eyes was studied in the permanent aquatic Xenopus laevis by scanning electron microscopy of vascular casts and was compared with that published in two semiaquatic ranid species (Rana esculenta and Rana temporaria), and the urodelian species Triturus criststus carnifex. Results showed that the choriocapillaris in Xenopus consisted of a dense meshwork of wide capillaries displaying polygonal arrays at the scleral side with venules leaving the centers and arterioles supplied from the periphery. The choriocapillaris lacked the multilayered capillary meshwork described in ranids. Iris and ciliary body were supplied by nasal and temporal branches of the iridial artery, which either originated with a common stem from the hyaloid artery or arose as individual vessels from the proximal portions of the semicircular nasal and temporal branches of the hyaloid artery. These branches ran in the pupillary margin and supplied the two-dimensional capillary network of the iris, as well as the three-dimensional network of the ciliary body. Iris and ciliary body drained via parallel running vasa recta into the choriocapillaris. The superficial vascular hyaloid bed (system) was supplied by the hyaloid artery. This artery coursed along the scleral surface of the ventrotemporal choriocapillaris toward the ora serrata, where it bifurcated into a temporal and a nasal semicircular branch. Seven to 10 arterial meridional twigs arose from these branches and supplied the superficial hyaloid capillary bed. Capillaries drained into branches of the hyaloid vein, which ascended toward the ora serrata, where the hyaloid vein joined the temporal branch of the ciliary vein.

A cellular platform for the development of synthetic living machines.

Robot swarms have, to date, been constructed from artificial materials. Motile biological constructs have been created from muscle cells grown on precisely shaped scaffolds. However, the exploitation of emergent self-organization and functional plasticity into a self-directed living machine has remained a major challenge. We report here a method for generation of in vitro biological robots from frog (Xenopus laevis) cells. These xenobots exhibit coordinated locomotion via cilia present on their surface. These cilia arise through normal tissue patterning and do not require complicated construction methods or genomic editing, making production amenable to high-throughput projects. The biological robots arise by cellular self-organization and do not require scaffolds or microprinting; the amphibian cells are highly amenable to surgical, genetic, chemical, and optical stimulation during the self-assembly process. We show that the xenobots can navigate aqueous environments in diverse ways, heal after damage, and show emergent group behaviors. We constructed a computational model to predict useful collective behaviors that can be elicited from a xenobot swarm. In addition, we provide proof of principle for a writable molecular memory using a photoconvertible protein that can record exposure to a specific wavelength of light. Together, these results introduce a platform that can be used to study many aspects of self-assembly, swarm behavior, and synthetic bioengineering, as well as provide versatile, soft-body living machines for numerous practical applications in biomedicine and the environment.

Microvascular anatomy of the urinary bladder in the adult African clawed toad, Xenopus laevis: A scanning electron microscope study of vascular casts.

We studied urinary bladders of adult male and female Xenopus laevis using light microscopy of stained tissue sections and scanning electron microscopy (SEM) of vascular corrosion casts (VCCs). Results showed that bilaterally a vesical artery branched off the femoral artery. At the dorso-lateral serosal surface of the body of the bladder each artery splitted within a short distance into up to five smaller arteries that supplied body and neck regions. Arteries gave off short and long terminal arterioles, which fed the mucosal capillary meshwork. Long terminal arterioles followed dimensional changes of the bladder, while short ones anchored the capillary network to the arterial system. Capillary mesh sizes and shapes varied according to the filling state of the urinary bladder. In the highly to moderately distended (filled) bladder, capillaries were rather straight or undulated only slightly, in the contracted (emptied) bladder they undulated strongly and lay side by side. Postcapillary venules formed by two equally sized capillaries or from capillaries, which serially drained into a small postcapillary venule. Vesical venules formed a large dorsal vesical and a varying number of smaller lateral and ventral vesical veins. The dorsal vesical vein drained either directly or via the posterior hemorrhoidal vein into the common pelvic vein. Lateral and ventral vesical veins also drained into the latter. The vascular patterns found were discussed in respect to the bladder spatial movements during distention (filling) and relaxation (emptying). Furthermore, it was hypothesized that an extensively filled bladder could compress the overlaying abdominal vein forcing part of the blood otherwise drained towards the liver to be detoured via the renal portal veins to the kidneys.

Microvascular anatomy of ovary and oviduct in the adult African Clawed Toad (Xenopus laevis DAUDIN, 1802)-Histomorphology and scanning electron microscopy of vascular corrosion casts.

Ovaries and oviducts of the adult African Clawed Toad (Xenopus laevis DAUDIN, 1802) were studied by light microscopy (LM) of paraplast embedded tissue sections and scanning electron microscopy (SEM) of vascular corrosion casts (VCCs). Histomorphology revealed that ovarian vessels located in the thecal layers. Ovarian and interlobar arteries displayed a horse-shoe shaped longitudinally running bundle of vascular smooth muscle cells. Follicular blood vessels showed flattened profiles, which were confirmed by scanning electron microscopy in vascular corrosion casts. The flattened profiles obviously led to high intravasal pressures, which locally prevented filling of the follicular capillary bed. Oviduct arteries pierced the fibrous stroma surrounding the oviduct mucosa. In the pars convoluta, the mucosa consisted of a ciliated simple columnar epithelium and tubular oviduct glands that opened between ciliated epithelial cells into the oviduct lumen. Oviduct arteries branched at the basolateral surfaces of tubular glands. After a short tangential course, arterioles branched into capillaries which ran radially between oviduct glands towards the subepithelium. Anastomoses at different heights connected capillaries of neighbouring glands. Subepithelially, capillaries ran longitudinally and undulated. Postcapillary venules radiated centrifugally towards the stroma to finally drain into oviduct veins located in the stroma. Oviduct vascular densities clearly reflected non-ovulatory and ovulatory states.

Allocation trade-offs impact organ size and muscle architecture in an invasive population of Xenopus laevis in Western France.

Invasive species are a global scourge and often negatively impact native species. Understanding the expansion and dispersal limits of these species is essential. As previous studies have demonstrated increased locomotor performance for populations at the edge of the range of expanding populations, studies of locomotion including the anatomical and physiological traits underlying dispersal capacity are of interest. We focus here on an invasive population of Xenopus laevis introduced in France nearly forty years ago. Previous studies have demonstrated differences in mobility between populations from the centre and the edge of the invasive range, with individuals from the range edge possessing a higher endurance capacity. We test here whether range-edge frogs show anatomical differences in organs or muscles underlying these observed differences of performance. We dissected 10 males and 10 females from central and range-edge sites (40 animals in total) and measured the mass of their organs and the mass, the length, and the physiological cross-sectional area (PCSA) of 28 hind limb muscles. Our results show anatomical differences with individuals from the range edge possessing heavier, longer and more forceful muscles. Moreover, females from the range edge had a heavier heart but lighter stomach than those of the centre of the range. Future studies comparing the morphology between native and invasive populations in other regions or for other species will be especially insightful to better understand the possible adaptive changes in invasive populations and the limits on dispersal capacity.

Modeling underwater hearing and sound localization in the frog Xenopus laevis.

Animals that are small compared to sound wavelengths face the challenge of localizing a sound source since the main cues to sound direction-interaural time differences (ITD) and interaural level differences (ILD)-both depend on size. Remarkably, the majority of terrestrial vertebrates possess internally coupled ears (ICE) with an air-filled cavity connecting the two eardrums and producing an inherently directional middle-ear system. Underwater, longer wavelengths and faster sound-speed reduce both ITD and ILD cues. Nonetheless, many animals communicate through and localize underwater sound. Here, a typical representative equipped with ICE is studied: the fully aquatic clawed frog Xenopus laevis. It is shown that two factors improve underwater sound-localization quality. First, inflated lungs function as Helmholtz resonator and generate directional amplitude differences between eardrum vibrations in the high-frequency (1.7-2.2 kHz) and low-frequency (0.8-1.2 kHz) range of the male advertisement calls. Though the externally arriving ILDs practically vanish, the perceived internal level differences are appreciable, more than 10 dB. As opposed to, e.g., lizards with thin and flexible eardrums, plate-like eardrums are shown to be Xenopus' second key to successfully handling aquatic surroundings. Based on ICE, both plate-like eardrums and inflated lungs functioning as Helmholtz resonators explain the phonotaxis performance of Xenopus.

Investigating the function and possible biological role of an acetylcholine-gated chloride channel subunit (ACC-1) from the parasitic nematode Haemonchus contortus.

The cys-loop superfamily of ligand-gated ion channels are well recognized as important drug targets for many invertebrate specific compounds. With the rise in resistance seen worldwide to existing anthelmintics, novel drug targets must be identified so new treatments can be developed. The acetylcholine-gated chloride channel (ACC) family is a unique family of cholinergic receptors that have been shown, using Caenorhabditis elegans as a model, to have potential as anti-parasitic drug targets. However, there is little known about the function of these receptors in parasitic nematodes. Here, we have identified an acc gene (hco-acc-1) from the sheep parasitic nematode Haemonchus contortus. While similar in sequence to the previously characterized C. elegans ACC-1 receptor, Hco-ACC-1 does not form a functional homomeric channel in Xenopus oocytes. Instead, co-expression of Hco-ACC-1 with a previously characterized subunit Hco-ACC-2 produced a functional heteromeric channel which was 3x more sensitive to acetylcholine compared to the Hco-ACC-2 homomeric channel. We have also found that Hco-ACC-1 can be functionally expressed in C. elegans. Overexpression of both cel-acc-1 and hco-acc-1 in both C. elegans N2 and acc-1 null mutants decreased the time for worms to initiate reversal avoidance to octanol. Moreover, antibodies were generated against the Hco-ACC-1 protein for use in immunolocalization studies. Hco-ACC-1 consistently localized to the anterior half of the pharynx, specifically in pharyngeal muscle tissue in H. contortus. On the other hand, expression of Hco-ACC-1 in C. elegans was restricted to neuronal tissue. Overall, this research has provided new insight into the potential role of ACC receptors in parasitic nematodes.

Microvascular anatomy of olfactory and accessory olfactory (vomeronasal) organs in adult Xenopus laevis: scanning electron microscopy of vascular corrosion casts / Anatomía microvascular de órganos olfatorios y accesorios (vomeronasal) en adultos Xenopus laevis: microscopía electrónica de barrido de moldes de corrosión vascular

Microvascular anatomy and histomorphology of olfactory and vomeronasal organs in adult Xenopus laevis Daudin were studied by scanning electron microscopy of vascular corrosion casts and paraplast embedded stained serial tissue sections. Results show that the arterial supply is bilaterally by terminal arterioles of the medial branch of the nasal artery and by the palatal artery. Arterioles give rise to a capillary meshwork characteristic for respiratory surfaces in principal chambers and in dorsal and caudal areas of middle chambers. Anterior and inferior areas of the middle chambers own a distinctly different capillary network with conspicuous short capillary loops. Loops have a dilated tip and extend in acute angles towards the chamber lumen. The vomeronasal organ (VNO) locates beneath the olfactory organ. It has a medial to lateral extension and attaches with its caudal circumference to the medial nasal glands. Its capillary bed displays rectangular meshes which preferentially orientate along the long axis of the VNO. Locally, capillaries form short hairpin-like or strongly twisted loops with dilated tips which point towards the lumen of the VNO. These capillaries slow-down blood velocity and may lead to an increased exchange of oxygen, nutrients and water-borne odorants in the middle chambers and of pheromones in the VNO. In the latter vascular structures are present which might serve as a vascular pump.

Se estudiaron la anatomía microvascular e histomorfología de los órganos olfatorios y vomeronasales de Xenopus laevis Daudin adultos, mediante microscopía electrónica de barrido de moldes de corrosión vascular y secciones de tejido seriadas, teñidas e incluídas en paraplast. Los resultados muestran que el suministro arterial es bilateral por arteriolas terminales de la rama medial de la arteria nasal y por la arteria palatina. Las arteriolas dan lugar a un lecho capilar característico de las superficies respiratorias en las cámaras principales y en las áreas dorsal y caudal de las cámaras intermedias. Las áreas anterior e inferior de las cámaras centrales poseen una red capilar significativamente diferente con llamativos bucles capilares cortos. Los bucles tienen una punta dilatada y se extienden en ángulos agudos hacia la luz de la cámara. El órgano vomeronasal (VNO) se ubica debajo del órgano olfatorio. Se extiende de medial a lateral y se une con su circunferencia caudal a las glándulas nasales mediales. El lecho capilar muestra mallas rectangulares que se orientan preferentemente a lo largo del eje longitudinal del VNO. Localmente, los capilares forman bucles cortos en forma de horquilla o fuertemente retorcidos con puntas dilatadas que apuntan hacia la luz del VNO. Estos capilares ralentizan la velocidad de la sangre y pueden conducir a un mayor intercambio de oxígeno, nutrientes y odorizantes, a base de agua en las cámaras intermedias y de feromonas, en el VNO. En este último, están presentes estructuras vasculares que podrían servir como una bomba vascular.

A rapid and nondestructive protocol for whole-mount bone staining of small fish and Xenopus.

Here we propose a new protocol for whole-mount bone staining, which allows the rapid preparation of highly cleared and nondestructive specimens. It only takes 3 days to complete whole procedure for small vertebrates, such as medaka, zebrafish, and Xenopus frogs. In this procedure, we used a newly developed fixative containing formalin, Triton X-100, and potassium hydroxide, which allows the fixation, decolorization, and transparentization of specimens at the same time. A bone staining solution containing alizarin red S with ethylene glycol and a clearing solution containing Tween 20 and potassium hydroxide also contributed the specificity and swiftness of this new system. As expected, although details of the skeletal system could be observed in specimens with high transparency, it was noteworthy that high-resolution fluorescence images acquired using zoom microscopes clearly delineated the shape of each bone. This new procedure would be expected to be widely used as a standard procedure for bone staining in the testing the developmental toxicity of chemicals and in the screening test of knockout or mutant animals.

Fluorescent Anesthetics.

Methods for using exogenous fluorophore and general anesthetic 1-aminoanthracene (1-AMA) and its photoactive derivative 1-azidoanthracene (1-AZA) are provided. 1-AMA potentiates GABAA chloride currents and immobilizes Xenopus laevis tadpoles. Cellular and tissue anesthetic distribution can be imaged for quantifying "on-pathway" and "off-pathway" targets. 1-AZA shares targets with 1-AMA and offers further optoanesthetic spatial and temporal control upon near-UV laser irradiation. Furthermore, 1-AZA adduction provides screening of possible relevant anesthetic protein targets and binding site characterization. We highlight several useful imaging and binding assays to demonstrate utility of 1-AMA and its derivative 1-AZA.

Microvascular anatomy of the brain of the adult pipid frog, Xenopus laevis (Daudin): A scanning electron microscopic study of vascular corrosion casts.

To demonstrate the 3D microvascular anatomy of the brain of the model organism Xenopus laevis Daudin scanning electron microscopy of vascular corrosion casts was correlated with light microscopy of stained 7 µm thick serial tissues sections. Results showed that supplying arteries descended from the leptomeningeal surface without remarkable branchings straight to the subventricular zone where they branched and capillarized. Capillaries showed few H- and/or Y-shaped anastomoses during their centrifugal course toward the leptomeningeal surface where they drained into cerebral venules and veins. Apart from the accessory olfactory bulb and the vestibule-cochlear nucleus where capillaries were densely packed, capillaries formed a wide-meshed 3D network throughout the brain parenchyma and thus contrasted to urodelian brains where hairpin-shaped capillaries descend from the leptomeningeal vessels into varying depths of the brain parenchyma. In about two-third of specimens, a closed arterial circle of Willis was found at the base of the brain. If this circle in Xenopus might serve the same two functions as in men is briefly discussed. Choroid plexuses of third and fourth ventricle were found to have a high venous, but a low arterial inflow via one small choroidal artery only. Findings are compared with previous studies on the vascularization of the anuran brain and discrepancies in respect to presence or absence of particular arteries and/or veins in Ranids, Bufonids, and Pipids studied so far are discussed with particular emphasis on the techniques used in the various studies published so far.

Cellular composition and organization of the spinal cord central canal during metamorphosis of the frog Xenopus laevis.

Studying the cellular composition and morphological changes of cells lining the central canal during Xenopus laevis metamorphosis could contribute to understand postnatal development and spinal cord regeneration. Here we report the analysis of central canal cells at different stages during metamorphosis using immunofluorescence for protein markers expression, transmission and scanning electron microscopy and cell proliferation assays. The central canal was regionalized according to expression of glial markers, ultrastructure, and proliferation in dorsal, lateral, and ventral domains with differences between larvae and froglets. In regenerative larvae, all cell types were uniciliated, have a radial morphology, and elongated nuclei with lax chromatin, resembling radial glial cells. Important differences in cells of nonregenerative froglets were observed, although uniciliated cells were found, the most abundant cells had multicilia and revealed extensive changes in the maturation and differentiation state. The majority of dividing cells in larvae corresponded to uniciliated cells at dorsal and lateral domains in a cervical-lumbar gradient, correlating with undifferentiated features. Neurons contacting the lumen of the central canal were detected in both stages and revealed extensive changes in the maturation and differentiation state. However, in froglets a very low proportion of cells incorporate 5-ethynyl-2'-deoxyuridine (EdU), associated with the differentiated profile and with the increase of multiciliated cells. Our work showed progressive changes in the cell types lining the central canal of Xenopus laevis spinal cord which are correlated with the regenerative capacities.

Muscarinic modulation of the Xenopus laevis tadpole spinal mechanosensory pathway.

Muscarinic acetylcholine receptors (mAChRs) mediate effects of acetylcholine (ACh) in many systems, including those involved in spinal functions like locomotion. In Xenopus laevis tadpoles at two days old, a model vertebrate for motor control research, we investigated the role of mAChRs in the skin mechanosensory pathway. We found that mAChR activation by carbachol did not affect the sensory Rohon-Beard neuron properties. However, carbachol could hyperpolarise sensory interneurons and decrease their voltage responses to outward currents. Carbachol could increase the threshold for the mechanosensory pathway to start swimming, preventing the initiation of swimming at higher concentrations altogether. Recording from the sensory interneurons in carbachol showed that their spiking after skin stimulation was depressed. However, the general muscarinic antagonist atropine did not have a clear effect on the swimming threshold or the modulation of sensory interneuron membrane conductance. Our results suggest the skin mechanosensory pathway may be subject to muscarinic modulation in this simple vertebrate system.

Sequence and timing of early cranial skeletal development in Xenopus laevis.

Xenopus laevis is widely used as a model organism in biological research. Morphological descriptions of the larval cartilaginous skeleton are more than half a century old and comprehensive studies of early cartilage differentiation and development are missing. A proper understanding of early cranial skeletal development in X. laevis requires a detailed description that can function as a baseline for experimental studies. This basis makes it possible to evaluate skeletal defects produced by experiments on gene interactions, such as gain- or loss-of function experiments. In this study, we provide a detailed description of the pattern and timing of early cartilage differentiation and development in the larval head of X. laevis. Methods used include antibody staining, confocal laser scanning microscopy and 3D-reconstruction. Results were than compared to earlier studies based on classical histological approaches and clearing-and-staining. The first cartilage to chondrify is, in contrast to other vertebrates investigated so far, the ceratohyal. The components of the branchial basket chondrify in anterior-to-posterior direction as reported for other amphibians. Chondrification of different cartilages begins at different stages and the majority of cartilages are fully developed at Ziermann and Olsson stage 17. Our baseline data on the pattern and timing of early cartilaginous development in X. laevis is useful for evaluation of experiments which alter head skeletal development as well as for identifying heterochronic shifts in head development in other amphibians.

Three-dimensional reconstruction of the cranial and anterior spinal nerves in early tadpoles of Xenopus laevis (Pipidae, Anura).

Xenopus laevis is one of the most widely used model organism in neurobiology. It is therefore surprising, that no detailed and complete description of the cranial nerves exists for this species. Using classical histological sectioning in combination with fluorescent whole mount antibody staining and micro-computed tomography we prepared a detailed innervation map and a freely-rotatable three-dimensional (3D) model of the cranial nerves and anterior-most spinal nerves of early X. laevis tadpoles. Our results confirm earlier descriptions of the pre-otic cranial nerves and present the first detailed description of the post-otic cranial nerves. Tracing the innervation, we found two previously undescribed head muscles (the processo-articularis and diaphragmatico-branchialis muscles) in X. laevis. Data on the cranial nerve morphology of tadpoles are scarce, and only one other species (Discoglossus pictus) has been described in great detail. A comparison of Xenopus and Discoglossus reveals a relatively conserved pattern of the post-otic and a more variable morphology of the pre-otic cranial nerves. Furthermore, the innervation map and the 3D models presented here can serve as an easily accessible basis to identify alterations of the innervation produced by experimental studies such as genetic gain- and loss of function experiments.

Wall following in Xenopus laevis is barrier-driven.

The tendency of animals to follow boundaries within their environment can serve as a strategy for spatial learning or defensive behaviour. We examined whether Xenopus laevis tadpoles and froglets employ such a strategy by characterizing their swimming pattern in a square tank with shallow water. Trajectories obtained from video recordings were analysed for proximity to the nearest wall. With the exception of young larvae, the vast majority of animals (both tadpoles and froglets) spent a disproportionately large amount of time near the wall. The total distance covered was not a confounding factor, but animals were stronger wall followers in smaller tanks. Wall following was also not influenced by whether the surrounding walls of the tank were black or white, illuminated by infrared light, or by the presence or absence of tentacles. When given a choice in a convex tank to swim straight and leave the wall or turn to follow the wall, the animals consistently left the wall, indicating that wall following in X. laevis is barrier-driven. This implies that wall following behaviour in Xenopus derives from constraints imposed by the environment (or the experimenter) and is unlikely a strategy for spatial learning or safety seeking.

Studying the role of axon fasciculation during development in a computational model of the Xenopus tadpole spinal cord.

During nervous system development growing axons can interact with each other, for example by adhering together in order to produce bundles (fasciculation). How does such axon-axon interaction affect the resulting axonal trajectories, and what are the possible benefits of this process in terms of network function? In this paper we study these questions by adapting an existing computational model of the development of neurons in the Xenopus tadpole spinal cord to include interactions between axons. We demonstrate that even relatively weak attraction causes bundles to appear, while if axons weakly repulse each other their trajectories diverge such that they fill the available space. We show how fasciculation can help to ensure axons grow in the correct location for proper network formation when normal growth barriers contain gaps, and use a functional spiking model to show that fasciculation allows the network to generate reliable swimming behaviour even when overall synapse counts are artificially lowered. Although we study fasciculation in one particular organism, our approach to modelling axon growth is general and can be widely applied to study other nervous systems.

Digital dissection of the model organism Xenopus laevis using contrast-enhanced computed tomography.

The African clawed frog, Xenopus laevis, is one of the most widely used model organisms in biological research. However, the most recent anatomical description of X. laevis was produced nearly a century ago. Compared with other anurans, pipid frogs - including X. laevis - exhibit numerous unusual morphological features; thus, anatomical descriptions of more 'typical' frogs do not detail many aspects of X. laevis skeletal and soft-tissue morphology. The relatively new method of using iodine-based agents to stain soft tissues prior to high-resolution X-ray imaging has several advantages over gross dissection, such as enabling dissection of very small and fragile specimens, and preserving the three-dimensional topology of anatomical structures. Here, we use contrast-enhanced computed tomography to produce a high-resolution three-dimensional digital dissection of a post-metamorphic X. laevis to successfully visualize: skeletal and muscular anatomy; the nervous, respiratory, digestive, excretory and reproductive systems; and the major sense organs. Our digital dissection updates and supplements previous anatomical descriptions of this key model organism, and we present the three-dimensional data as interactive portable document format (PDF) files that are easily accessible and freely available for research and educational purposes. The data presented here hold enormous potential for applications beyond descriptive purposes, particularly for biological researchers using this taxon as a model organism, comparative anatomy and biomechanical modelling.

Upregulation of matrix metalloproteinase triggers transdifferentiation of retinal pigmented epithelial cells in Xenopus laevis: A Link between inflammatory response and regeneration.

In adult Xenopus eyes, when the whole retina is removed, retinal pigmented epithelial (RPE) cells become activated to be retinal stem cells and regenerate the whole retina. In the present study, using a tissue culture model, it was examined whether upregulation of matrix metalloproteinases (Mmps) triggers retinal regeneration. Soon after retinal removal, Xmmp9 and Xmmp18 were strongly upregulated in the tissues of the RPE and the choroid. In the culture, Mmp expression in the RPE cells corresponded with their migration from the choroid. A potent MMP inhibitor, 1,10-PNTL, suppressed RPE cell migration, proliferation, and formation of an epithelial structure in vitro. The mechanism involved in upregulation of Mmps was further investigated. After retinal removal, inflammatory cytokine genes, IL-1ß and TNF-α, were upregulated both in vivo and in vitro. When the inflammation inhibitors dexamethasone or Withaferin A were applied in vitro, RPE cell migration was severely affected, suppressing transdifferentiation. These results demonstrate that Mmps play a pivotal role in retinal regeneration, and suggest that inflammatory cytokines trigger Mmp upregulation, indicating a direct link between the inflammatory reaction and retinal regeneration. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1086-1100, 2017.