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PubMed2001

vhnf1, the MODY5 and familial GCKD-associated gene, regulates regional specification of the zebrafish gut, pronephros, and hindbrain.

Mutations in the homeobox gene vHnf1 are associated with human diseases MODY5 (maturity-onset diabetes of the young, type V) and familial GCKD (glomerulocystic kidney disease). In an insertional mutagenesis screen in zebrafish, we isolated mutant alleles of vhnf1. Phenotypes of these mutants include formation of kidney cysts, underdevelopment of the pancreas and the liver, and reduction in size of the otic vesicles. We show that these abnormalities arise from patterning defects during development. We further provide evidence that vhnf1 regulates the expression of key patterning genes for these organs. vhnf1 is required for the proper expression of pdx1 and shh (sonic hedgehog) in the gut endoderm, pax2 and wt1 in the pronephric primordial, and valentino (val) in the hindbrain. Complementary to the loss-of-function phenotypes, overexpression of vhnf1 induces expansion of the val expression domain in the hindbrain. We propose that vhnf1 controls development of multiple organs through regulating regional specification of organ primordia. The similarity between vhnf1-associated fish phenotypes and human symptoms suggests a correlation between developmental functions of vhnf1 and the molecular etiology of MODY5 and GCKD.

Amino Acid Sequence↗
PubMed2005

Cilia-driven fluid flow in the zebrafish pronephros, brain and Kupffer's vesicle is required for normal organogenesis.

Cilia, as motile and sensory organelles, have been implicated in normal development, as well as diseases including cystic kidney disease, hydrocephalus and situs inversus. In kidney epithelia, cilia are proposed to be non-motile sensory organelles, while in the mouse node, two cilia populations, motile and non-motile have been proposed to regulate situs. We show that cilia in the zebrafish larval kidney, the spinal cord and Kupffer's vesicle are motile, suggesting that fluid flow is a common feature of each of these organs. Disruption of cilia structure or motility resulted in pronephric cyst formation, hydrocephalus and left-right asymmetry defects. The data show that loss of fluid flow leads to fluid accumulation, which can account for organ distension pathologies in the kidney and brain. In Kupffer's vesicle, loss of flow is associated with loss of left-right patterning, indicating that the 'nodal flow' mechanism of generating situs is conserved in non-mammalian vertebrates.

Animals↗
PubMed1992

Primed allogeneic reactions to leukocytes and epithelial cells in the bicolor damselfish.

The studies presented here describe allogeneic reactions in the bicolor damselfish, Pomacentrus partitus, a tropical marine teleost. Damselfish were immunized twice at 2-week intervals either by placement of reciprocal allografts or with primary cultures of epithelial cells. Two weeks after the second immunization, recipient splenocytes were tested for alloreactivity toward donor and third-party pronephros cells. For those animals immunized with cultured cells, reactivity toward donor and third-party epithelial cells was also examined. Unprimed animals responded to allogeneic pronephros between days 8 and 10 (28 degrees C). Fish immunized with epithelial cells showed accelerated mixed leukocyte reactions, with optimal responses occurring between days 4 and 6. Moreover, responses to the immunogen preceded responses to donor pronephros tissue by 2 days, occurring on day 2 or day 4. In addition, primed responses were of significantly greater magnitude than primary reactions. Reactivity toward third-party pronephros tissue paralleled responses of naive animals, indicating the specificity of response. No reactivity toward epithelial cells was observed in the absence of immunization, suggesting that accessory cell functions of damselfish pronephros and epithelial cells differ.

Animals↗
PubMed2002

Annexin IV (Xanx-4) has a functional role in the formation of pronephric tubules.

Vertebrate kidney organogenesis is characterised by the successive formation of the pronephros, the mesonephros and the metanephros. The pronephros is the first to form and is the functional embryonic kidney of lower vertebrates; although it is vestigial in higher vertebrates, it is a necessary precursor for the other kidney types. The Xenopus pronephros is a simple paired organ; each nephron consists of a single large glomus, one set of tubules and a single duct. The simple organisation of the pronephros and the amenability of Xenopus laevis embryos to manipulation make the Xenopus pronephros an attractive system in which to study organogenesis. It has been shown that pronephric tubules can be induced to form in presumptive ectodermal tissue by treatment with RA and activin. We have used this system in a subtractive hybridisation screen that resulted in the cloning of Xenopus laevis annexin IV (Xanx-4). Xanx-4 transcripts are specifically located to the developing pronephric tubules, and the protein to the luminal surface of these tubules. Temporal expression shows zygotic transcription is upregulated at the time of pronephric tubule specification and persists throughout pronephric development. The temporal and spatial expression pattern of Xanx-4 suggests it may have a role in pronephric tubule development. Overexpression of Xanx-4 yields no apparent phenotype, but Xanx-4 depletion, using morpholinos, produces a shortened, enlarged tubule phenotype. The phenotype observed can be rescued by co-injection of Xanx-4 mRNA. Although the function of annexins is not yet clear, studies have suggested a role for annexins in a number of cellular processes. Annexin IV has been shown to have an inhibitory role in the regulation of epithelial calcium-activated chloride ion conductance. The enlarged pronephric tubule phenotype observed may be attributed to incorrect modulation of exocytosis, membrane plasticity or ion channels and/or water homeostasis. In this study, we demonstrate an in vivo role for annexin IV in the development of the pronephric tubules in Xenopus laevis.

Amino Acid Sequence↗
PubMed1995

Development of the Xenopus pronephric system.

The pronephros serves as the embryonic kidney of the lower vertebrates. In this report we describe the development of the pronephric system of Xenopus laevis utilizing scanning electron microscopy and novel monoclonal antibodies that specifically recognize different parts of the pronephros. Antibody 3G8 recognizes the tubules and nephrostomes of the pronephroi only and does not react with the duct. Antibody 4A6 stains only the duct and the nephrostomes. These antibodies thus allow the positive identification of these two intermediate mesoderm derivatives. Both reagents detect antigens expressed some time after the pronephric structures first form and probably represent markers of terminal differentiation. When the tubules and duct first form they are separate structures that can easily be distinguished; the connective tubules have a distinctive organization, the collecting (or common) tubule is broader than other tubules, and the narrow pronephric duct has a specific shape and position. In later stages the collecting tubule and the rostral portion of the duct undergo a considerable amount of convolution, and both contribute to the final coiled tubular body of the pronephros. The ability of 3G8 and 4A6 to distinguish these two elements of the nephric system was used to reexplore classical experiments on the interaction between these two structures during development of the pronephric system. The use of whole-mount analysis has allowed us to examine large numbers of embryos from different stages and dissected in a variety of planes. These experiments demonstrate the dynamic nature of the intermediate mesoderm and indicate that although the pronephros may be specified by mid-neurula stages, patterning is not complete until tailbud stages.

Animals↗
PubMed2003

Chemiluminescence response of beta-glucan stimulated leukocytes isolated from different tissues and peritoneal cavity of Dicentrarchus labrax.

The respiratory burst of leukocytes isolated from sea bass (Dicentrarchus labrax) pronephros, peritoneal cavity (P.C.), spleen and blood, was measured by a chemiluminescence (CL) assay after stimulation with beta-glucan. The CL response by P.C. and pronephros leukocytes was significantly higher than that expressed by a similar number of cells separated from spleen and blood. This probably reflects the observation that the proportion of macrophages and neutrophils was highest in the populations of leukocytes from peritoneal cavity and pronephros. Comparative observations showed a higher degree of yeast phagocytosis by leukocytes taken from peritoneal cavity than the pronephros. Moreover phagocytic index evaluated by microscopical observations, indicated that peritoneal macrophages internalised more yeast cells than neutrophils (identified by the peroxidase reaction). Scanning electron microscopy observations were also carried out. Inhibition experiments by a myeloperoxidase inhibitor sodium azide, iodonium-diphenyl-chloride which inhibits NADPH-oxidase, and exogenous superoxide dismutase, which catalyses O-2 dismutation to H(2)O(2), supported the correlation between CL and respiratory burst. Treatment with ouabain and DNP suggested that in this response, Ca(++) pump channels and calmodulin are involved in a metabolic energy-dependent pathway.

Animals↗
PubMed1989

A cascading development model for amphibian embryos.

The mesodermal tissue of some amphibian gastrula develops into a dorsal-to-ventral sequence of notochord, somite, pronephros, and lateral plate cell types. The cellular proportions regulate with respect to embryo size. The dorsal blastoporal lip appears to function as an organizer for the embryo. The transplantation of a donor lip to the ventral side of a host causes a second, opposed embryo to form and the system commits similar total proportions of cells as do normally developing embryos. Transplantation of donor somite to the ventral side of a host causes a reduction in the proportion of host somite developed. A modified reaction-diffusion system governing embryo development is proposed. Developmental simulations consistent with experimental observations are presented and analyzed. The results suggest that the degree of somite inhibition is positively correlated with the size of the somite transplant. Further predictions are that sufficiently large somite transplants would induce ectopic, ventral pronephros to form and ventral pronephros transplants would inhibit host pronephros development.

Amphibians↗
PubMed2003

Identification and characterization of Xenopus NDRG1.

NDRG1 is a member of the N-myc downstream-regulated gene (NDRG) family and is involved in cellular differentiation, activation of p53, cell cycle arrest, metastasis, and hypoxia. Expression of NDRG1 is repressed by the proto-oncogene, N-myc during mouse development, although the exact functional role of NDRG1 in development remains unknown. Here, we report the characterization of Xenopus laevis NDRG1 (xNDRG1) during X. laevis development. Expression of xNDRG1 transcript was first detected at stage 15, and was localized to the presumptive pronephric anlagen at stage 26 and to pronephros, eye, branchial arches, and tail-bud at stage 32. Overexpression of xNDRG1 results in a reduced pronephros and disorganized somites. Depletion of xNDRG1, using morpholinos, causes failure of pronephros development. These results suggest that xNDRG1 is required for pronephros development in X. laevis.

Amino Acid Sequence↗