Laminins are heterotrimeric (α/β/γ) glycoproteins that form a major polymer within basement membranes. Different α, β and γ subunits can assemble into various laminin isoforms that have different, but often overlapping, distributions and functions. In this study, we examine the contributions of the laminin α subunits to the development of C. elegans. There are two α, one β and one γ laminin subunit, suggesting two laminin isoforms that differ by their α subunit assemble in C. elegans. We find that near the end of gastrulation and before other basement membrane components are detected, the α subunits are secreted between primary tissue layers and become distributed in different patterns to the surfaces of cells. Mutations in either α subunit gene cause missing or disrupted extracellular matrix where the protein normally localizes. Cell-cell adhesions are abnormal: in some cases essential cell-cell adhesions are lacking, while in other cases, cells inappropriately adhere to and invade neighboring tissues. Using electron microscopy, we observe adhesion complexes at improper cell surfaces and disoriented cytoskeletal filaments. Cells throughout the animal show defective differentiation, proliferation or migration, suggesting a general disruption of cell-cell signaling. The results suggest a receptor-mediated process localizes each secreted laminin to exposed cell surfaces and that laminin is crucial for organizing extracellular matrix, receptor and intracellular proteins at those surfaces. We propose this supramolecular architecture regulates adhesions and signaling between adjacent tissues.

Postnatal neovascularization is essential for wound healing, cancer progression, and many other physiological functions. However, its genetic mechanism is largely unknown. In this report, we study neovascularization in regenerating adult zebrafish fins using transgenic fish that express EGFP in blood vessel endothelial cells. We first describe the morphogenesis of regenerating vessels in wild-type animals and then the phenotypic analysis of a genetic mutation that disrupts blood vessel regeneration. In wild-type zebrafish caudal fins, amputated blood vessels heal their ends by 24 h postamputation (hpa) and then reconnect arteries and veins via anastomosis, to resume blood flow at wound sites by 48 hpa. The truncated vessels regenerate by first growing excess vessels to form unstructured plexuses, resembling the primary capillary plexuses formed during embryonic vasculogenesis. Interestingly, this mode of vessel growth switches by 8 days postamputation (dpa) to growth without a plexus intermediate. During blood vessel regeneration, vessel remodeling begins during early plexus formation and continues until the original vasculature pattern is reestablished at approximately 35 dpa. Temperature-sensitive mutants for reg6 have profound defects in blood vessel regeneration. At the restrictive temperature, reg6 regenerating blood vessels first fail to make reconnections between severed arteries and veins, and then form enlarged vascular sinuses rather than branched vascular plexuses. Reciprocal temperature-shift experiments show that reg6 function is required throughout plexus formation, but not during later growth. Our results suggest that the reg6 mutation causes defects in branch formation and/or angiogenic sprouting.

Aristolochic Acid (AA) is a component of Chinese herbs that has been found to be toxic to multiple organs in adults. Its toxicity to developing embryos has not been reported. Here, we describe that AA specifically causes heart defects in developing zebrafish embryos in a dosage-dependent manner. The treated embryos are able to develop their hearts normally up to 24 h postfertilization, when cardiac contraction initiates, but begin to show deformation and reduction of the hearts followed by gradual contractility loss and eventually lethality, suggesting that AA is primarily affecting cardiac physiology rather than cardiogenesis. Histological analyses reveal that the AA-treated hearts develop hypertrophy and disorganization of cardiomyocytes and loss of endocardium. By transmission electron microscopy, we observed broken and disorganized cardiac fibers in the AA-treated hearts. AA induces the expression of proinflammation genes, including cox-2, IL-1beta, and others. The AA-induced cardiac defects can be attenuated by the cox-2 antagonist NS398 via reducing the expression of the inflammatory genes. This attenuation could be further enhanced by known heart failure drugs, such as angiotensin-converting enzyme inhibitor and beta-adrenergic receptor antagonist. In contrast, the heart defects are enhanced by a beta-adrenergic receptor agonist. In summary, AA causes profound toxicity to zebrafish embryos that exhibit pathophysiological and pharmacological features resembling those of heart failure in humans and other model organisms, and thus, zebrafish could be a new model for studies on heart failure.

Capillary plexuses form during both vasculogenesis and angiogenesis and are remodeled into mature vessel types and patterns which are delicately orchestrated with the sizes and shapes of other tissues and organs. We isolated a zebrafish mutation named prp (for persistent plexus) that causes persistent formation of vascular plexuses in the caudal fins and consequent mispatterning of bony fin rays and the fin shape. Detailed analyses revealed that the prp mutation causes a significant reduction in the size and dramatic structural defects in collagen II-rich extracellular matrices called actinotrichia of both embryonic finfolds and adult fins. prp was mapped to chromosome 19 and found to encode the zebrafish collagen9α1 (col9α1) gene which is abundantly expressed in developing finfolds. A point mutation resulting in a leucine-to-histidine change was detected in the thrombospondin domain of the col9α1 gene in prp. Morpholino-mediated knockdown of col9α1 phenocopied the prp small-finfold phenotype in wild-type embryos, and an injection of plasmids containing the col9α1 cDNA into prp embryos locally restored the finfold size. Furthermore, we found that osteoblasts in prp mutants were mispatterned apparently following the abnormal vascular plexus pattern, demonstrating that blood vessels play an important role in the patterning of bony rays in zebrafish caudal fins.

Heart failure is a complex disease that involves genetic, environmental, and physiological factors. As a result, current medication and treatment for heart failure produces limited efficacy, and better medication is in demand. Although mammalian models exist, simple and low-cost models will be more beneficial for drug discovery and mechanistic studies of heart failure. We previously reported that aristolochic acid (AA) caused cardiac defects in zebrafish embryos that resemble heart failure. Here, we showed that cardiac troponin T and atrial natriuretic peptide were expressed at significantly higher levels in AA-treated embryos, presumably due to cardiac hypertrophy. In addition, several human heart failure drugs could moderately attenuate the AA-induced heart failure by 10%-40%, further verifying the model for drug discovery. We then developed a drug screening assay using the AA-treated zebrafish embryos and identified three compounds. Mitogen-activated protein kinase kinase inhibitor (MEK-I), an inhibitor for the MEK-1/2 known to be involved in cardiac hypertrophy and heart failure, showed nearly 60% heart failure attenuation. C25, a chalcone derivative, and A11, a phenolic compound, showed around 80% and 90% attenuation, respectively. Time course experiments revealed that, to obtain 50% efficacy, these compounds were required within different hours of AA treatment. Furthermore, quantitative polymerase chain reaction showed that C25, not MEK-I or A11, strongly suppressed inflammation. Finally, C25 and MEK-I, but not A11, could also rescue the doxorubicin-induced heart failure in zebrafish embryos. In summary, we have established two tractable heart failure models for drug discovery and three potential drugs have been identified that seem to attenuate heart failure by different mechanisms.