Molecular cloning and knockdown of galactocerebrosidase in zebrafish: new insights into the pathogenesis of Krabbe's disease.

The lysosomal hydrolase galactocerebrosidase (GALC) catalyzes the removal of galactose from galactosylceramide and from other sphingolipids. GALC deficiency is responsible for globoid cell leukodystrophy (GLD), or Krabbe's disease, an early lethal inherited neurodegenerative disorder characterized by the accumulation of the neurotoxic metabolite psychosine in the central nervous system (CNS). The poor outcome of current clinical treatments calls for novel model systems to investigate the biological impact of GALC down-regulation and for the search of novel therapeutic strategies in GLD. Zebrafish (Danio rerio) represents an attractive vertebrate model for human diseases. Here, lysosomal GALC activity was demonstrated in the brain of zebrafish adults and embryos. Accordingly, we identified two GALC co-orthologs (named galca and galcb) dynamically co-expressed in CNS during zebrafish development. Both genes encode for lysosomal enzymes endowed with GALC activity. Single down-regulation of galca or galcb by specific antisense morpholino oligonucleotides results in a partial decrease of GALC activity in zebrafish embryos that was abrogated in double galca/galcb morphants. However, no psychosine accumulation was observed in galca/galcb double morphants. Nevertheless, double galca/galcb knockdown caused reduction and partial disorganization of the expression of the early neuronal marker neuroD and an increase of apoptotic events during CNS development. These observations provide new insights into the pathogenesis of GLD, indicating that GALC loss-of-function may have pathological consequences in developing CNS independent of psychosine accumulation. Also, they underscore the potentiality of the zebrafish system in studying the pathogenesis of lysosomal neurodegenerative diseases, including GLD.

Analysis of three µ1-AP1 subunits during zebrafish development.

BACKGROUND: The family of AP-1 complexes mediates protein sorting in the late secretory pathway and it is essential for the development of mammals. The ubiquitously expressed AP-1A complex consists of four adaptins γ1, ß1, µ1A, and σ1A. AP-1A mediates protein transport between the trans-Golgi network and early endosomes. The polarized epithelia AP-1B complex contains the µ1B-adaptin. AP-1B mediates specific transport of proteins from basolateral recycling endosomes to the basolateral plasma membrane of polarized epithelial cells. RESULTS: Analysis of the zebrafish genome revealed the existence of three µ1-adaptin genes, encoding µ1A, µ1B, and the novel isoform µ1C, which is not found in mammals. µ1C shows 80% sequence identity with µ1A and µ1B. The µ1C expression pattern largely overlaps with that of µ1A, while µ1B is expressed in epithelial cells. By knocking-down the synthesis of µ1A, µ1B and µ1C with antisense morpholino techniques we demonstrate that each of these µ1 adaptins is essential for zebrafish development, with µ1A and µ1C being involved in central nervous system development and µ1B in kidney, gut and liver formation. CONCLUSIONS: Zebrafish is unique in expressing three AP-1 complexes: AP-1A, AP-1B, and AP-1C. Our results demonstrate that they are not redundant and that each of them has specific functions, which cannot be fulfilled by one of the other isoforms. Each of the µ1 adaptins appears to mediate specific molecular mechanisms essential for early developmental processes, which depends on specific intracellular vesicular protein sorting pathways.

Zebrafish embryo as a tool to study tumor/endothelial cell cross-talk.

Tumor/endothelial cell cross-talk plays a pivotal role in the growth, neovascularization and metastatic dissemination of human cancer. Recent observations have shown that the teleost zebrafish (Danio rerio) may represent a powerful experimental platform in cancer research. Various tumor models have been established in zebrafish adults, juveniles, and embryos and novel genetic tools and high resolution in vivo imaging techniques have been exploited. In particular, grafting of mammalian tumor cells in zebrafish embryo body may simulate early stages of tumor development, neovascularization, and local invasion whereas the injection of cancer cells in the bloodstream of zebrafish embryo may allow the study of metastatic homing and colonization. This review focuses on the recent advances in tumor xenotransplantation in zebrafish embryo for the in vivo study of the cancer neovascularization, invasion and metastatic processes. This article is part of a Special Issue entitled: Animal Models of Disease.

In vitro and ex vivo retina angiogenesis assays.

Pathological angiogenesis of the retina is a key component of irreversible causes of blindness, as observed in proliferative diabetic retinopathy, age-related macular degeneration, and retinopathy of prematurity. Seminal studies in the early 1980 s about the angiogenic activity exerted by mammalian retinal tissue extracts on the chick embryo chorioallantoic membrane and the later discovery of vascular endothelial growth factor (VEGF) accumulation in eyes of patients with diabetic retinopathy paved the way for the development of anti-angiogenic VEGF blockers for the treatment of retinal neovascularization. Since then, numerous preclinical and clinical studies about diabetic retinopathy and other retinal disorders have opened new lines of angiogenesis inquiry, indicating that limitations to anti-VEGF therapies may exist. Moreover, the production of growth factors other than VEGF may affect the response to anti-VEGF approaches. Thus, experimental models of retinal angiogenesis remain crucial for investigating novel anti-angiogenic therapies and bringing them to patients. To this aim, in vitro and ex vivo angiogenesis assays may be suitable for a rapid screening of potential anti-angiogenic molecules before in vivo validation of the putative lead compounds. This review focuses on the different in vitro and ex vivo angiogenesis assays that have been developed over the years based on the isolation of endothelial cells from the retina of various animal species and ex vivo cultures of neonatal and adult retina explants. Also, recent observations have shown that eye neovascularization in zebrafish (Danio rerio) embryos, an in vivo animal platform experimentally analogous to in vitro/ex vivo models, may represent a novel target for the identification of angiogenesis inhibitors. When compared to in vivo assays, in vitro and ex vivo models of retina neovascularization, including zebrafish embryo, may represent cost-effective and rapid tools for the screening of novel anti-angiogenic therapeutics.

SIGMAR1 Regulates Membrane Electrical Activity in Response to Extracellular Matrix Stimulation to Drive Cancer Cell Invasiveness.

The sigma 1 receptor (Sig1R) is a stress-activated chaperone that regulates ion channels and is associated with pathologic conditions, such as stroke, neurodegenerative diseases, and addiction. Aberrant expression levels of ion channels and Sig1R have been detected in tumors and cancer cells, such as myeloid leukemia and colorectal cancer, but the link between ion channel regulation and Sig1R overexpression during malignancy has not been established. In this study, we found that Sig1R dynamically controls the membrane expression of the human voltage-dependent K(+) channel human ether-à-go-go-related gene (hERG) in myeloid leukemia and colorectal cancer cell lines. Sig1R promoted the formation of hERG/ß1-integrin signaling complexes upon extracellular matrix stimulation, triggering the activation of the PI3K/AKT pathway. Consequently, the presence of Sig1R in cancer cells increased motility and VEGF secretion. In vivo, Sig1R expression enhanced the aggressiveness of tumor cells by potentiating invasion and angiogenesis, leading to poor survival. Collectively, our findings highlight a novel function for Sig1R in mediating cross-talk between cancer cells and their microenvironment, thus driving oncogenesis by shaping cellular electrical activity in response to extracellular signals. Given the involvement of ion channels in promoting several hallmarks of cancer, our study also offers a potential strategy to therapeutically target ion channel function through Sig1R inhibition.

Zebrafish embryo intersegmental vessels: a tool for investigating sprouting angiogenesis.

Angiogenesis leads to the formation of the intersegmental vessels (ISVs) of the trunk in teleost zebrafish (Danio rerio) embryo. Here we describe experimental procedures, including in vivo observation of transgenic zebrafish embryo and whole mount in situ hybridization, to investigate ISV development in zebrafish embryos and assess the effect of antiangiogenic compounds on these vessels.