Deciphering arterial identity through gene expression, genetics, and chemical biology:

Dissection of cardiovascular development and disease pathways in zebrafish

The use of animal models in medicine has contributed significantly to the development of drug treatments and surgical procedures for the last century, in particular for cardiovascular disease. In order to model human disease in an animal, an appreciation of the strengths and limitations of the system are required to interpret results and design the logical sequence of steps toward clinical translation. As the world's population ages, cardiovascular disease will become even more prominent and further progress will be essential to stave off what seems destined to become a massive public health issue. Future treatments will require the imaginative application of current models as well as the generation of new ones. In this review, we discuss the resources available for modeling cardiovascular disease in zebrafish and the varied attributes of this system. We then discuss current zebrafish disease models and their potential that has yet to be exploited.

Zebrafish models for the functional genomics of neurogenetic disorders

In this review, we consider recent work using zebrafish to validate and study the functional consequences of mutations of human genes implicated in a broad range of degenerative and developmental disorders of the brain and spinal cord. Also we present technical considerations for those wishing to study their own genes of interest by taking advantage of this easily manipulated and clinically relevant model organism. Zebrafish permit mutational analyses of genetic function (gain or loss of function) and the rapid validation of human variants as pathological mutations. In particular, neural degeneration can be characterized at genetic, cellular, functional, and behavioral levels. Zebrafish have been used to knock down or express mutations in zebrafish homologs of human genes and to directly express human genes bearing mutations related to neurodegenerative disorders such as spinal muscular atrophy, ataxia, hereditary spastic paraplegia, amyotrophic lateral sclerosis (ALS), epilepsy, Huntington's disease, Parkinson's disease, fronto-temporal dementia, and Alzheimer's disease. More recently, we have been using zebrafish to validate mutations of synaptic genes discovered by large-scale genomic approaches in developmental disorders such as autism, schizophrenia, and non-syndromic mental retardation. Advances in zebrafish genetics such as multigenic analyses and chemical genetics now offer a unique potential for disease research. Thus, zebrafish hold much promise for advancing the functional genomics of human diseases, the understanding of the genetics and cell biology of degenerative and developmental disorders, and the discovery of therapeutics. This article is part of a Special Issue entitled Zebrafish Models of Neurological Diseases.

In the swim of things: recent insights to neurogenetic disorders from zebrafish

The advantage of zebrafish as a model to study human pathologies lies in the ease of manipulating gene expression in vivo. Here we focus on recent progress in our understanding of motor neuron diseases and neurodevelopmental disorders and discuss how novel technologies will permit further disease models to be developed. Together these advances set the stage for this simple functional model, with particular advantages for transgenesis, multigenic analyses and chemical biology, to become uniquely suited for advancing the functional genomics of neurological and possibly psychiatric diseases - from understanding the genetics and cell biology of degenerative and developmental disorders to the discovery of therapeutics.

Sp1 mediate hypoxia induced ephrinB2 expression via a hypoxia-inducible factor independent mechanism

Environmental factors are instrumental in maintaining a healthy vasculature. Oxygen tension is higher in arteries than in veins and thus has the potential to be an instructive signal in arterial/venous specification. EphrinB2 is specifically expressed in arteries and required during embryonic vessel formation. In this study, we show that expression of ephrinB2 is oxygen dependent. Mutagenesis of hypoxia-responsive elements and transactivation experiments determined this regulation to be achieved in a hypoxia-inducible factor independent manner. MAZ and Sp1 are known to regulate transcription together and have been shown to bind to the same sites within promoters. Chromatin immunoprecipitation confirmed that binding of Sp1 to the ephrinB2 promoter was favored compared to MAZ under hypoxic relative to normoxic conditions. Furthermore, siRNA mediated knockdown of Sp1 attenuated this hypoxic response. These results indicate that hypoxia drives arterial differentiation by increasing ephrinB2 expression in endothelial cells through Sp1 activation.

Zebrafish embryos as models for embryotoxic and teratological effects of chemicals

The experimental virtues of the zebrafish embryo such as small size, development outside of the mother, cheap maintenance of the adult made the zebrafish an excellent model for phenotypic genetic and more recently also chemical screens. The availability of a genome sequence and several thousand mutants and transgenic lines together with gene arrays and a broad spectrum of techniques to manipulate gene functions add further to the experimental strength of this model. Pioneering studies suggest that chemicals can have in many cases very similar toxicological and teratological effects in zebrafish embryos and humans. In certain areas such as cardiotoxicity, the zebrafish appears to outplay the traditional rodent models of toxicity testing. Several pilot projects used zebrafish embryos to identify new chemical entities with specific biological functions. In combination with the establishment of transgenic sensor lines and the further development of existing and new automated imaging systems, the zebrafish embryos could therefore be used as cost-effective and ethically acceptable animal models for drug screening as well as toxicity testing.

Role of crosstalk between phosphatidylinositol 3-kinase and extracellular signal-regulated kinase/mitogen-activated protein kinase pathways in artery-vein specification

Functional and structural differences between arteries and veins lie at the core of the circulatory system, both in health and disease. Therefore, understanding how artery and vein cell identities are established is a fundamental biological challenge with significant clinical implications. Molecular genetic studies in zebrafish and other vertebrates in the past decade have begun to reveal in detail the complex network of molecular pathways that specify artery and vein cell fates during embryonic development. Recently, a chemical genetic approach has revealed evidence that artery-vein specification is governed by cross talk between phosphoinositide 3-kinase and extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) signaling in artery-vein specification. We discuss recent findings on the signaling pathways involved in artery-vein specification during zebrafish development and compare and contrast these results to those from mammalian systems. It is anticipated that the complementary approaches of genetics and chemical biology, involving a variety of model organisms and systems, will lead to a better understanding of artery-vein specification and possibly to novel therapeutic approaches to treat vascular diseases.