A modifier screen identifies DNAJB6 as a cardiomyopathy susceptibility gene

Gene-environment interactions in birth defect etiology: Challenges and opportunities

Birth defects are relatively common congenital outcomes that significantly impact affected individuals, their families, and communities. Effective development and deployment of prevention and therapeutic strategies for these conditions requires sufficient understanding of etiology, including underlying genetic and environmental causes. Tremendous progress has been made in defining the genetic basis of familial and syndromic forms of birth defects. However, the majority of birth defect cases are considered nonsyndromic and thought to result from multifactorial gene-environment interactions. While substantial advances have been made in elucidating the genetic landscape of these etiologically complex conditions, significant biological and technical constraints have stymied progress toward a refined knowledge of environmental risk factors. Defining specific gene-environment interactions in birth defect etiology is even more challenging. However, progress has been made, including demonstration of critical proofs of concept and development of new conceptual and technical approaches for resolving complex gene-environment interactions. In this review, we discuss current views of multifactorial birth defect etiology, comparing them with other diseases that also involve gene-environment interactions, including primary immunodeficiency and cancer. We describe how various model systems have illuminated mechanisms of multifactorial etiology and these models' individual strengths and weaknesses. Finally, suggestions for areas of future emphasis are proposed.

Building the vertebrate codex using the gene breaking protein trap library

One key bottleneck in understanding the human genome is the relative under-characterization of 90% of protein coding regions. We report a collection of 1200 transgenic zebrafish strains made with the gene-break transposon (GBT) protein trap to simultaneously report and reversibly knockdown the tagged genes. Protein trap-associated mRFP expression shows previously undocumented expression of 35% and 90% of cloned genes at 2 and 4 days post-fertilization, respectively. Further, investigated alleles regularly show 99% gene-specific mRNA knockdown. Homozygous GBT animals in ryr1b, fras1, tnnt2a, edar and hmcn1 phenocopied established mutants. 204 cloned lines trapped diverse proteins, including 64 orthologs of human disease-associated genes with 40 as potential new disease models. Severely reduced skeletal muscle Ca²⁺ transients in GBT ryr1b homozygous animals validated the ability to explore molecular mechanisms of genetic diseases. This GBT system facilitates novel functional genome annotation towards understanding cellular and molecular underpinnings of vertebrate biology and human disease.

Using Zebrafish to Analyze the Genetic and Environmental Etiologies of Congenital Heart Defects

Congenital heart defects (CHDs) are among the most common human birth defects. However, the etiology of a large proportion of CHDs remains undefined. Studies identifying the molecular and cellular mechanisms that underlie cardiac development have been critical to elucidating the origin of CHDs. Building upon this knowledge to understand the pathogenesis of CHDs requires examining how genetic or environmental stress changes normal cardiac development. Due to strong molecular conservation to humans and unique technical advantages, studies using zebrafish have elucidated both fundamental principles of cardiac development and have been used to create cardiac disease models. In this chapter we examine the unique toolset available to zebrafish researchers and how those tools are used to interrogate the genetic and environmental contributions to CHDs.

LGMD1D myopathy with cytoplasmic and nuclear inclusions in a Saudi family due to DNAJB6 mutation

Autosomal dominant LGMD1D has been described in multiple families in Asia, Europe, and USA. However, to the best of our knowledge, no cases of LGMD1D have been reported among native Bedouin Saudi families. Fifty Saudi families with LGMD were analyzed and the causative underlying genes were studied utilizing genome wide linkage, homozygosity mapping, and neurological gene panel. We identified one family of a Bedouin origin with LGMD1D. Two patients had progressive proximal and distal weakness, dysphagia, and respiratory symptoms. Creatinine kinase was normal. Muscle biopsy showed marked variation in myofibers size with scattered angular atrophic fiber, necrotic fibers, and myophagocytosis, with red-rimmed vacuoles depicting a sarcoplasmic body. Heterozygous c.C287T (p.P96L) variant in exon 5 of DNAJB6 (NM_005494) gene was found. This change is localized within glycine and phenylalanine rich domain and alter an amino acid residue. Our findings will expand on the existing genotypic and phenotypic spectrum of this disorder and aid in elucidating hidden mechanisms implicated in LGMD1D.

A Doxorubicin-induced Cardiomyopathy Model in Adult Zebrafish

The genetically accessible adult zebrafish (Danio rerio) has been increasingly used as a vertebrate model for understanding human diseases such as cardiomyopathy. Because of its convenience and amenability to high throughput genetic manipulations, the generation of acquired cardiomyopathy models, such as the doxorubicin-induced cardiomyopathy (DIC) model in adult zebrafish, is opening the doors to new research avenues, including discovering cardiomyopathy modifiers via forward genetic screening. Different from the embryonic zebrafish DIC model, both initial acute and later chronic phases of cardiomyopathy can be determined in the adult zebrafish DIC model, enabling the study of stage-dependent signaling mechanisms and therapeutic strategies. However, variable results can be obtained with the current model, even in the hands of experienced investigators. To facilitate future implementation of the DIC model, we present a detailed protocol on how to generate this DIC model in adult zebrafish and describe two alternative ways of intraperitoneal (IP) injection. We further discuss options on how to reduce variations to obtain reliable results and provide suggestions on how to appropriately interpret the results.