The understanding of cause and pathogenesis of many complex human diseases has been improved through the study of model organisms. Zebrafish are a well-established model used to study developmental biology because of their accessibility, optical transparency and rapid development. Over the past decade, the utility of this model organism in investigations of human health and disease has become more explicit. Major advantages of this vertebrate model include a high degree of homology to human genes, as well as conservation of developmental pathways. Zebrafish chd7 gene is located on chromosome 2 and alignment of the zebrafish genomic sequence with mouse Chd7 and human CHD7 shows the gene structure is conserved across species [18]. Given that the zebrafish chd7 gene is highly similar to the human CHD7 gene, elucidating roles for Chd7 in zebrafish development could significantly contribute to our understanding of the function of Chd7 in CHARGE syndrome pathogenesis. Therefore, we sought to utilize zebrafish to assess the pathogenic effect of the loss of function of Chd7 and understand the role of the zebrafish homolog of the mammalian Chd7 during development. We show that chd7 is robustly expressed in developing zebrafish embryos, particularly in the retina, hindbrain and tail bud. Loss of function of Chd7 results in several defects including abnormal neural development, curvature of the long axis of the body, abnormal cranial neural crest (CNC) development, otolith anomalies, smaller eye and pericardial edema. These defects are similar to the major congenital anomalies associated with human CHD7 mutations in Role of Chd7 in Developing Zebrafish CHARGE syndrome. Finally, we reveal for the first time a critical role of Chd7 in retinal organization and bone mineralization. Results Chd7 transcript is broadly expressed in developing zebrafish To begin to explore the role of Chd7 in developing zebrafish, we first analyzed the developmental expression of chd7 mRNA. In situ hybridization results showed that chd7 was expressed relatively ubiquitously throughout early zebrafish embryogenesis (Fig. 1 A–C) until around the 13 somite stage of development when more discrete expression in the eye primordium, and the perimeter of the somites was observed (Fig. 1 D). As somitogenesis continued, chd7 became highly expressed in the retina as well as in the brain, somites, and tailbud of the embryo (Fig. 1 E–F). Finally at 48 hpf, chd7 expression in the tail began to diminish, however expression in the brain and in the eye remained strong (Fig. 1 G). The sense probe did not show any in situ staining suggesting that there was no non-specific hybridization (Fig. 1 E9). Loss of function of Chd7 leads to several and widespread morphological abnormalities Next, we depleted zebrafish embryos of Chd7 protein using an antisense morpholino oligonucleotide (MO) designed against the translation initiation sites of chd7 mRNA. Embryos injected with Figure 1. Chd7 expression patterns during zebrafish embryogenesis. Chd7 was expressed ubiquitously throughout the embryo during epiboly (A), at the 4 somite stage (B), and at the 8 somite stage (C). (D) At the 13 somite stage, expression remained relatively ubiquitous, but with stronger expression noted within the retina and at the perimeters of developed somites. (E) At the 18 somite stage, tissue-specific expression was observed in the eyes, brain, somites, and tailbud. This expression pattern remained through 24 hours post fertilization (F). (E9) No staining occurred when hybridized with a chd7 sense probe. (G) At 48 hours post fertilization, chd7 expression began to diminish from the body of the zebrafish but remained in the eye and in the brain. e, eye; ep, eye primordium; mb, midbrain; hp, head primordium; s, somite; t, tail; tb, tailbud; y, yolk; ye, yolk extension. doi:10.1371/journal.pone.0031650.g001 PLoS ONE | www.plosone.org 2 February 2012 | Volume 7 | Issue 2 | e31650