Fog1 is required for cardiac looping in zebrafish

Abstract

To further our understanding of FOG gene function during cardiac development, we utilized zebrafish to examine FOG's role in the early steps of heart morphogenesis. We identified fragments of three fog genes in the zebrafish genomic database and isolated full-length coding sequences for each of these genes by using a combination of RT-PCR and 5'-RACE. One gene was similar to murine FOG-1 (fog1), while the remaining two were similar to murine FOG-2 (fog2a and fog2b). All Fog proteins were able to physically interact with GATA4 and function as transcriptional co-repressors. Whole-mount in situ hybridization revealed fog1 expression in the heart, the hematopoietic system, and the brain, while fog2a and fog2b expression was restricted to the brain. Injection of zebrafish embryos with a morpholino directed against fog1 resulted in embryos with a large pericardial effusion and an unlooped heart tube. This looping defect could be rescued by co-injection of mRNA encoding murine FOG-1, but not by mRNA encoding FOG-1 lacking the FOG repression motif. Taken together, these results demonstrate the importance of FOG proteins for zebrafish cardiac development and suggest a previously unappreciated role for FOG proteins in heart looping that is dependent on the FOG repression motif.

Combinatorial regulation of tissue specification by GATA and FOG factors

“…The genome of Danio rerio has three FOG genes, including one ortholog of Fog1 and two of Fog2 (Fig. 1B) (Walton et al, 2006). Each zebrafish FOG protein has the same zinc finger structure as its mammalian ortholog, except that Fog1 contains an additional zinc finger between fingers 4 and 5 that appears to be marginally conserved in mouse FOG1.…”

“…Each zebrafish FOG protein has the same zinc finger structure as its mammalian ortholog, except that Fog1 contains an additional zinc finger between fingers 4 and 5 that appears to be marginally conserved in mouse FOG1. All three zebrafish FOG proteins possess the conserved NuRD and CtBP interaction domains and are capable of repressing a GATA4-dependent reporter (Walton et al, 2006). In developing zebrafish embryos, fog1 (zfpm1) is expressed in the heart, the nervous system and the inner cell mass (ICM), which is the site of hematopoiesis.…”

“…In developing zebrafish embryos, fog1 (zfpm1) is expressed in the heart, the nervous system and the inner cell mass (ICM), which is the site of hematopoiesis. fog2a and fog2b (zfpm2a and zfpm2b) expression is restricted to the developing brain (Walton et al, 2006), although nothing is known about their functions. Xenopus, however, has only one FOG homolog, xFOG, which is most similar to murine FOG1 (Fig.…”

An alternative transcript of the FOG-2 gene encodes a FOG-2 isoform lacking the FOG repression motif

“…This fragment was cloned into the Hind III/Kpn I site of pcDNA3 along with a Kpn I fragment encoding the remainder of the FOG-2S open reading frame and 3'-UTR. NIH 3T3 fibroblasts were cultured and transfected as previously described [23]. Primary cultures of neonatal rat cardiocytes were prepared as previously described [24] and plated onto Rat Tail Collagen I coated 12-well plates (Biocoat, Fisher Scientific, Waltham, MA).…”

“…Three days following transfection, cells and media were harvested and assayed for human growth hormone (hGH) expression, β-galactosidase activity, and protein concentration. Relative promoter activity was calculated by normalizing for transfection efficiency using β-galactosidase activity as previously described [23].…”