[Show abstract][Hide abstract] ABSTRACT: Pitx genes play important roles in a variety of developmental processes in vertebrates. In an ascidian species, Halocynthia roretzi, Hr-Pitx, the only Pitx gene of this species, has been reported to be expressed in the left epidermis at the tailbud stage. In the present study, first, we have shown that Hr-Pitx is also expressed in the papilla-forming region at the neurula to tailbud stages, and then we addressed transcription regulatory mechanisms for the expression of Hr-Pitx in the papilla-forming region. We have identified the genomic region ranging from 850 to 1211 bp upstream from the translation start site of the Hr-Pitx gene as an enhancer region that drives the transcription of Hr-Pitx in the papilla-forming region. Within the enhancer region, putative transcriptional factor binding sites for Otx as well as Fox were shown to be required for its activity. Finally, we carried out knocking down experiments of Hr-Otx function using an antisense morpholino oligonucleotide, in which the knocking down of Hr-Otx function resulted in reduction of the enhancer activity and loss of the expression of Hr-Pitx in the papilla-forming region. In Xenopus laevis, it has been reported that Pitx genes are expressed downstream of Otx function during development of the cement gland, an adhesive organ of its larva. Taken together, it is suggested that the expression regulatory mechanism of Pitx, involving Otx as the upstream gene, in the developing adhesive organ is conserved between ascidians and vertebrates.
[Show abstract][Hide abstract] ABSTRACT: Nodal signaling plays an essential role in the establishment of left-right asymmetry in various animals. However, it is largely unknown how Nodal signaling is involved in the establishment of the left-right asymmetric morphology. In this study, the role of Nodal signaling in the left-right asymmetric ocellus formation in the ascidian, Ciona intestinalis was dealt with. During the development of C. intestinalis, the ocellus pigment cell forms on the midline and moves to the right side of the midline. Then, the photoreceptor cells form on the right side of the sensory vesicle (SV). Ci-Nodal is expressed on the left side of the SV in the developing tail bud embryo. When Nodal signaling is inhibited, the ocellus pigment cell form but remain on the midline, and expression of marker genes of the ocellus photoreceptor cells is ectopically detected on the left side as well as on the right side of the SV in the larva. Furthermore, Ci-Rx, which is essential for the ocellus differentiation, turns out to be negatively regulated by the Nodal signaling on the left side of the SV, even though it is required for the right-sided photoreceptor formation. These results indicate that Nodal signaling controls the left-right asymmetric ocellus formation in the development of C. intestinalis.
[Show abstract][Hide abstract] ABSTRACT: Left-right asymmetric expression of Pitx as well as of Nodal has been observed in some ascidian species, but a mechanism that regulates the asymmetric expression of Pitx remains largely unclear. We addressed the transcription regulatory mechanism of the left-right asymmetric expression of Pitx gene in the ascidian, Ciona intestinalis. We first identified an intronic enhancer that drives Ci-Pitx left-sided expression in the epidermis and found that a single FoxH1 binding site present in this enhancer is essential for its activity. Also, we have shown that the enhancer requires Nodal signaling to drive the Ci-Pitx expression in the left epidermis. In C. intestinalis, left-sided expression of the Nodal gene has not been reported so far. We have confirmed that Ci-Nodal is expressed in the left epidermis of embryos at the tailbud stage only when they are allowed to develop within the chorion. Then, to test the importance of the FoxH1 binding site, we carried out knock down experiments using morpholino antisense oligonucleotides against Ci-FoxHa, the only FoxH gene that is expressed in the same stage as the left-sided expression of Ci-Pitx is observed. Knocking down of the function of Ci-FoxHa led to the down regulation of the expression of Ci-Pitx in the left epidermis. The present results suggest that the regulatory mechanism controlling the left-right asymmetric expression of the Pitx genes is well conserved between C. intestinalis and vertebrates.
Development Genes and Evolution 08/2008; 218(7):353-60. · 2.18 Impact Factor