Peter Pan functions independently of its role in ribosome biogenesis during early eye and craniofacial cartilage development in Xenopus laevis.

The Xenopus oocyte possesses a large maternal store of ribosomes, thereby uncoupling early development from the de novo ribosome biosynthesis required for cell growth. Brix domain-containing proteins, such as Peter Pan (PPan), are essential for eukaryotic ribosome biogenesis. In this study, we demonstrate that PPan is expressed maternally as well as in the eye and cranial neural crest cells (NCCs) during early Xenopus laevis development. Depletion of PPan and interference with rRNA processing using antisense morpholino oligonucleotides resulted in eye and cranial cartilage malformations. Loss of PPan, but not interference with rRNA processing, led to an early downregulation of specific marker genes of the eye, including Rx1 and Pax6, and of NCCs, such as Twist, Slug and FoxD3. We found that PPan protein is localized in the nucleoli and mitochondria and that loss of PPan results in increased apoptosis. These findings indicate a novel function of PPan that is independent of its role in ribosome biogenesis.

Pescadillo homologue 1 and Peter Pan function during Xenopus laevis pronephros development.

BACKGROUND INFORMATION: pes1 (pescadillo homologue 1) and ppan (Peter Pan) are multifunctional proteins involved in ribosome biogenesis, cell proliferation, apoptosis, cell migration and regulation of gene expression. Both proteins are required for early neural development in Xenopus laevis, as previously demonstrated. RESULTS: We show that the expression of both genes in the developing pronephros depends on wnt4 and fzd3 (frizzled homologue 3) function. Loss of pes1 or ppan by MO (morpholino oligonucleotide)-based knockdown approaches resulted in strong malformations during pronephric tubule formation. Defects were already notable during specification of pronephric progenitor cells, as shown by lhx1 expression. Moreover, we demonstrated that Xenopus pes1 and ppan interact physically and functionally and that pes1 and ppan can cross-rescue the loss of function phenotype of one another. Interference with rRNA synthesis, however, did not result in a similar early pronephros phenotype. CONCLUSION: These results demonstrate that pes1 and ppan are required for Xenopus pronephros development and indicate that their function in the pronephros is independent of their role in ribosome biosynthesis.

Xenopus laevis insulin receptor substrate IRS-1 is important for eye development.

Extracellular signal transduction into cells through ligand-activated receptor tyrosine kinases, such as insulin-like growth factor-1 (IGF-1) receptor (IGF-1R) and insulin receptor (IR) is required for normal embryonic growth and development. The major mediators of IR and IGF-1R are adaptor proteins of the insulin receptor substrate family, the best characterized member of which is IRS-1. Insulin receptor substrate IRS-1 has been shown to influence cell and body size and to interfere with differentiation. We have isolated IRS-1 from Xenopus laevis embryos and analyzed for the first time its spatial and temporal expression pattern during embryogenesis. We found that Xenopus IRS-1 is expressed maternally and constantly during embryogenesis. It is predominantly found in neural tissue at different stages. Furthermore, knock down of IRS-1 in neural tissue by specific antisense morpholino oligonucleotides (MO) resulted in abnormal eye formation accompanied by reduction of the eye-specific marker genes Rx1 and Pax6 and a decreased cell proliferation.

FMR1/FXR1 and the miRNA pathway are required for eye and neural crest development.

FMR1 and FXR1 are RNA binding proteins interacting with the miRNA-induced silencing complex, RISC. Here we describe for the first time the function of these proteins during eye and neural crest (NC) development in Xenopus laevis. A loss of FMR1 or FXR1 results in abnormal eye development as well as defects in cranial cartilage derived from cranial NC cells. We further investigated the possible mechanism of these phenotypes by showing that a depletion of Dicer, an important enzyme for generating all mature miRNAs, in the anterior neural tissue also leads to eye and cranial cartilage defects. Furthermore, we examined the function of 12 miRNAs during anterior neural development. We show a specific requirement of six selected miRNAs during eye and cranial cartilage development. Mir-130a, -219, and -23b are involved in eye formation only whereas loss of miR-200b, miR-96 and miR-196a results in strong defects during eye as well as cranial cartilage development. Our results suggest an essential role for FMR1 and FXR1 for eye and NC development in X.laevis likely through an interaction with the miRNA pathway.

Targeting self-renewal in high-grade brain tumors leads to loss of brain tumor stem cells and prolonged survival.

Cancer stem cells (CSCs) have been suggested as potential therapeutic targets for treating malignant tumors, but the in vivo supporting evidence is still missing. Using a GFP reporter driven by the promoter of the nuclear receptor tailless (Tlx), we demonstrate that Tlx(+) cells in primary brain tumors are mostly quiescent. Lineage tracing demonstrates that single Tlx(+) cells can self-renew and generate Tlx(-) tumor cells in primary tumors, suggesting that they are brain tumor stem cells (BTSCs). After introducing a BTSC-specific knock-out of the Tlx gene in primary mouse tumors, we observed a loss of self-renewal of BTSCs and prolongation of animal survival, accompanied by induction of essential signaling pathways mediating cell-cycle arrest, cell death, and neural differentiation. Our study demonstrates the feasibility of targeting glioblastomas and indicates the suitability of BTSCs as therapeutic targets, thereby supporting the CSC hypothesis.