Loss of Ribosomal Protein L11 Affects Zebrafish Embryonic Development through a p53-Dependent Apoptotic Response

Ribosome is responsible for protein synthesis in all organisms and ribosomal proteins (RPs) play important roles in the formation of a functional ribosome. L11 was recently shown to regulate p53 activity through a direct binding with MDM2 and abrogating the MDM2-induced p53 degradation in response to ribosomal stress. However, the studies were performed in cell lines and the significance of this tumor suppressor function of L11 has yet to be explored in animal models. To investigate the effects of the deletion of L11 and its physiological relevance to p53 activity, we knocked down the rpl11 gene in zebrafish and analyzed the p53 response. Contrary to the cell line-based results, our data indicate that an L11 deficiency in a model organism activates the p53 pathway. The L11-deficient embryos (morphants) displayed developmental abnormalities primarily in the brain, leading to embryonic lethality within 6–7 days post fertilization. Extensive apoptosis was observed in the head region of the morphants, thus correlating the morphological defects with apparent cell death. A decrease in total abundance of genes involved in neural patterning of the brain was observed in the morphants, suggesting a reduction in neural progenitor cells. Upregulation of the genes involved in the p53 pathway were observed in the morphants. Simultaneous knockdown of the p53 gene rescued the developmental defects and apoptosis in the morphants. These results suggest that ribosomal dysfunction due to the loss of L11 activates a p53-dependent checkpoint response to prevent improper embryonic development

Foxf2: A Novel Locus for Anterior Segment Dysgenesis Adjacent to the Foxc1 Gene

Anterior segment dysgenesis (ASD) is characterised by an abnormal migration of neural crest cells or an aberrant differentiation of the mesenchymal cells during the formation of the eye's anterior segment. These abnormalities result in multiple tissue defects affecting the iris, cornea and drainage structures of the iridocorneal angle including the ciliary body, trabecular meshwork and Schlemm's canal. In some cases, abnormal ASD development leads to glaucoma, which is usually associated with increased intraocular pressure. Haploinsufficiency through mutation or chromosomal deletion of the human FOXC1 transcription factor gene or duplications of the 6p25 region is associated with a spectrum of ocular abnormalities including ASD. However, mapping data and phenotype analysis of human deletions suggests that an additional locus for this condition may be present in the same chromosomal region as FOXC1. DHPLC screening of ENU mutagenised mouse archival tissue revealed five novel mouse Foxf2 mutations. Re-derivation of one of these (the Foxf2W174R mouse lineage) resulted in heterozygote mice that exhibited thinning of the iris stroma, hyperplasia of the trabecular meshwork, small or absent Schlemm's canal and a reduction in the iridocorneal angle. Homozygous E18.5 mice showed absence of ciliary body projections, demonstrating a critical role for Foxf2 in the developing eye. These data provide evidence that the Foxf2 gene, separated from Foxc1 by less than 70 kb of genomic sequence (250 kb in human DNA), may explain human abnormalities in some cases of ASD where FOXC1 has been excluded genetically

Whole-exome sequencing of congenital glaucoma patients reveals hypermorphic variants in GPATCH3, a new gene involved in ocular and craniofacial development

Congenital glaucoma (CG) is a heterogeneous, inherited and severe optical neuropathy that originates from maldevelopment of the anterior segment of the eye. To identify new disease genes, we performed whole-exome sequencing of 26 unrelated CG patients. In one patient we identified two rare, recessive and hypermorphic coding variants in GPATCH3, a gene of unidentified function, and 5% of a second group of 170 unrelated CG patients carried rare variants in this gene. The recombinant GPATCH3 protein activated in vitro the proximal promoter of CXCR4, a gene involved in embryo neural crest cell migration. The GPATCH3 protein was detected in human tissues relevant to glaucoma (e.g., ciliary body). This gene was expressed in the dermis, skeletal muscles, periocular mesenchymal-like cells and corneal endothelium of early zebrafish embryos. Morpholino-mediated knockdown and transient overexpression of gpatch3 led to varying degrees of goniodysgenesis and ocular and craniofacial abnormalities, recapitulating some of the features of zebrafish embryos deficient in the glaucoma-related genes pitx2 and foxc1. In conclusion, our data suggest the existence of high genetic heterogeneity in CG and provide evidence for the role of GPATCH3 in this disease. We also show that GPATCH3 is a new gene involved in ocular and craniofacial development.This study has been supported by research grants from the “Instituto de Salud Carlos III/FEDER” (RD12/0034/0003, PI11/00662, PI15/01193 to JE and CP12/03256 to MC), the Ministry of Economy and Competitiveness/FEDER (MINECO, SAF2013-46943-R to MC and PT13/0001/0044 to MG), Mutua Madrileña Foundation (to MC), and the Regional Ministry of Science and Technology of the Board of the Communities of “Castilla-La Mancha” (PEII-2014-002-P to JE). Jesús-José Ferre-Fernández is the recipient of a predoctoral fellowship from the “Instituto de Salud Carlos III” (FI12/00287). Miguel Coca-Prados is “Catedrático Rafael del Pino en Oftalmología” in the “Fundación de Investigación Oftalmológica, Instituto Oftalmológico Fernández-Vega” Oviedo, Spain. Marta Corton is sponsored by the Miguel Servet Program (CP12/03256) from Instituto de Salud Carlos III/FEDER)

Ribosomes

Ribosomes are fundamental components of the cell that are essential for its growth and proliferation. It is hard to imagine that such a fundamental physiological machinery, as ribosomes, does not participate in cancer biology. However, surprisingly, there is a lack of studies towards the role of ribosomal alterations in cancer. Here, we will attempt to summarize current knowledge regarding the link between the ribosomal machinery and human cancer. Various malfunctions in ribosomal activity represented by defects in ribosome biogenesis have been associated with human disease. Recent studies performed both in yeast and in higher eukaryotes have linked various aspects of ribosome biogenesis to the control of cell growth and proliferation. It is now clear that disruption of ribosome biogenesis is a cause of several inherited genetic disorders that have been associated with an increased risk of tumor development. In this chapter we discuss some recent insights into the mechanisms by which alterations in ribosome biogenesis contribute to the biology of cancer