MOUSE MINUTES: A GENETIC STUDY OF RIBOSOMAL PROTEINS

描述（由申请人提供）：小鼠自发突变Bst（腹部斑点和尾巴）导致中腹侧斑点、椎体异常（尾巴打结）、轴前多指畸形、视网膜神经节细胞（RGC）数量减少、视神经发育不全、结肠瘤和视网膜下新生血管（Rice et al. 1997; Smith et al. 2000）。Bst纯合子在着床前死亡。我们已经确定Bst是Rpl24（编码大亚基核糖体蛋白L24的基因）中的缺失。该突变导致80%的转录本剪接异常，导致L24多肽截断。小鼠BAC和人cDNA转基因可纠正Bst/+表型。人们对脊椎动物的核糖体蛋白（RP）基因突变几乎一无所知。在果蝇中，许多被称为分钟的核糖体基因突变分散在整个基因组中（Lambertsson 1998）。它们是纯合子致死性的，具有类似的杂合子表型，包括更小、更薄的刚毛和严重延迟的发育（Schultz 1929）。它们的作用结合在一起时不是相加的。由于Minute细胞在体细胞嵌合体中与野生型克隆竞争较差，因此Minute细胞在定义细胞自主性、克隆谱系和发育区隔概念的开创性研究中发挥了重要作用（Simpson and Morata 1981）。在人类中，Diamond-Blackfan贫血（遗传性红细胞发育不全伴可变先天性异常）是由RPS19突变引起的，RPS19编码一个小亚基核蛋白（Willig et al. 1999）。鉴于细胞对核糖体的普遍需求，小鼠Rpl24和人类RPS19表型的组织特异性令人费解。我们的研究结果表明，核蛋白缺陷可能是常见的人类畸形综合征的基础，这些综合征疑似有遗传病因，但没有单一的靶位点（Lalani等，2003）。

DESCRIPTION (provided by applicant): The spontaneous mouse mutation Bst (belly spot and tail) causes midventral spotting, vertebral anomalies (tail kinks), preaxial polydactyly, a reduction in retinal ganglion cell (RGC) number, optic nerve aplasia, colobomata, and subretinal neovascularization (Rice et al. 1997; Smith et al. 2000). Bst homozygotes die before implantation. We have identified Bst as a deletion within Rpl24, the gene encoding the large subunit ribosomal protein L24. The mutation causes aberrant splicing in 80% of transcripts, leading to truncation of the L24 polypeptide. Mouse BAC and human cDNA transgenes correct the Bst/+ phenotype. Almost nothing is known about ribosomal protein (RP) gene mutations in vertebrates. In Drosophila, numerous ribosomal gene mutations, termed Minutes, are dispersed across the genome (Lambertsson 1998). They are homozygous lethal and have similar heterozygous phenotypes consisting of smaller, thinner bristles and profoundly delayed development (Schultz 1929). Their effects are not additive when combined. Minutes were instrumental in pioneering studies that defined concepts of cell autonomy, clonal lineage and developmental compartmentation, as Minute cells compete poorly with wild type clones in somatic mosaics (Simpson and Morata 1981). In humans, Diamond-Blackfan anemia (hereditary red blood cell aplasia with variable congenital anomalies) is caused by mutations in RPS19, which encodes a small subunit riboprotein (Willig et al. 1999). In view of the universal cellular requirement for ribosomes, the tissue specificity of mouse Rpl24 and human RPS19 phenotypes is puzzling. Our findings suggest that riboprotein defects may underlie common human malformation syndromes that have a suspected genetic etiology but no single target locus (Lalani et al. 2003). Fibroblasts from Bst/+ embryos grow slower than wild-type MEFs, remain longer in G1 phase, and exhibit decreased rates of protein synthesis. Although complete phenotypic surveys are lacking, the majority of tissues compensate for this cellular growth defect, so that organogenesis proceeds and Bst/+ mice approach normal adult size. While extraribosomal functions for L24 are possible, unique Bst phenotypes can also be explained by a dyschronic mechanism, in tissues such as the retina where proliferation and the sequence of cell fate determination are relatively uncoupled. In this proposal, we aim to: (1) complete characterization of Bst molecular, cellular and tissue developmental effects; (2) investigate the selective growth disadvantage of Rpl24 deficient cells in ROSA26 lacZ <-> Bst/+ blastocyst chimeras and somatic mosaics, as predicted by classical Minute studies; and (3) define the spectrum of riboprotein phenotypes by comparing Bst/+ mice to selected knockout mice with other RP mutations, including several that are available as targeted ES cells.