Truncated Cables1 causes agenesis of the corpus callosum in mice

Disruption of entire Cables2 locus leads to embryonic lethality by diminished Rps21 gene expression and enhanced p53 pathway

In vivo function of CDK5 and Abl enzyme substrate 2 (Cables2), belonging to the Cables protein family, is unknown. Here, we found that targeted disruption of the entire Cables2 locus (Cables2d) caused growth retardation and enhanced apoptosis at the gastrulation stage and then induced embryonic lethality in mice. Comparative transcriptome analysis revealed disruption of Cables2, 50% down-regulation of Rps21 abutting on the Cables2 locus, and up-regulation of p53-target genes in Cables2d gastrulas. We further revealed the lethality phenotype in Rps21-deleted mice and unexpectedly, the exon 1-deleted Cables2 mice survived. Interestingly, chimeric mice derived from Cables2d ESCs carrying exogenous Cables2 and tetraploid wild-type embryo overcame gastrulation. These results suggest that the diminished expression of Rps21 and the completed lack of Cables2 expression are intricately involved in the embryonic lethality via the p53 pathway. This study sheds light on the importance of Cables2 locus in mouse embryonic development.

Characterization of a bicistronic knock-in reporter mouse model for investigating the role of CABLES2 in vivo

Two members of the CDK5 and ABL enzyme substrate (CABLES) family, CABLES1 and CABLES2, share a highly homologous C-terminus. They interact and associate with cyclin-dependent kinase 3 (CDK3), CDK5, and c-ABL. CABLES1 mediates tumor suppression, regulates cell proliferation, and prevents protein degradation. Although Cables2 is ubiquitously expressed in adult mouse tissues at RNA level, the role of CABLES2 in vivo remains unknown. Here, we generated bicistronic Cables2 knock-in reporter mice that expressed CABLES2 tagged with 3×FLAG and 2A-mediated fluorescent reporter tdTomato. Cables2-3×FLAG-2A-tdTomato (Cables2Tom) mice confirmed the expression of Cables2 in various mouse tissues. Interestingly, high intensity of tdTomato fluorescence was observed in the brain, testis and ovary, especially in the corpus luteum. Furthermore, immunoprecipitation analysis using the brain and testis in Cables2Tom/Tom revealed interaction of CABLES2 with CDK5. Collectively, our new Cables2 knock-in reporter model will enable the comprehensive analysis of in vivo CABLES2 function.

Generation of bicistronic reporter knockin mice for visualizing germ layers

Knockout mouse models are commonly used in developmental biology to investigate the functions of specific genes, and the knowledge obtained in such models has yielded insights into the molecular mechanisms underlying developmental processes. Gastrulation is the most dynamic process in embryogenesis during which differentiation into three germ layers occurs. However, the functions of genes involved in gastrulation are not completely understood. One major reason for this is the technical difficulty of embryo analysis to understand germ layer location. We have generated three reporter mouse strains in which the germ layers are distinguished by different fluorescent reporters. Using CRISPR/Cas9 genome editing in mouse zygotes, the fluorescent reporter genes, EGFP, tdTomato, and TagBFP including 2A peptide sequences were knocked into the appropriate sites before the stop codon of the Sox17 (endoderm marker), Otx2 (ectoderm marker), and T (mesoderm marker) genes, respectively. Founder mice were successfully generated in the Sox17-2A-EGFP, Otx2-2A-tdTomato, and T-2A-TagBFP knockin reporter strains. Further, homozygous knockin mice of all strains appeared morphologically normal and were fertile. On stereomicroscopic analysis, fluorescent signals were detected in a germ layer-specific manner from heterozygous embryos at embryonic day (E) 6.5-8.5 in all strains, and were immunohistochemically demonstrated to match their respective germ layer-specific marker protein at E7.5. Taken together, these observations suggest that the Sox17-2A-EGFP, Otx2-2A-tdTomato, and T-2A-TagBFP knockin reporter mice may be useful for comprehensive analysis of gene function in germ layer formation.

Loss-of-function mutations in the CABLES1 gene are a novel cause of Cushing's disease

The CABLES1 cell cycle regulator participates in the adrenal-pituitary negative feedback, and its expression is reduced in corticotropinomas, pituitary tumors with a largely unexplained genetic basis. We investigated the presence of CABLES1 mutations/copy number variations (CNVs) and their associated clinical, histopathological and molecular features in patients with Cushing's disease (CD). Samples from 146 pediatric (118 germline DNA only/28 germline and tumor DNA) and 35 adult (tumor DNA) CD patients were screened for CABLES1 mutations. CNVs were assessed in 116 pediatric CD patients (87 germline DNA only/29 germline and tumor DNA). Four potentially pathogenic missense variants in CABLES1 were identified, two in young adults (c.532G > A, p.E178K and c.718C > T, p.L240F) and two in children (c.935G > A, p.G312D and c.1388A > G, and p.D463G) with CD; no CNVs were found. The four variants affected residues within or close to the predicted cyclin-dependent kinase-3 (CDK3)-binding region of the CABLES1 protein and impaired its ability to block cell growth in a mouse corticotropinoma cell line (AtT20/D16v-F2). The four patients had macroadenomas. We provide evidence for a role of CABLES1 as a novel pituitary tumor-predisposing gene. Its function might link two of the main molecular mechanisms altered in corticotropinomas: the cyclin-dependent kinase/cyclin group of cell cycle regulators and the epidermal growth factor receptor signaling pathway. Further studies are needed to assess the prevalence of CABLES1 mutations among patients with other types of pituitary adenomas and to elucidate the pituitary-specific functions of this gene.

The Emerging Role of Cables1 in Cancer and Other Diseases

Cdk5 and Abl enzyme substrate 1 (Cables1) is an adaptor protein that links cyclin-dependent kinase (Cdks) with nonreceptor tyrosine kinases and regulates the activity of Cdks by enhancing their Y15 phosphorylation. Emerging evidence also shows that Cables1 can interact with, for example, p53 family proteins, 14-3-3, and β-catenin, suggesting that Cables1 may be a signaling hub for the regulation of cell growth. Abnormal expression of Cables1 has been observed in multiple types of cancers and other diseases. In this review, we summarize the characteristics of Cables1 and highlight the molecular mechanisms through which Cables1 regulates the development of cancer and other diseases. Finally, we discuss future challenges in demonstrating the role and potential application of Cables1 in cancer and other diseases.

Peri-implantation lethality in mice carrying megabase-scale deletion on 5qc3.3 is caused by Exoc1 null mutation

We found a novel spontaneous mouse mutant with depigmentation in the ventral body, which we called White Spotting (WS) mouse. Genetic investigation revealed deletion of a > 1.2-Mb genomic region containing nine genes (Kit, Kdr, Srd5a3, Tmeme165, Clock, Pdcl2, Nmu, Exoc1, and Cep135). We designated this mutant allele Kit^WS. Interestingly, homozygous mutants (Kit^WS/WS) showed a peri-implantation lethal phenotype. Expression analyses of these nine genes in blastocysts suggested that Exoc1 was a prime candidate for this phenotype. We produced Exoc1 knockout mice, and the same peri-implantation lethal phenotype was seen in Exoc1^−/− embryos. In addition, the polygenic effect without Exoc1 was investigated in genome-edited Kit^WE mice carrying the Mb-scale deletion induced by the CRISPR/Cas9 system. As Kit^WE/WE embryos did not exhibit the abnormal phenotype, which was seen in Kit^WS/WS. We concluded that peri-implantation lethality in Kit^WS/WS was caused by a monogenic defect of Exoc1.