Citations

Significance Statement Zebrafish embryos are well recognized for their value in studying polycystic kidney disease, but they cannot fully recapitulate the pathogenesis of the disease. The establishment of tmem67 e3/e3 mutants provides the first adult zebrafish model for cystogenesis. The model exhibits progressive renal cysts and enables the discernment of compensational effects from pathogenic events. Development of a tissue-clearing, whole-mount imaging protocol allows the analysis of renal cysts and cilia abnormality at a single-nephron resolution. Evidence also indicates potential benefit of mammalian target of rapamycin inhibition in tmem67 -based cystogenesis. Combining powerful genetics and phenotyping tools, this novel adult zebrafish model shall facilitate mechanistic studies and therapeutic development for cystic diseases. Background Although zebrafish embryos have been used to study ciliogenesis and model polycystic kidney disease (PKD), adult zebrafish remain unexplored. Methods Transcription activator-like effector nucleases (TALEN) technology was used to generate mutant for tmem67 , the homolog of the mammalian causative gene for Meckel syndrome type 3 (MKS3). Classic 2D and optical-clearing 3D imaging of an isolated adult zebrafish kidney were used to examine cystic and ciliary phenotypes. A hypomorphic mtor strain or rapamycin was used to inhibit mTOR activity. Results Adult tmem67 zebrafish developed progressive mesonephric cysts that share conserved features of mammalian cystogenesis, including a switch of cyst origin with age and an increase in proliferation of cyst-lining epithelial cells. The mutants had shorter and fewer distal single cilia and greater numbers of multiciliated cells (MCCs). Absence of a single cilium preceded cystogenesis, and expansion of MCCs occurred after pronephric cyst formation and was inversely correlated with the severity of renal cysts in young adult zebrafish, suggesting a primary defect and an adaptive action, respectively. Finally, the mutants exhibited hyperactive mTOR signaling. mTOR inhibition ameliorated renal cysts in both the embryonic and adult zebrafish models; however, it only rescued ciliary abnormalities in the adult mutants. Conclusions Adult zebrafish tmem67 mutants offer a new vertebrate model for renal cystic diseases, in which cilia morphology can be analyzed at a single-nephron resolution and mTOR inhibition proves to be a candidate therapeutic strategy.

Abstract Splicing alterations are common in diseases such as cancer, where mutations in splicing factor genes are frequently responsible for aberrant splicing. Here we present an alternative mechanism for splicing regulation in T-cell acute lymphoblastic leukemia (T-ALL) that involves posttranslational stabilization of the splicing machinery via deubiquitination. We demonstrate there are extensive exon skipping changes in disease, affecting proteasomal subunits, cell-cycle regulators, and the RNA machinery. We present that the serine/arginine-rich splicing factors (SRSF), controlling exon skipping, are critical for leukemia cell survival. The ubiquitin-specific peptidase 7 (USP7) regulates SRSF6 protein levels via active deubiquitination, and USP7 inhibition alters the exon skipping pattern and blocks T-ALL growth. The splicing inhibitor H3B-8800 affects splicing of proteasomal transcripts and proteasome activity and acts synergistically with proteasome inhibitors in inhibiting T-ALL growth. Our study provides the proof-of-principle for regulation of splicing factors via deubiquitination and suggests new therapeutic modalities in T-ALL. Significance: Our study provides a new proof-of-principle for posttranslational regulation of splicing factors independently of mutations in aggressive T-cell leukemia. It further suggests a new drug combination of splicing and proteasomal inhibitors, a concept that might apply to other diseases with or without mutations affecting the splicing machinery. This article is highlighted in the In This Issue feature, p. 1241

RXRA is an endothelial- and early stage–predominant therapeutic target for treating anthracycline-induced cardiotoxicity.

SummaryObjectiveThymic neuroendocrine tumour (TH‐NET) accounts for almost 20% of multiple endocrine neoplasia type 1 (MEN1)‐associated mortality. Identifying risk factors for the development of these rare tumours and prognostic factors for clinical outcomes will be helpful in clinical practice.Design and PatientsWe performed a retrospective analysis of patients treated for TH‐NET associated with MEN1 in a single institution and meta‐analysis of literature reports. We used a fixed effect model to pool results across studies to evaluate the prevalence, clinical features and prognosis.ResultsTH‐NET was detected in 9 (7.4%) of 121 patients with MEN1 seen in our institution, and 5 (55.6%) were women. Seven additional studies were identified through a systematic review of the literature. The pool estimate of TH‐NET prevalence was 3.7% (n = 99) in MEN1 (n = 2710), sex ratio was 79:20 (male vs female), and the median age at diagnosis was 43.0 years (range, 16.0‐72.0 years). Forty‐three patients died with a median survival time of 8.4 years. Older age at diagnosis (HR = 1.4, 95% CI = 1.0‐1.8, P = .03), maximum tumour diameter (HR = 1.5, 95% CI = 1.0‐2.3, P = .04) and presence of metastasis (HR = 1.6, 95% CI = 1.0‐2.5, P = .04) were associated with worse outcome. A male predominance (91.9% vs 59.5%, P < .001) and history of smoking (59.0% vs 23.5%, P = .015) were more common in American/European series compared to Asian reports.ConclusionTH‐NET is a rare but fatal component of MEN1. Earlier detection of TH‐NET in patients with MEN1 may be recommended which should theoretically result in better outcomes. Different genetic backgrounds (race) appear to result in clinical difference.

Titin-truncating variants (TTNtvs) are the major cause of dilated cardiomyopathy (DCM); however, allelic heterogeneity (TTNtvs in different exons) results in variable phenotypes, and remains a major hurdle for disease diagnosis and therapy. Here, we generated a panel of ttn mutants in zebrafish. Four single deletion mutants in ttn.2 or ttn.1 resulted in four phenotypes and three double ttn.2/ttn.1 mutants exhibited more severe phenotypes in somites. Protein analysis identified ttnxu071 as a near-null mutant and the other six mutants as hypomorphic alleles. Studies of ttnxu071 uncovered a function of titin in guiding the assembly of nascent myofibrils from premyofibrils. By contrast, sarcomeres were assembled in the hypomorphic ttn mutants but either became susceptible to biomechanical stresses such as contraction or degenerated during development. Further genetic studies indicated that the exon usage hypothesis, but not the toxic peptide or the Cronos hypothesis, could account for these exon-dependent effects. In conclusion, we modeled TTNtv allelic heterogeneity during development and paved the way for future studies to decipher allelic heterogeneity in adult DCM.

ABSTRACT The Wnt/β-catenin pathway is implicated in left-right (LR) axis determination; however, the underlying mechanism remains elusive. Prompted by our recent discovery that Wnt signaling regulates ciliogenesis in the zebrafish Kupffer's vesicle (KV) via Foxj1a, a ciliogenic transcription factor, we decided to elucidate functions of Foxj1a in Wnt-regulated LR pattern formation. We showed that targeted injection of wnt8a mRNA into a single cell at the 128-cell stage is sufficient to induce ectopic foxj1a expression and ectopic cilia. By interrogating the transcription circuit of foxj1a regulation, we found that both Lef1 and Tcf7 bind to a consensus element in the foxj1a promoter region. Depletion of Lef1 and Tcf7 inhibits foxj1a transcription in the dorsal forerunner cells, downregulates cilia length and number in KV, and randomizes LR asymmetry. Targeted overexpression of a constitutively active form of Lef1 also induced an ectopic protrusion that contains ectopic transcripts for sox17, foxj1a, and charon, and ectopic monocilia. Further genetic studies using this ectopic expression platform revealed two distinct functions of Foxj1a; mediating Wnt-governed monocilia length elongation as well as charon transcription. The novel Foxj1a-charon regulation is conserved in KV, and importantly, it is independent of the canonical role of Foxj1a in the biosynthesis of motile cilia. Together with the known function of motile cilia movement in generating asymmetric expression of charon, our data put forward a hypothesis that Foxj1a confers both ciliary and non-ciliary functions of Wnt signaling, which converge on charon to regulate LR pattern formation.