Inter-plane feedback coordinates cell morphogenesis and maintains 3D tissue organization in the Drosophila pupal retina.

How complex organs coordinate cellular morphogenetic events to achieve three-dimensional (3D) form is a central question in development. The question is uniquely tractable in the late Drosophila pupal retina, where cells maintain stereotyped contacts as they elaborate the specialized cytoskeletal structures that pattern the apical, basal and longitudinal planes of the epithelium. In this study, we combined cell type-specific genetic manipulation of the cytoskeletal regulator Abelson (Abl) with 3D imaging to explore how the distinct cellular morphogenetic programs of photoreceptors and interommatidial pigment cells (IOPCs) organize tissue pattern to support retinal integrity. Our experiments show that photoreceptor and IOPC terminal differentiation is unexpectedly interdependent, connected by an intercellular feedback mechanism that coordinates and promotes morphogenetic change across orthogonal tissue planes to ensure correct 3D retinal pattern. We propose that genetic regulation of specialized cellular differentiation programs combined with inter-plane mechanical feedback confers spatial coordination to achieve robust 3D tissue morphogenesis.

Orthogonal coupling of a 3D cytoskeletal scaffold coordinates cell morphogenesis and maintains tissue organization in the Drosophila pupal retina.

How complex three-dimensional (3D) organs coordinate cellular morphogenetic events to achieve the correct final form is a central question in development. The question is uniquely tractable in the late Drosophila pupal retina where cells maintain stereotyped contacts as they elaborate the specialized cytoskeletal structures that pattern the apical, basal and longitudinal planes of the epithelium. In this study, we combined cell type-specific genetic manipulation of the cytoskeletal regulator Abelson (Abl) with 3D imaging to explore how the distinct cellular morphogenetic programs of photoreceptors and interommatidial pigment cells coordinately organize tissue pattern to support retinal integrity. Our experiments revealed an unanticipated intercellular feedback mechanism whereby correct cellular differentiation of either cell type can non-autonomously induce cytoskeletal remodeling in the other Abl mutant cell type, restoring retinal pattern and integrity. We propose that genetic regulation of specialized cellular differentiation programs combined with inter-plane mechanical feedback confers spatial coordination to achieve robust 3D tissue morphogenesis.

Ratiometric sensing of Pnt and Yan transcription factor levels confers ultrasensitivity to photoreceptor fate transitions in Drosophila.

Cell state transitions are often triggered by large changes in the concentrations of transcription factors and therefore large differences in their stoichiometric ratios. Whether cells can elicit transitions using modest changes in the ratios of co-expressed factors is unclear. Here, we investigate how cells in the Drosophila eye resolve state transitions by quantifying the expression dynamics of the ETS transcription factors Pnt and Yan. Eye progenitor cells maintain a relatively constant ratio of Pnt/Yan protein, despite expressing both proteins with pulsatile dynamics. A rapid and sustained twofold increase in the Pnt/Yan ratio accompanies transitions to photoreceptor fates. Genetic perturbations that modestly disrupt the Pnt/Yan ratio produce fate transition defects consistent with the hypothesis that transitions are normally driven by a twofold shift in the ratio. A biophysical model based on cooperative Yan-DNA binding coupled with non-cooperative Pnt-DNA binding illustrates how twofold ratio changes could generate ultrasensitive changes in target gene transcription to drive fate transitions. Thus, coupling cell state transitions to the Pnt/Yan ratio sensitizes the system to modest fold-changes, conferring robustness and ultrasensitivity to the developmental program.

Collaborative repressive action of the antagonistic ETS transcription factors Pointed and Yan fine-tunes gene expression to confer robustness in Drosophila.

The acquisition of cellular identity during development depends on precise spatiotemporal regulation of gene expression, with combinatorial interactions between transcription factors, accessory proteins and the basal transcription machinery together translating complex signaling inputs into appropriate gene expression outputs. The opposing repressive and activating inputs of the Drosophila ETS family transcription factors Yan and Pointed orchestrate numerous cell fate transitions downstream of receptor tyrosine kinase signaling, providing one of the premier systems for studying this process. Current models describe the differentiative transition as a switch from Yan-mediated repression to Pointed-mediated activation of common target genes. We describe here a new layer of regulation whereby Yan and Pointed co-occupy regulatory elements to repress gene expression in a coordinated manner, with Pointed being unexpectedly required for the genome-wide occupancy of both Yan and the co-repressor Groucho. Using even skipped as a test-case, synergistic genetic interactions between Pointed, Groucho, Yan and components of the RNA polymerase II pausing machinery suggest that Pointed integrates multiple scales of repressive regulation to confer robustness. We speculate that this mechanism may be used broadly to fine-tune the expression of many genes crucial for development.

Detecting differential copy number variation between groups of samples.

We present a method to detect copy number variants (CNVs) that are differentially present between two groups of sequenced samples. We use a finite-state transducer where the emitted read depth is conditioned on the mappability and GC-content of all reads that occur at a given base position. In this model, the read depth within a region is a mixture of binomials, which in simulations matches the read depth more closely than the often-used negative binomial distribution. The method analyzes all samples simultaneously, preserving uncertainty as to the breakpoints and magnitude of CNVs present in an individual when it identifies CNVs differentially present between the two groups. We apply this method to identify CNVs that are recurrently associated with postglacial adaptation of marine threespine stickleback (Gasterosteus aculeatus) to freshwater. We identify 6664 regions of the stickleback genome, totaling 1.7 Mbp, which show consistent copy number differences between marine and freshwater populations. These deletions and duplications affect both protein-coding genes and cis-regulatory elements, including a noncoding intronic telencephalon enhancer of DCHS1 The functions of the genes near or included within the 6664 CNVs are enriched for immunity and muscle development, as well as head and limb morphology. Although freshwater stickleback have repeatedly evolved from marine populations, we show that freshwater stickleback also act as reservoirs for ancient ancestral sequences that are highly conserved among distantly related teleosts, but largely missing from marine stickleback due to recent selective sweeps in marine populations.

Evaluation of absolute serum α-fetoprotein levels in liver transplant for hepatocellular cancer.

HYPOTHESIS: An elevated serum α-fetoprotein (AFP) level before orthotopic liver transplant (OLT) is predictive of mortality after OLT for hepatocellular carcinoma (HCC). DESIGN: Retrospective analysis of a population-based cohort. SETTING: United Network for Organ Sharing registry (2003-2008). PATIENTS: We identified 2253 patients who underwent OLT for HCC with available pre-OLT serum AFP values. METHODS: Patients were stratified by AFP levels into low (<20 ng/mL), medium (20-399 ng/mL), or high (≥400 ng/mL) groups. Clinical and pathological characteristics were compared among groups. Survival curves were constructed by the Kaplan-Meier method, and univariate and multivariate Cox-regression analysis was performed. RESULTS: Of the 2253 patients, 1210 (53.7%), 805 (35.7%), and 238 (10.6%) were in the low, medium, and high AFP groups, respectively. On univariate analysis, the low AFP group demonstrated the best 4-year survival (76%) compared with the medium (65%; P = .001) and high (57%; P < .001) AFP groups. When AFP levels in patients with only stage II HCC underwent assessment, improved survival in the low AFP group was still observed (P < .001). On multivariate analysis, the medium and high AFP groups were associated with higher mortality (hazard ratios, 1.50 [95% confidence interval, 1.19-1.89; P = .001] and 2.11 [1.55-2.88; P < .001], respectively). CONCLUSIONS: Serum AFP level is an independent prognostic predictor of outcome after OLT for HCC. The association between serum AFP value and post-OLT survival warrants further investigation to potentially better allocate donor allografts for HCC.

Race, ethnicity, and socioeconomic status influence the survival of patients with hepatocellular carcinoma in the United States.

BACKGROUND: Racial, ethnic, and socioeconomic disparities in the survival of patients with hepatocellular carcinoma (HCC) continue to exist. The authors of this report hypothesized that these differences result from inequities in access to care and in response to therapy. METHODS: Patients with HCC (n = 20,920) were identified from the Surveillance, Epidemiology, and End Results (SEER) database, and patients who underwent liver transplantation for HCC (n = 4735) were identified from the United Network for Organ Sharing (UNOS) database. Clinical and pathologic factors were compared after patients were stratified by race and ethnicity. RESULTS: The survival of patients with HCC improved over time for all racial, ethnic, and income groups (P < .001). Black and low income individuals had the poorest long-term survival (P < .001). On multivariate analysis, black race was predictive of the poorest survival (hazard ratio [HR], 1.15; 95% confidence interval [CI], 1.09-1.22; P < .001), whereas Asian race was associated with the best survival (HR, 0.87; 95% CI, 0.83-0.91; P < .001). After liver transplantation, black patients had the worst graft survival and overall survival (median survival [MS], 30.5 months and 39.7 months, respectively; P < .001), whereas Hispanics had the best survival (MS, 83.4 months and 86.6 months, respectively; P < .001). In a multivariate analysis of transplantation patients, race and ethnicity were associated significantly with outcome. CONCLUSIONS: Significant racial and ethnic disparities in the outcome of patients with HCC persist despite the receipt of comparable treatment. The authors concluded that further investigations are warranted to identify the reasons for the stark disparity in outcomes between black patients and Hispanic patients after liver transplantation for HCC.

A disease-based comparison of liver transplantation outcomes.

An increasing demand for transplant donor organs has made optimal allocation of resources a priority. Our objective was to evaluate outcomes for orthotopic liver transplantation (OLT) performed in the United States. A query of the United Network for Organ Sharing registry between 1988 and 2007 was performed for patients who underwent OLT for all etiologies. Patients were stratified by pathology necessitating OLT and clinical and pathologic factors were compared. Multivariate Cox-regression analysis was used to assess the association of pathology with survival. Of 61,823 patients, 33 per cent (n = 20,305) of OLTs were secondary to hepatitis C virus, 21 per cent autoimmune disease, 17 per cent alcohol-induced injury, 11 per cent cryptogenic cirrhosis, 8 per cent hepatocellular carcinoma (HCC), 6 per cent hepatitis B virus, and 4 per cent metabolic disease. Patients with autoimmune disease and HCC demonstrated the best and worst survival, respectively, after OLT (median survival 16.0 vs 6.4 yrs, respectively, P < 0.001). By multivariate analysis, OLT for HCC was significantly associated with poorer overall survival (hazard ratio [HR] 2.19, 95% confidence interval [CI]: 2.02-2.37, P < 0.001). Our results indicate that outcomes for liver transplantation vary by primary hepatic pathology with HCC patients having the poorest overall survival. To optimize organ allocation for all patients with end-stage liver disease, a better understanding of poor survival for HCC is necessary.

Surgical resection of primary and metastatic hepatic malignancies following portal vein embolization.

BACKGROUND: Portal vein embolization (PVE) has been used to induce hypertrophy in future liver remnants (FLRs) in preparation for major hepatic resection. We report our initial experience with PVE and identify potential predictors of unresectability following PVE. METHODS: Patients with primary and metastatic hepatic malignancies (n = 20) who underwent PVE between 2004 and 2008 were categorized by surgical resection status and clinicopathologic factors were compared. RESULTS: The cohort had the following histologies: colorectal adenocarcinoma (45%, n = 9), hepatocellular carcinoma (20%), cholangiocarcinoma (20%), and other (15%). Seven patients (35%) had previous liver-directed or regional therapy; 55% subsequently underwent successful liver resection, whereas 45% were deemed unresectable. Patients who underwent successful resection had tumor shrinkage after PVE compared to unresectable patients (% change in maximal tumor diameter, -6% vs. +45%, respectively; P = 0.027) and had a lower rate of baseline liver function test abnormality (0% vs. 56%, respectively; P = 0.004). Resected patients had an 83% 5-year overall survival. CONCLUSIONS: Baseline liver dysfunction may predict subsequent unresectable hepatic disease following PVE and tumor progression after PVE appears to increase the likelihood for finding unresectable hepatic disease. Select patients should be considered for PVE with careful surveillance during the period of FLR hypertrophy.