Biology subjects

Gao, C.

Publications and source records attributed to Gao, C..

167 records · Page 10Linked to original sources

bioRxiv2018

Zebrafish hhex null mutant develops an intrahepatic intestinal tube due to de-repression of cdx1b and pdx1

The hepatopancreatic duct (HPD) system links the liver and pancreas to the intestinal tube and is composed of the extrahepatic biliary duct, gallbladder and pancreatic duct. Haematopoietically-expressed-homeobox (Hhex) protein plays an essential role in the establishment of HPD, however, the molecular mechanism remains elusive. Here we show that zebrafish hhex-null mutants fail to develop the HPD system characterized by lacking the biliary marker Annexin A4 and the HPD marker sox9b. The mutant HPD system is replaced by an intrahepatic intestinal tube characterized by expressing the intestinal marker fatty-acid-binding-protein 2a (fabp2a). Cell lineage analysis showed that this intrahepatic intestinal tube is not originated from hepatocytes or cholangiocytes. Further analysis revealed that cdx1b and pdx1 were expressed ectopically in the intrahepatic intestinal tube and knockdown of cdx1b and pdx1 restored the expression of sox9b in the mutant. Chromatin-immunoprecipitation analysis shows that Hhex binds to the promoters of pdx1 and cdx1b genes to repress their expression. We therefore propose that Hhex, Cdx1b and Pdx1 form a genetic network governing the patterning and morphogenesis of the HPD and digestive tract systems in zebrafish.

developmental biology↗

bioRxiv2017

Hi-TOM: a platform for high-throughput tracking of mutations induced by CRISPR/Cas systems

The CRISPR/Cas system has been extensively applied to make precise genetic modifications in various organisms. Despite its importance and widespread use, large-scale mutation screening remains time-consuming, labour-intensive and costly. Here, we describe a cheap, practicable and high-throughput screening strategy that allows parallel screening of 96 x N (N denotes the number of targets) genome-modified sites. The strategy simplified and streamlined the process of next-generation sequencing (NGS) library construction by fixing the bridge sequences and barcoding primers. We also developed Hi-TOM (available at http://www.hi-tom.net/hi-tom/), an online tool to track the mutations with precise percentage. Analysis of the samples from rice, hexaploid wheat and human cells reveals that the Hi-TOM tool has high reliability and sensitivity in tracking various mutations, especially complex chimeric mutations that frequently induced by genome editing. Hi-TOM does not require specially design of barcode primers, cumbersome parameter configuration or additional data analysis. Thus, the streamlined NGS library construction and comprehensive result output make Hi-TOM particularly suitable for high-throughput identification of all types of mutations induced by CRISPR/Cas systems.

bioinformatics↗

bioRxiv2017

Highly tamoxifen-inducible principal-cell-specific Cre mice with complete fidelity in cell specificity and no leakiness

An ideal inducible system should be cell-specific and have absolute no background recombination without induction (i.e. no leakiness), a high recombination rate after induction, and complete fidelity in cell specificity (i.e. restricted recombination exclusively in cells where the driver gene is expressed). However, such an ideal mouse model remains unavailable for collecting duct research. Here, we report a mouse model that meets these criteria. In this model, a cassette expressing ERT2CreERT2 (ECE) is inserted at the ATG of the endogenous Aqp2 locus to disrupt Aqp2 function and to express ECE under the control of the Aqp2 promoter. The resulting allele is named Aqp2ECE. There was no indication of a significant impact of disruption of a copy of Aqp2 on renal function and blood pressure control in adult Aqp2ECE/+ heterozygotes. Without tamoxifen, Aqp2ECE did not activate a Cre-dependent red fluorescence protein (RFP) reporter in adult kidneys. A single injection of tamoxifen (2 mg) to adult mice enables Aqp2ECE to induce robust RFP expression in the whole kidney 24h post injection, with the highest recombination efficiency of 95% in the inner medulla. All RFP-labeled cells expressed principal cell markers (Aqp2 & Aqp3), but not intercalated cell markers (V-ATPase B1B2, and carbonic anhydrase II). Hence, Aqp2ECE confers principal cell-specific tamoxifen-inducible recombination with absolute no leakiness, high inducibility, and complete fidelity in cell specificity, which should be an important tool for temporospatial control of target genes in the principal cells and for Aqp2+ lineage tracing in adult mice.

genetics↗

bioRxiv2017

A library of structurally homogeneous human N-glycans synthesized from microbial oligosaccharide precursors

Synthesis of homogenous glycans in quantitative yields represents a major bottleneck to the production of molecular tools for glycoscience, such as glycan microarrays, affinity resins, and reference standards. Here, we describe a combined biological/enzymatic method termed bioenzymatic synthesis that is capable of efficiently converting microbially-derived precursor oligosaccharides into structurally uniform human-type N-glycans. Unlike starting material obtained by chemical synthesis or direct isolation from natural sources, which can be time consuming and costly to generate, bioenzymatic synthesis involves precursors derived from renewable sources including wild-type Saccharomyces cerevisiae glycoproteins and lipid-linked oligosaccharides from glycoengineered Escherichia coli. Following deglycosylation of these biosynthetic precursors, the resulting microbial oligosaccharides are subjected to a greatly simplified purification scheme followed by structural remodeling using commercially available and recombinantly produced glycosyltransferases including key N- acetylglucosaminyltransferases (e.g., GnTI, GnTII, and GnTIV) involved in early remodeling of glycans in the mammalian glycosylation pathway. Using this approach, preparative quantities of hybrid and complex-type N-glycans including asymmetric multi-antennary structures were generated all without the need of a specialized skillset. Collectively, our results reveal bioenzymatic synthesis to be a user-friendly methodology for rapidly supplying homogeneous oligosaccharide structures that can be used to understand the human glycome and probe the biological roles of glycans in health and disease.

biochemistry↗

bioRxiv2016

Tractography-based connectomes are dominated by false-positive connections

Fiber tractography based on non-invasive diffusion imaging is at the heart of connectivity studies of the human brain. To date, the approach has not been systematically validated in ground truth studies. Based on a simulated human brain dataset with ground truth white matter tracts, we organized an open international tractography challenge, which resulted in 96 distinct submissions from 20 research groups. While most state-of-the-art algorithms reconstructed 90% of ground truth bundles to at least some extent, on average they produced four times more invalid than valid bundles. About half of the invalid bundles occurred systematically in the majority of submissions. Our results demonstrate fundamental ambiguities inherent to tract reconstruction methods based on diffusion orientation information, with critical consequences for the approach of diffusion tractography in particular and human connectivity studies in general.

neuroscience↗