Biomedical subjects

Byung Joon Hwang

Publications and source records attributed to Byung Joon Hwang.

6 recordsLinked to original sources

PubMed2007

C. elegans EVI1 proto-oncogene, EGL-43, is necessary for Notch-mediated cell fate specification and regulates cell invasion.

During C. elegans development, LIN-12 (Notch) signaling specifies the anchor cell (AC) and ventral uterine precursor cell (VU) fates from two equivalent pre-AC/pre-VU cells in the hermaphrodite gonad. Once specified, the AC induces patterned proliferation of vulva via expression of LIN-3 (EGF) and then invades into the vulval epithelium. Although these cellular processes are essential for the proper organogenesis of vulva and appear to be temporally regulated, the mechanisms that coordinate the processes are not well understood. We computationally identified egl-43 as a gene likely to be expressed in the pre-AC/pre-VU cells and the AC, based on the presence of an enhancer element similar to the one that transcribes lin-3 in the same cells. Genetic epistasis analyses reveal that egl-43 acts downstream of or parallel to lin-12 in AC/VU cell fate specification at an early developmental stage, and functions downstream of fos-1 as well as upstream of zmp-1 and him-4 to regulate AC invasion at a later developmental stage. Characterization of the egl-43 regulatory region suggests that EGL-43 is a direct target of LIN-12 and HLH-2 (E12/47), which is required for the specification of the VU fate during AC/VU specification. EGL-43 also regulates basement membrane breakdown during AC invasion through a FOS-1-responsive regulatory element that drives EGL-43 expression in the AC and VU cells at the later stage. Thus, egl-43 integrates temporally distinct upstream regulatory events and helps program cell fate specification and cell invasion.

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PubMed2006

SynMuv genes redundantly inhibit lin-3/EGF expression to prevent inappropriate vulval induction in C. elegans.

Activation of EGFR-Ras-MAPK signaling in vulval precursor cells (VPCs) by LIN-3/EGF from the gonad induces vulval development in C. elegans. The prevailing view is that LIN-3 overcomes an "inhibitory signal" from the adjacent hyp7 hypodermal syncytium. This view originated from observations indicating that inactivation of functionally redundant Synthetic Multivulva (SynMuv) genes in hyp7 can activate EGFR-Ras-MAPK signaling in the VPCs. Many SynMuv genes encode transcription and chromatin-associated factors, including the Rb ortholog. Here, we show that the SynMuv A and SynMuv B gene classes are functionally redundant for transcriptional repression of the key target gene, lin-3/EGF, in the hypodermis. These observations necessitate a revision of the concept of "inhibitory signaling." They also underscore the importance of preventing inappropriate cell signaling during development and suggest that derepression of growth factors may be the mechanism by which tumor suppressor genes such as Rb can have cell nonautonomous effects.

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PubMed2006

Electrophoretic mobility shift assays to study protein binding to damaged DNA.

The electrophoretic mobility shift assay (EMSA) can be used to identify proteins that bind specifically to damaged DNA. EMSAs detect the presence of key DNA repair proteins, such as ultraviolet (UV)-damaged DNA binding protein, which is involved in nucleotide excision repair, and Ku and DNA-PKcs, which are involved in double-strand break repair. This chapter describes EMSA protocols for detecting proteins that bind to UV-damaged DNA, cisplatin-damaged DNA, and DNA ends. The chapter also describes variations of the EMSA that can be used to obtain additional information about these important proteins. The variations include the reverse EMSA, which can detect binding of 35S-labeled protein to damaged DNA, and the antibody supershift assay, which can define the composition of protein-DNA complexes.

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PubMed2004

Genome annotation by high-throughput 5' RNA end determination.

Complete gene identification and annotation, including alternative transcripts, remains a challenge in understanding genome organization. Such annotation can be achieved by a combination of computational analysis and experimental confirmation. Here, we describe a high-throughput technique, trans-spliced exon coupled RNA end determination (TEC-RED), that identifies 5' ends of expressed genes in nematodes. TEC-RED can distinguish coding regions from regulatory regions and identify genes as well as their alternative transcripts that have different 5' ends. Application of TEC-RED to approximately 10% of the Caenorhabditis elegans genome yielded tags 75% of which experimentally verified predicted 5'-RNA ends and 25% of which provided previously unknown information about 5'-RNA ends, including the identification of 99 previously unknown genes and 32 previously unknown operons. This technique will be applicable in any organisms that have a trans-splicing reaction from spliced leader RNA. We also describe an efficient sequential method for concatenating short sequence tags for any serial analysis of gene expression-like techniques.

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PubMed2003

A cell-specific enhancer that specifies lin-3 expression in the C. elegans anchor cell for vulval development.

During C. elegans vulval development, the anchor cell (AC) in the somatic gonad expresses lin-3, activating the EGF receptor signaling pathway in vulval precursor cells (VPCs) and thereby inducing and patterning VPCs. Previous studies with lin-3 mutants and transgene expression have revealed that the level of LIN-3 in the AC must be precisely regulated for proper vulval development. To understand how lin-3 expression is achieved in the AC, we identified a 59 bp lin-3 enhancer sufficient to activate lin-3 transcription solely in the AC. The enhancer contains two E-box elements, and one FTZ-F1 nuclear hormone receptor (NHR) binding site that is mutated in a vulvaless mutant, lin-3(e1417). Mutagenesis studies show that both E-boxes and the NHR binding site are necessary to express lin-3 in the AC. In vitro DNA-binding studies and in vivo functional assays indicate that distinct trans-acting factors, including the E-protein/Daughterless homolog HLH-2 and unidentified nuclear hormone receptor(s), are necessary for lin-3 transcription in the AC and thus are involved in vulval development.

Animals↗

PubMed2002

Interaction between UV-damaged DNA binding activity proteins and the c-Abl tyrosine kinase.

The c-Abl tyrosine kinase is activated by some forms of DNA damage, including ionizing radiation, but not UV radiation. The functions of this activation in the damage response pathways remain obscure. To identify potential targets of c-Abl kinase, we utilized the yeast two-hybrid system to screen a murine cDNA library. One c-Abl binding protein of particular interest was the large subunit (DDB1) of the heterodimeric complex with UV-damaged DNA binding activity (UV-DDB). This complex binds with high specificity to DNA damaged by UV, is absent in a subset of xeroderma pigmentosum group E cells, and is required for global genomic repair of UV-induced damage. The association of c-Abl with DDB1 required the kinase domain of c-Abl and preserved the interaction between DDB1 and the small subunit (DDB2) of the UV-DDB complex. Significantly, overexpression of c-Abl increased tyrosine phosphorylation of DDB2 and suppressed UV-DDB activity. Conversely, a dominant negative, kinase-deficient allele of c-Abl decreased tyrosine phosphorylation of DDB2 and dramatically stimulated UV-DDB activity. These results suggest that one role of c-Abl may be to negatively regulate UV-DDB activity by phosphorylation of DDB2.

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