候玉恭文章公布转录研究新发现

　　

生物通报道：真核细胞基因的活化通常都依赖于遥远的染色质决定因子。但是，到目前为止，人们还对这些决定元件如何起功能还知之甚少。在最新一期的Molecular Cell杂志上，来自宾西法尼亚州大学医学院的华人科研人员候玉恭（Yugong Ho）等人公布了有关长距离基因活化中位置控制区域转录功能的新发现。

人类生长激素基因（hGH基因）能被一个5’远端LCR（locus control region）活化。LCR是一段控制染色质紧密程度的调控序列，能调控相距较远的基因或基因簇是否可以被接近并表达。垂体特异性DNA酶I超敏感位点I（HSI）——hGH的LCR元件的结构域与hGH-N启动子间隔14.5kb，包围着B淋巴特异性CD79b基因。

在这项新研究中，候博士（文章第一作者）等人描绘了包含hGH LCR和毗邻的CD79D基因座的垂体somatotropes中非编码Pol II转录的一个区域。

这种完整的LCR转录区域依赖于HIS，并终止于3’端的CD79b，从而使这个区域和靶标hGH-N启动子间形成一个间隙。

将一个Pol II终结因子插入导LCR中时，能抑制CD79b的转录并抑制hGH-N的表达。这些数据揭示出了LCR转录在长距离的基因活化控制中起到一个关键的作用，并且将看似无关的CD79b的转录也联系到这个过程中。（生物通记者杨遥）

候玉恭（Yugong Ho）博士简介：

Education
1999, Ph.D., Temple University

Current Research
A set of distal human growth hormone (hGH) cluster locus control regions (LCR), identified initially by their DNase I hypersensitivity (HS), have been shown to be essential for the tissue-restricted expression of hGH gene. A 1.6 kb fragment of the LCR containing only HS I,II is sufficient to confer a high-level of hGH-N expression in pituitaries of transgenic mice when the fragment is juxtaposed to the hGH gene.

One of my projects is to study the cis-acting HS I,II in the context of the intact hGH locus. A bacteriophage P1-clone containing the majority of the hGH cluster and the full set of the LCR is identified in this lab. I am using RecA-assisted homologous recombination to mutate the HS I, II region in the P1 clone. The expression of the hGH will be studied in transgenic mice carrying the mutated LCR and hGH cluster to characterize the role(s) of the HS I,II in tissue-specific expression of the hGH. The minimum sequence required for the HS I,II cis-acting activity will be identified using this approach. I am also going to determine whether HS I,II acts as the sole determinant of somatotrope specificity of hGH by deleting the HS I,II region using the same approach.

The second project I am interested is to study whether hGH LCR is conserved in the mouse growth hormone (mGH) gene. Our hypothesis is that sequence- and functional-homologues of the hGH LCR have been evolutionarily preserved in the mouse genome. P1 clones containing the mGH and 5'-flanking region of the mGH are identified. The sequence homologous to the hGH LCR in the mGH 5'-flanking region will be identified. DNase I mapping will be performed in the DNA of the mGH ant 5'-flanking region in intact chromatin isolated from pituitaries of mouse line expresses high-level GH to investigate whether the sequence homologous to hGH LCR is DNase I hypersensitive. Any additional HS site in mGH locus will also be identified using this approach. These HS sites will be deleted from the mouse genome and the expression of mGH will be studied to characterize the role(s) of these HS sites.

发表的部分文章：

1. Ho, Y., Doherty, A.S. and Schultz, R.M. (1994). Mouse preimplantation embryo development in vitro: effect of sodium concentration an culture media on RNA synthesis and accumulation and gene expression. Mol. Repro. and Dev., 38, 131-141

2.      Ho, Y., Wigglesworth, K., Eppig, J.J. and Schultz, R.M. (1995) Preimplantation development of mouse embryo in KSOM: augmentation by amino acid and analysis of gene expression. Mol. Repro. and Dev., 41,232-238.

3.      Ho, Y., Kim, S and Waring R.B. (1997) A protein encoded by a group I intron directly assists RNA splicing and is a DNA endonuclease. Proc. Natl. Acad. Sci.USA, 94, 8994-8999.

4.      Ho, Y., and Waring R.B. (1999). The maturase encoded by a group I intron from Aspergillus nidulans stabilizes RNA tertiary structure and promotes rapid splicing. J.Mol.Biol., 292,987-1001.

Ho, Y., Elefant, F., Cooke, N.E. and Liebhaber, S.A. (2001). A Defined Locus Control Region Determinant Mediates Chromatin Domain Acetylation and Remote Gene Activation. Submitted.