Molecular Mechanisms of Gene-Dosage Effect in Down syndrome

Down syndrome (DS), the phenotypic manifestation of trisomy 21, is one of the most common genetic abnormalities. The syndrome results from the presence of extra chromosome 21 in each and every cell of the affected fetuses. DS patient suffer from a wide range of defects some of which afflict the general population. However, in DS individuals these defects always occur at a much higher frequency and earlier in life. Since the discovery in 1959 that DS phenotype is caused by trisomy of chromosome 21, the prevailing dogma was that DS pathology results from gene-dosage imbalance, in the sense that overproduction of some (or all) of the proteins encoded by chromosome 21 genes disturbs the metabolic balance required for proper development and normal function.  However, there was no molecular, Koch Postulates type evidence supporting this assumption. To investigate this issue, we have cloned SOD1, the first chromosome 21 gene to be cloned, and demonstrated that extra copies of the gene produce in transgenic mice abnormalities similar to the anatomical and clinical symptoms observed in patients with DS. In so doing we have proved the gene-dosage effect theory in trisomy 21 and opened the door into a new era in DS research. .

Research in the lab address disease conditions in which genetic predisposition of individual chromosome 21 genes play role. The broad long-term objective of our research is to elucidate, at the molecular level, how an extra copy of otherwise normal genes produces pathophysiological conditions in humans particularly in patients with DS. Transgenic and gene-Knockout mice of individual genes are used to investigate the consequences of functional gene-dosage of the candidate genes.

Currently much of our studies focused on the biology of two transcription factors Runx1 and Runx3 that belong to the RUNX gene family. The RUNX genes arose early in evolution and maintained extensive structural similarities in mammals (Fig 1). RUNX1 reside on chromosome 21 and its potential involvement in DS leukemia is addressed. RUNX3 reside on chromosome 1 at 1p36.1 in a region known to be involved in several important human diseases (Fig 1).

The RUNX are master regulators of linage specific gene expression in several important developmental pathways. One of the exciting questions in molecular biology is how differential gene expression patterns are established and maintained during development. While the lab is molecular biology oriented our notion has been that it is not sufficient to study the biochemical mechanisms in cell culture and that in depth understanding entails experiments in animal models.

To this end we investigate the biology of Runx1 and Runx3 both in vitro at the molecular level and in vivo using genetically modified mouse models (Fig 2).

Figure 1 RUNX genes phylogeny, gene structure and elements involved in expression regulation. A. Phylogenetic illustration of RUNX genes showing the gene number and promoter usage in different animals. The more primitive animals contain one gene regulated by the P2 promoter. B. Genomic organization of the human RUNX genes. Chromosomal localizations and conserved neighboring genes (CLIC and DSCR) are depicted.

Figure 2

Recently published relevant article.

Levanon, D., Bettoun, D., Harris-Cerruti, C., Woolf, E., Negreanu, V., Eilam, R., Bernstein, Y., Goldenberg, D., Xiao, C., Fliegauf, M., Kremer, E., Otto, F., Brenner, O., Lev-Tov, A. and Groner, Y. The Runx3 transcription factor regulates development and survival of TrkC dorsal root ganglia neurons.  EMBO J. 21: 3454-3463 (2002). PDF Version

Bartfeld, D., Shimon, L., Couture, G.C., Rabinovich, D., Frolow, F., Levanon, D., Groner, Y. and Shaked Z.  DNA recognition by the RUNX1 transcription factor is mediated by an allosteric transition in the RUNT domain and by DNA bending.  Structure (Camb)  10: 1395-1407, (2002). PDF Version

Woolf, E., Xiao, C., Fainaru, O., Lotem, J., Rosen, D., Negreanu, V., Bernstein, Y., Goldenberg, D, Brenner, O., Berke, G., Levanon, D. and Groner, Y. Runx3 and Runx1 are required for CD8 T cell development during thymopoiesis. Proc Natl Acad Sci USA. 100: 7731-7736.  (2003). PDF Version

Levanon, D., Brenner, O., Otto, F. and Groner, Y. Runx3 knockouts and stomach cancer.  EMBO Rep. Jun;4(6):560-564 (2003). PDF Version

Fainaru, O., Woolf, E., Lotem, J., Yarmus, M., Brenner, O., Goldenberg, D., Negreanu, V., Bernstein, Y., Levanon, D., Jung, S. and Groner, Y.  Runx3 regulates mouse TGF-beta-mediated dendritic cell function and its absence results in airway inflammation.  EMBO J. 23:969-979 (2004).

Harris-Cerruti, C., Kamsler, A., Kaplan, B., Lamb, B., Segal, M. and Groner, Y. Functional and morphological alterations in compound transgenic mice overexpressing Cu/Zn superoxide dismutase and amyloid precursor protein (correction). Eur J Neurosci. 19: 1174-90. Erratum in: Eur J Neurosci. 2004 19: 2913 (2004).

Levanon, D. and Groner, Y. Structure and regulated expression of mammalian RUNX genes.  Oncogene. 23:  4211-4219 (2004).

Brenner, O., Levanon, D., Negreanu, V., Golubkov, O., Fainaru, O., Woolf, E. and Groner, Y. Loss of Runx3 function in leukocytes is associated with spontaneously developed colitis and gastric mucosal hyperplasia. Proc Natl Acad Sci USA. 101: 16016-16021 (2004).

Raveh, E., Cohen, S., Levanon, D., Groner, Y. and Gat, U. Runx3 is involved in hair shape determination.  Dev Dyn. 233: 1478-1487 (2005).

Fainaru, O., Shseyov, D., Hantisteanu, S. and Groner, Y. Accelerated chemokine receptor 7-mediated dendritic cell migration in Runx3 knockout mice and the spontaneous development of asthma-like disease. Proc Natl Acad Sci USA. 102: 10598-10603 (2005).

Marmigere, F., Montelius, A., Wegner, M., Groner, Y., Reichardt, L.F. and Ernfors, P. The Runx1/AML1 transcription factor selectively regulates development and survival of TrkA nociceptive sensory neurons.  Nat Neurosci. 9: 180-187 (2006).

Yarmus, M., Woolf, E., Bernstein, Y., Fainaru, O., Negreanu, V., Levanon, D. and Groner, Y. Groucho/transducin-like Enhancer-of-split (TLE)-dependent and -independent transcriptional regulation by Runx3. Proc Natl Acad Sci USA. 103: 7384-7389 (2006).

Raveh, E., Cohen, S., Levanon, D., Negreanu, V., Groner, Y. and Gat, U. Dynamic expression of Runx1 in skin affects hair structure.  Mech Dev. 123: 842-850 (2006).

Hinoi, E., Bialek, P., Chen, Y.T., Rached, M.T., Groner, Y., Behringer, R.R., Ornitz, D.M. and Karsenty, G. Runx2 inhibits chondrocyte proliferation and hypertrophy through its expression in the perichondrium.  Genes Dev. 20: 2937-2942 (2006).

Djuretic, I.M., Levanon, D., Negreanu, V., Groner, Y., Rao, A. and Ansel, K.M. Transcription factors T-bet and Runx3 cooperate to activate Ifng and silence Il4 in T helper type 1 cells. Nat Immunol. 8: 145-153 (2007).

Woolf, E., Brenner, O., Goldenberg, D., Levanon, D. and Groner, Y. Runx3 regulates dendritic epidermal T cell development. Dev Biol. 303: 703-714 (2007).

Fainaru, O., Shay, T., Hantisteanu, S., Goldenberg, D., Domany, E. and Groner, Y. TGFbeta-dependent gene expression profile during maturation of dendritic cells. Genes Immun. 8: 239-244 (2007).Pozner, A., Lottem, J., Xiao, C., Goldenberg, D., Brenner, O., Negreanu, V., Levanon, D., and Groner, Y. Developmentally regulated promoter-switch transcriptionally controls Runx1 funaction during embryonic hematopoiesis. BMC Dev Biol. 7:84, 1-19 (2007).