Biological Regulation


Nava Dekel, Head
The Philip M. Klutznick Professorial Chair of Developmental Biology

The regulation of processes responsible for the concerted action of cells, tissues, vascular networks and organs is being carried out in our department. Our studies include the identification of signaling pathways involving hormones, growth promoting factors, as well as programmed cell death and survival factors. We also characterize specific receptors, target cells, and the multiple mechanisms involved in the transmission of signals as well as processing and regulation of developmental and differentiation events. In these investigations we apply a diverse range of methodologies in different in vitro and in vivo systems: namely, biochemical, molecular biology, and physiological methods in tissue cultures, organs and whole animals. We also focus on developing non-invasive imaging technology by the utilization of optical means, as well as magnetic resonance imaging (MRI) and spectroscopy (MRS). Since changes in the regulation of such processes are a cause for many human diseases (cancer, infertility, heart failure, stroke etc.), we further apply our results to develop new modes of treatment, such as photodynamic cancer therapy, and drugs for pharmacological intervention.

Hadassa Degani: This year, our lab focused on investigating hormonal regulation of breast cancer, monitoring and searching the steps associated with breast cancer metastasis, as well as discovering molecular and biochemical processes associated with breast malignant transformation. The experiments were performed on human breast cancer cells growing in culture, as well as on orthotopic tumors of these cells implanted in experimental animals in vivo. In addition, we extended our studies to lung cancer cells and tumors growing in the lung, searching for the distinct properties of the microvascular network of this cancer. In the course of these investigations we developed novel, non invasive methods for monitoring cancer progression and metastasis by means of magnetic resonance and fluorescence imaging . For example, we developed a method which enabled us to map the distribution of the interstitial fluid pressure and thereby determine the barriers to drug delivery, and resistance to chemotherpy. Moreover, In collaboration with Prof. David Milstein, Organic Chemistry, we synthesized and demonstrated the application of novel molecular MRI probes for mapping in vivo the expression of the estrogen receptor in breast cancer tumors and rat uteri. In collaboration with Medical Centers in the US and Taiwan we continued our clinical MRI investigations of prostate cancer staging and breast cancer response to chemotherapy.

Nava Dekel: Studies in our laboratory are directed at identification and characterization of molecular events that regulate reproduction and early development. Of major interest is the control of the meiotic status of the mammalian oocyte. Attempts to disclose this issue include investigation of the gating mechanism of the gap junctions that mediate the communication of the inhibitory cAMP from the somatic cells of the ovarian follicle to the oocyte and the response of the ovarian gap junction protein connexin 43 (Cx43) to gonadotropins. Exploration of ovarian biochemical events that mediate gonadotropin action to stimulate the resumption of meiosis include the mode of activation of the EGF receptor as well as its downstream ERK1/2. Search for complementary mechanisms that ensure the efficiency of a timely alteration between meiotic arrest and resumption of meiosis include the characterization of the oocyte specific phosphodiesterase 3A (PDE3A) and its possible mode of regulation during meiotic arrest and upon reinitiation of meiosis. Potential downstream regulators that are subjected to the PKA-mediated cAMP action are examined and their hierarchy is explored. Specific interest is directed at the role of ECT2 and RhoA that participate in the completion of the first meiotic division.

A list of ovarian and endometrial genes, the expression of which is upregulated in association with ovulation and implantation, respectively have been recently generated by suppression subtructive hybridization (SSH) and microarray analysis. Further attempts to characterize and identify the specific function of a selected group of these genes are presently performed. Our studies on implantation and early embryonal development are also directed at exploration of the involvement of the immune system in the embryo-uterus dialog. These studies that are performed in collaboration with the IVF unit at the Kaplan Medical Center already resulted in the development of a new protocol for treatment of infertility that is associated with failure of implantation.

Dr. Lilach Gilboa "Gonad morphogenesis and establishment of germ line stem cells in Drosophila melanogaster": Many organs rely on stem cells for normal development, function and regeneration. The adult ovary of Drosophila employs germ line stem cells (GSCs) for the continual production of eggs throughout the lifetime of the animal. The known location of GSCs and the genetic tools available for Drosophila research have made the adult ovary a leading system in understanding the principles of stem cell biology. Despite the wealth of information regarding adult GSCs, less is known about how, during larval development, the adult niche forms and how it affects GSC establishment of from primordial germ cells (PGCs). Our lab studies two aspects of larval ovary development: A. How the somatic cells of the ovary control proliferation of PGCs, thereby determining the number of stem cells the adult ovary will contain, and B. How the somatic niches for GSCs form, and how niche formation contributes to the establishment of GSCs from PGCs. PGCs in the larval ovary reside in close proximity to Somatic Intermingled Cells (ICs). PGCs and ICs communicate via an Epidermal Growth Factor Receptor (EGFR)-dependent feedback loop (Gilboa and Lehmann, 2006). PGCs produce Spitz, which is required for IC survival and for the production of an unknown substance that represses PGC proliferation. To reveal the identity of this unknown substance we used microarray analysis, comparing wild-type ovaries to ovaries that express an activated form of EGFR. The microarray, together with other lines of evidence suggested one ligand emanating from ICs, is repressing PGC proliferation. Indeed, reducing the amount of this ligand in ovaries results in over-proliferation of PGCs. We are currently investigating the molecular mechanisms that underlie the repression of PGC proliferation by this ligand. We are also investigating the signals that positively control PGC proliferation. Our preliminary results suggest that the ligand Decapentaplegic (Dpp) is required for proliferation of PGCs. In the past year our lab conducted a genetic screen to identify regulators of niche formation and stem cell maintenance. The screen was based on direct observation of precociously differentiating PGCs in larval ovaries. The novel detection mode allowed us to uncover novel genes that are important for both niche formation and stem cell maintenance. We are now studying some of these regulators. Combined, our studies will lead to a better understanding of the complex relationship between stem cells and the organs they reside in. Cross talk between stem cell and niches determine the number of stem cells an organ contains, their division rate, maintenance and differentiation. Better understanding of the biological principles underlying such complex relationships is required for our understanding of normal development, disease and, possibly, its treatment.

Atan Gross: Our lab is primarily focused on studying regulatory mechanisms controlling the balance between cell life and death. In the first line of research, we are exploring the activities of the pro-apoptotic BID protein at the mitochondria by studying its interaction with a novel and uncharacterized protein named mitochondrial carrier homolog 2 (MTCH2)/Met-induced mitochondrial protein (MIMP). We have recently revealed that MTCH2/MIMP acts as a mitochondrial receptor for BID and plays a critical role in liver apoptosis. We have also found that MTCH2/MIMP is involved in mitochondria metabolism, and our future goals are to determine its exact function at the mitochondria and how it may connect apoptosis and metabolism. In a second line of research, we are exploring the activities of BID in the response of cells to DNA damage. We have previously found that DNA damage induces the phosphorylation of BID by the ataxia-telangiectasia mutated (ATM) kinase, and that this phosphorylation is important for cell cycle arrest at the S phase and for inhibition of apoptosis. More recently we have revealed that phosphorylated BID plays a critical role in protecting bone marrow cells from DNA damage, and our future goals are to determine the mechanistic details of BID's activities in the hematopoietic lineage.

Ami Navon: In both prokaryotic and eukaryotic cells, most proteins are degraded in an ATP-dependent manner. In eukaryotes ATP-dependent degradation is executed by the 26S proteasome, which hydrolyzes ubiquitin-conjugated and certain non-ubiquitinated polypeptides. Its primary function is the turnover of damaged or misfolded proteins. In addition, the proteasome affects the cell cycle and other processes through the degradation of regulatory components and transcription factors. The proteasome is important for immune system as well through processing of NFkB, a key factor in the inflammatory response, and in generating peptides used for MHC class I presentation. Furthermore, the proteasome plays a crucial role in the pathogenesis of degenerative diseases, such as Parkinson and ALS, presumably through its failure to degrade specific proteins, which form deleterious aggregates. Currently, our lab is investigating three aspects related to proteasomal degradation. The major effort of the lab is invested in understanding the molecular mechanism underlining the function of the proteasome regulatory ATPase complex, which is responsible for substrate recognition, unfolding and translocation into the 20S proteasome. In addition, we also study the significance of the N-linked-glycans removing enzyme PNGase, for the proteasome associated MHC class I antigen presentation. Recently, we became interested in the mechanistic reasons for the failure of the 26S proteasome to degrade certain substrates under specific physiological conditions. This may result in the accumulation of aggregated proteins and lead to degenerative diseases such as Parkinson and ALS. To address these scientific aims, we use an integrative approach of biochemistry, structural biology and cell biology.

Michal Neeman: Application of MRI and optical imaging for elucidation of the regulatory pathways that control the recruitment of endothelial capillaries (angiogenesis), vascular maturation, and remodeling of the lymphatics. Studies aim to reveal the contribution and interplay between environmental, hormonal and growth factor mediated signaling pathways. Specific steps in the process are detected by monitoring hemodynamic properties, vascular permeability and changes in the extracellular matrix. Vascular remodeling is followed in a range of biological models including reproduction, embryonic development, repair of ischemic injuries, tumor progression and metastatic dissemination.

Yoram Salomon: Vascular targeted photodynamic therapy (VTP) is a local anti vascular treatment modality of solid tumors that uses light and Pd-bacteriochlorophyll derivatives as photosensitizers. The anti tumor action is delivered by a local burst of cytotoxic reactive oxygen species that leads to the treatment endpoint - blood stasis within minutes and consequent tumor eradication. The mechanism of vascular destruction by VTP is the major objective of the research. Online imaging by fMRI based on photoinduced BOLD contrast is being developed as means of treatment-follow up and guidance. Intravital microscopy studies in combination with MRI aim at elucidation of the hemodynamic and photochemical basis of the BOLD contrast. The immunological response of the treated mice associated with the healing of the VTP induced injury is also being examined. This work was done in collaboration with Michal Neeman, Dept. of Biological Regulation and Avigdor Scherz, Dept. of Plant Sciences.

Rony Seger: In order to survive and perform their functions, cells need to respond to many extracellular signals such as mitogens, hormones, cytokines, physical changes of the environment and stress. In the lab we are characterizing the intracellular transmission of extracellular signals by seven distinct signaling pathways: four MAP Kinase cascades (ERK, JNK, p38 and BMK) two PI3K dependent cascades (AKT and S6K) and the PKA cascade. These studies included (i) identification of novel components, (ii) cross-talk between the distinct cascade, (iii) intracellular localization of components of the cascades, and are aimed to elucidate how the signaling network formed by these signaling cascade regulate gene expression, proliferation, and differentiation. In the last year we focused mainly on (i) the translocation of ERK and other MAPKs into the nucleus, (ii) the mechanism of AKT regulation by kinases, scaffold proteins and phosphatases (iii) the role of alternatively spliced variants of MEK and ERK in Golgi fragmentation, and (iv) antiangiogeic signaling by PEDF. These studies should shed a new light on the regulation of proliferation and survival of both normal or transformed cells.

Alex Tsafriri: Ovulation in mammals is a preferable target for contraception and fertility regulation. Our studies are focused primarily on two of the ovulatory processes: (i) Oocyte maturation, including the differential regulation and activity of phosphodiesterases and other regulators of meiosis in the germ cells and somatic compartments in the ovary). (ii) Follicular rupture at ovulation and the involvement of proteolytic cascades (plasmin activating system, and collagenases), eicosanoids and other paracrine regulators.

Eldad Tzahor: The nature of the instructions leading to a specific cell fate is one of the most puzzling questions in biology. The fates of embryonic progenitor cells and their patterning require a molecular "dialogue" between adjacent cell populations, yet the details of these molecular interactions remain elusive. For the past few years, we have focused on the characterization of signaling molecules that regulate both heart and craniofacial muscle formation during early vertebrate embryogenesis (Tzahor et al., 2003; Tzahor and Lassar, 2001). Heart and skeletal muscle progenitor cells are thought to derive from distinct mesoderm regions during early embryogenesis. The recent identification of the secondary heart field in vertebrate embryos led us to consider the contribution of the secondary heart field to cardiac development. What might be the relationship between the cranial paraxial mesoderm (the precursors of the skeletal muscles in the head) and this newly discovered myocardial lineage? Utilizing fate mapping studies, gene expression analyses, and manipulations of signaling pathways in the chick embryo, both in vitro and in vivo, we have demonstrated that cells from the cranial paraxial mesoderm contribute to myocardial and endocardial cell populations within the cardiac outflow tract. Furthermore, BMP signals, which block head muscle formation, act as potent inducers of the secondary heart field lineage (Tirosh-Finkel et al., 2006, accepted for publication). These findings support the notion that the cells within the cranial paraxial mesoderm play a vital role in cardiogenesis. Based on our past and ongoing studies, we propose that the developmental programs of progenitor populations that contribute to the head muscles and the anterior pole of the heart are tightly linked, indicative of a single cardiocraniofacial morphogenetic field.

During vertebrate craniofacial development, progenitor cells derived from the mesoderm fuse together to form a myofiber, which is attached to a specific skeletal element derived from the cranial neural crest (CNC) in a highly coordinated manner. To investigate this exquisitely tuned process, we employ both mouse genetic models and the avian experimental system to explore the molecular crosstalk between CNC and mesoderm progenitor cells during vertebrate head development. Thus far, loss- and gain-of-function experiments in both mouse and avian models demonstrate that skeletal muscle patterning and differentiation in the head are precisely regulated by CNC cells (Rinon A, Lazar S, & Tzahor E, in preparation). Our studies on cardiac and skeletal muscle specification during vertebrate embryogenesis are expected to provide valuable and original insights that may contribute to our understanding of normal as well as pathological aspects of heart and craniofacial development.

Karina Yaniv: Our lab takes advantage of the optical clarity and genetic accessibility of the zebrafish embryo to study vessel formation in vivo. Zebrafish embryos develop externally and are optically clear, providing noninvasive and high-resolution observation of the entire vascular system at every stage of embryonic development. In addition, the formation and anatomical layout of the fish vasculature are similar to that of other vertebrates, and most of the genes currently known to act as key players in embryonic vascular development are highly conserved in zebrafish. In recent years, it has become clear that many of the signals implicated in vascular development are reactivated during disease states of angiogenesis such as tissue ischemia, coronary heart disease and cancer-promoted angiogenesis. This has further reinforced the potential medical relevance of vascular development studies such as those carried out in our laboratory.

Yosef Yarden: Growth factors enable clonal expansion and fixation of genetic aberrations by ensuring unlimited proliferation of transformed cells (tumor growth), attraction of blood vessels (angiogenesis) and colonization of distant sites (metastasis). An example is provided by the family of epidermal growth factor (EGF) and the neuregulins, which bind with the ErbB family of receptors. ErbB proteins and their EGF-like ligands play essential roles in human cancer. One important mechanism involves autocrine loops comprising co-expression of a receptor and the respective ligand. Another mechanism entails genetic aberrations, which relate primarily to ErbB-1, and involve deletion of regulatory domains. Mutant forms of ErbB-1 were found in both brain and lung tumors. Last, overexpression of ErbB-2/HER2 in human carcinomas characterizes a relatively aggressive subset of mammary and other tumors. Our previous studies raised the hypothesis that an overexpressed ErbB-2 biases formation of the mitogenically more potent ErbB heterodimers, and indeed, the crystal structure of ErbB-2 revealed the existence of a dimerization loop ready to engage in dimer formation. Thus, ErbB-2 is a pre-activated receptor, which can amplify growth signals without binding to a ligand of its own.

Our biochemical analyses led us to the realization that the four ErbBs and their many ligands form a layered signaling network. Invertebrates like C. elegans and Drosophila, present simple versions of the network, which gradually evolved complexity through gene duplications and genetic diversification. The layered structure of the mammalian network ensures robust signaling, while maintaining stringent control and finely tuning the output. Once activated by growth factors, receptor tyrosine kinases simultaneously launch both 'positive signals', which lead to cell stimulation, and delayed 'negative signals', which regulate the amplitude and duration of these positive signals. A delicate balance between positive and negative signals is critical for normal cellular homeostasis, and its disturbance is often implicated in disease development. Hence, we focused our studies on negatively acting pathways that normally desensitize growth factor signaling. Our studies of the last few years identified several negative regulatory pathways, such as ligand-induced receptor endosytosis and degradation, as well as induction of newly synthesized negative regulators of the network, which are defective in human tumors of epithelial origin. In the last year we focused on additional potential mechanisms that restrain ErbB signaling in normal cells, but whose function may be aberrant in tumors. The list of potential regulators includes transcription repressors, MAPK and tyrosine-specific phsospatases, de-ubiquitination enzymes, micro-RNA molecules and alternatively spliced forms of growth factor-induced mRNAs. Interestingly, many actin-binding proteins are included in the group of late-induced, growth factor up-regulated transcripts. Our initial studies uncovered involvement of these mRNAs in growth factor-induced cell migration and invasion, observations we hope to extend to metastasis driven by the ErbB family of receptors and their EGF-like ligands. 

Research Staff, Visitors and Students


Hadassa Degani, Ph.D., State University of New York, Stony Brook, United States (on extension of service)
       The Fred and Andrea Fallek Professorial Chair in Breast Cancer Research
Nava Dekel, Ph.D., Tel Aviv University, Tel-Aviv, Israel
       The Philip M. Klutznick Professorial Chair of Developmental Biology
Michal Neeman, Ph.D., Weizmann Institute of Science, Rehovot, Israel
       The Helen and Morris Mauerberger Professorial Chair in Biological Sciences
Yoram Salomon, Ph.D., The Hebrew University of Jerusalem, Jerusalem, Israel (on extension of service)
       The Charles W. and Tillie K. Lubin Professorial Chair of Hormone Research
Rony Seger, Ph.D., Weizmann Institute of Science, Rehovot, Israel
       The Yale S. Lewine and Ella Miller Lewine Professorial Chair for Cancer Research
Yosef Yarden, Ph.D., Weizmann Institute of Science, Rehovot, Israel
       The Harold and Zelda Goldenberg Professorial Professorial Chair in Molecular Cell Biology

Professor Emeritus

Alexander Tsafriri, Ph.D., Weizmann Institute of Science, Rehovot, Israel

Associate Professor

Atan Gross, Ph.D., The Hebrew University of Jerusalem, Jerusalem, Israel

Senior Scientists

Lilach Gilboa, Ph.D., Tel Aviv University, Tel-Aviv, Israel
       Incumbent of the Skirball Career Development Chair in New Scientists
Ami Navon, Ph.D., Bar-Ilan University, Ramat-Gan, Israel
       Incumbent of the Recanati Career Development Chair of Cancer Research
Eldad Tzahor, Ph.D., Weizmann Institute of Science, Rehovot, Israel
       Incumbent of the Gertrude and Philip Nollman Career Development Chair
Karina Yaniv, Ph.D., The Hebrew University of Jerusalem, Jerusalem, Israel

Senior Staff Scientist

Batya Cohen, Ph.D., Weizmann Institute of Science, Rehovot, Israel

Senior Interns

Erez Moshe Bublil, Ph.D., Tel Aviv University, Tel-Aviv, Israel (left July 2010)
Hagit Dafni, Ph.D., Weizmann Institute of Science, Rehovot, Israel
Moshit Lindzen, Ph.D., Weizmann Institute of Science, Rehovot, Israel
Zhong Yao, Ph.D., Weizmann Institute of Science, Rehovot, Israel


Efrat Glick-Saar, Ph.D., Bar-Ilan University, Ramat-Gan, Israel (left October 2010)


Amichai Barash, Kaplan Medical Center, Rehovot, Israel (left June 2010)
Catherine Brami, Tel Aviv University, Tel-Aviv, Israel
Irit Granot, Kaplan Hospital, Rehovot, Israel
Fortune Kohen
Alexander Konson (left May 2010)
Ariel Rinon
Yael Schiffenbauer, Aspect-Magnet, Netanya, Israel
David Varon, Hadassah Medical Center, Jerusalem, Israel (left January 2010)

Visiting Scientists

Avner Baz, Tufts University Medford,MA, U.S.A.
Yonni Cohen, Tel Aviv Sourasky Medical Center, Israel
Yehia Daaka, MIT, Mass. Inst. of Tech., U.S.A.
Joel Garbow
Sebastian Katz
Philip Tickhock Lee, Singapure Bioimaging onsorium, Singapore
Guy Nadel
Deborah Schechtman
Tal Shapira - Roten
Zhong Yao

Postdoctoral Fellows

Nira Amar, Ph.D., Weizmann Institute of Science, Israel
Inbal Avraham-Davidi, Hebrew University of Jerusalem, Israel
Vardina Bensoussan, Pasteur Institute (Paris)
Pradeep Chaluvally Raghavan, Ph.D., Amala Cancer Research Centre, Kerala, India
Cosimo Walter D'Acunto, University of Salerno
Anna Maria Emde, M.D.
Dana Gancz, Tel-Aviv University, Israel
Miriam Ivenshitz, Ph.D., Weizmann Institute of Science, Israel
Edith Kario, Weizmann Institute of Science, Israel
Merav Kedmi, Tel-Aviv University, Israel
Alexander Konson, Ph.D., Ben-Gurion University, Israel
Mattia Lauriola, Bologna University
Iris Maimon (Edry), Ph.D., Weizmann Institute of Science, Israel
Guy Malkinson, Hebrew University of Jerusalem, Israel
Elisha Nathan, Weizmann Institute of Science, Israel
Alexander Plotnikov, Tel-Aviv University, Israel
Sunila Pradeep, Ph.D., Amala Cancer Research Centre, Kerala
Marina Radoul, Weizmann Institute of Science, Israel
Tal Raz, M.D., Western College of Veterinary Medicine, University
Ariel Rinon, Weizmann Institute of Science, Israel
Stav Sapoznik, Weizmann Institute of Science, Israel
Hagit Schayek, Tel-Aviv University, Israel
Nilly Shimony, Hebrew University of Jerusalem, Israel
Ketty Shkolnik, Weizmann Institute of Science, Israel
Assaf Tal, Weizmann Institute of Science, Israel
Moriel Vandsburger, University of Virginia
Michal Weiler-Sagie, Ben-Gurion University, Israel
Natalie Yivgi-Ohana, Ph.D., Hebrew University of Jerusalem, Israel
Yaara Zwang, Weizmann Institute of Science, Israel

Research Students

Yoseph Addadi Reut Avni
Roi Avraham Avital Beer
Nir Ben-Chetrit Dikla Berko
Yinon (Yoni) Cohen Adva Cohen Fredarow
Hadas Cohen-Dvashi Yael David (Ben-basat)
Judith Elbaz Erez Eyal
Liron Gibbs Bar Itai Glinert
Itamar Harel Anna Hitrik
Edith Kario Wolfgang Koestler
Tamar Lengil Minjun Li
Noa Madar-Balakirski Maria Maryanovich
Inbal Michailovici Michal Milgrom-Hoffman
Galia Oberkovitz Roni Oren
Adi Pais Fresia Gilda Pareja Zea
Gur Pines Gregory Jacques Ramniceanu
Shiri Raphaelli-Procaccia Yitzhak Reizel
Stav Sapoznik Aldema Sas-Chen
Liat Shachnai Yael Shahar-Pomerantz
Helena Sheikhet-Migalovich Ketty Shkolnik
Ari Tadmor Gabi Tarcic
Yael Chagit Tzuman Katrien Vandoorne
Jean Wakim Inbal Wortzel
Yfat Yahalom - Ronen Eldar Zehorai


Rachel Benjamin