Patrik Ernfors Group
Program 1. Molecular mechanism of stem cell self-renewal
The self-renewing nature of stem cells is a consequence of their ability to proliferate indefinitely while maintaining pluripotency. Mechanisms of pluripotency are well known but mechanisms controlling stem cell proliferation are unknown. Control of proliferation of somatic cells takes place in G1 cell cycle phase. We have identified that embryonic and peripheral neural stem cell proliferation is regulated by an entirely new mechanism involving chromatin remodeling and operating in the S/G2 phase of the cell. This involves the DNA damage response (DDR) pathway proteins. The DDR pathway is activated physiologically by GABA acting by the GABAA receptor leading to Cl- influx, cell swelling, and by unknown mechanism, activation of the PI3K related kinases ATR/ATM which phosphorylates histone H2AX. Combined, the data suggests that the DDR pathway is operating in a ligand-dependent manner under normal physiological conditions and that it may serve as a new molecular mechanism regulating cell proliferation in mammalian cells. Based on these data we propose a homeostatic mechanism of stem cell proliferation where negative feedback control of the cell cycle adjusts stem cell numbers. The demonstration of normal, physiological, ligand-induced activation of these pathways in stem cell niches opens fundamentally new insight into the mechanisms of stem cell proliferation and surveillance against cancer. We are working to identify new adult stem cell niches and cancer stem cell populations that share this cell cycle control and determine the biochemical and molecular mechanisms. Once characterized, we propose that these mechanisms may be exploited to induce self repair following brain damage and to manipulate cell survival in tumor initiating cells.
Program 2. Molecular mechanism of neuronal specification and cell differentiation in development
Ernfors lab studies the genetic and epigenetic control of cell-type specification and differentiation during development. We study how external signals are coordinated with cell competence to generate different types of sensory neurons and how these establish functional connections with the CNS and the signals.
In particular, we are interested to understand how progenitor cells are driven to adopt a specific fate among the many possible fates during nervous system development. The neural crest is technically and conceptually an ideal model system to resolve this question. The principle of cell fate commitment involves patterning morphogens initiating cascades of combinations of transcription factors that together control cell programs. Both induction of the neural crest in the neural plate and segregation of postmigratory neural crest to different neural crest lineages are under strict control in a temporo-spatial manner by the expression of signals in adjacent somites folding into dermamyotomes and in spinal cord. By changing their competence to respond to an extrinsic signal, cells are able to diversify the possible outcomes of a given signaling pathway. This is likely to occur through changes in the complement of receptors and transcription factors (intrinsic, cell-autonomous components) that are expressed by the cell at any given time and in the way in which these interact with elements from the signaling pathways. We are also interested to understand how genetic and epigenetic signals integrate during cell differentiation. Integration can occur at the promoters of target genes or by the formation of multiprotein complexes between genetically and epigenetically controlled factors. Finally, we are interested in understanding how gene programs directing neuronal diversification are integrated with those determining the establishment of specific points of axonal projections and contacts in the central nervous system underlying development of a functional circuit. We have identified sets of key transcription factors participating in these processes and use cell/molecular tools as well as defined functional assay systems including mouse and chick genetics that combined can dissect in fine detail resolve the mechanisms behind these developmental processes.
Program 3. Basic functions, intracellular signaling and molecular mechanisms of the receptor tyrosine kinase Ret
There are several hundred tyrosine kinases in the genome. The receptor tyrosine kinases engage a limited number of intracellular mediators of signal transduction. Despite the activation of the same signaling pathways by the receptors they can deliver very different functional outcome on responsive cells. We are interested in understanding the mechanisms that confer specificity of receptor tyrosine kinases. Ret is a tyrosine kinase receptor. Ret mediates the anti-apoptotic and mitogenic signals the glial cell line derived neurotrophic factor (GDNF) family of ligands consisting of four members: GDNF, neurturin (NTN), persephin (PSP) and artemin (ART). Activation of Ret is crucial for neuronal survival of parasympathetic neurons, neural crest migration of sympathetic progenitors, proliferation by enteric neurons, neurite growth, kidney organogenesis and formation of spermatogonia. The multiple cellular functions of Ret in different populations of cells make the receptor an advantageous model system to resolve specificity in receptor signaling and open for identification of signaling pathways selectively participating in the different cellular functions of Ret. Receptor activation in oncogenic forms of Ret and following ligand engagement of normal Ret leads to autophosphoryaltion of the cytoplasmic tyrosine residues that recruit a diverse group of signalling partners including Shc, Frs2, IRS1, Dok1 to tyrosine (Y)1062 and PLC? to Y918 leading to activation of several signaling events including Ras/ERK, PI3K/Akt, JNK, CREB, PKC; IP3 and more. The Ret functions including neural progenitor migration, survival, proliferation, neurite growth/turning and cancer are mediated by binding of these adaptor molecules to tyrosine 1062, 1096 and other Y of Ret. What is the role of Ret in the postnatal mouse and what is the structural relationship between different isoforms of Ret and PTB domain adaptor binding to Ret? In particular how do they relate to function in vitro and in vivo? These are the main questions we focus on using biochemistry, in vitro functional assays and in vivo gene targeting strategies.
|Laura Calvo Enrique||Associated|
|Daohua Lou||Research assistant on study grant|
|Jana Sontheimer||Laboratory engineer|
|Dmitry Usoskin||Senior lab manager|