Name Marten P. Smidt
Department Neuroscience and Pharmacology
Section Neurodevelopment
Function Professor
E-mail:
m.p.smidt-2@umcutrecht.nl
Telephone number:+31 88 7568809
Research group PhD students 2004-2008: Frank Jacobs (PhD student): Identification of target genes of the homeodomain gene Pitx3 (HIPO project)
2007-2011: Teresa Alves Dos Santos: Identification of Pitx3 regulated genes in midbrain dopamine neurons (ALW project)
2007-2011: Elisa Hoekstra: Molecular coding of mdDA neurons during development (TIP project)
Postdocs 2008-2012: Koushik Chakrabarty, Molecular programming of mdDA neurons, TIP project.
Vacancy (EU project)
Technicians
Lars von Oerthel (100%)
Annemarie van der Linden (100%)
Raymond Schellevis (50%)
Summary research
My main interest is molecular programming during development of the central nervous system. Since at that time almost nothing was known on the subject, I started with JPH Burbach a cloning effort to identify transcription factors that play a role during CNS development. From this work three major breakthroughs were established:
1. The cloning, identification and characterization of the homeobox gene Pitx3. This gene was found to be exclusively expressed in the substantia nigra (SNc) and ventral tegmental area (VTA) forming the midbrain dopamine system, essential for mood and movement regulation in mammals. The real impact of the work was that this factor is exclusively expressed in these neurons and this formed the first step in the understanding of molecular programming of midbrain dopamine neurons.
2. The identification of the role of the orphan nuclear hormone receptor Nurr1. It was shown by us and others that Nurr1 is essential for the development of fully differentiated midbrain dopamine neurons. This was the second factor identified to be involved in midbrain dopamine neurodevelopment.
3. The identification of Lmx1b. We showed that the early specification of the midbrain by Lmx1b is essential for the formation of midbrain dopaminergic neurons. Moreover, we showed that TH expression was possible in early DA neurons without the expression of Pitx3, indicating that Pitx3 might be involved in molecular processes other than transmitter phenotype.
After this cloning and descriptive phase I was interested to go into depth into the role of Pitx3 (as an NWO fellow) in the neurodevelopment of midbrain dopamine neurons and to broaden my view on molecular signaling events in neuronal cells. This was accomplished by the start of analysis of the Pitx3 knock out and by the start of a new research line on forkhead proteins (FoxO and FoxK family). The work lead to three major findings:
1. The data from the Pitx3 knock-out analysis (aphakia mouse) formed a new chapter in the understanding of the role of Pitx3 in the development of midbrain dopamine neurons. We showed that Pitx3 is essential for the formation of the SNc and the ventral part of the VTA. Moreover it was clear from the analysis that the defect was apparent at the early stage of terminal differentiation, Most importantly, the defect was not present in all midbrain dopamine neurons but mainly in the ventral medial SNc and ventral VTA.
2. The cloning and functional characterization of FoxO6, a novel member of the FoxO family (FoxO1, FoxO3 and FoxO4). We showed that FoxO6 had unique properties in terms of nucleo-cytoplasmic shuttling, as a result of PKB signaling, compared to its family members. Later we showed the mechanism of the altered shuttling behavior and showed that phosphorylation by PKB does inactivate FoxO6 by inhibiting DNA interaction without the extra level of inhibition of nuclear removal (publication ). We have gained quickly a good position by this work. A review from our team received much enthusiasm as highlighted by 82 citations so-far and the 25th place of most downloaded papers in the publication year.
3. The identification a novel factor of the FoxK family, namely (mouse) Foxk2. This factor was, based on sequence homology, the designated orthologue of yeast Fkh2 which is essential in the progression of the cell-cycle (G2/M phase progression). Our analysis showed that the functional similarity is not apparent, Foxk2 has a function in cell-survival but does not stimulate the G2/M phase transition.
The fact that a subset of the complete group of dopamine neurons was affected in the Pitx3 knock-out (Pitx3 itself is expressed in all midbrain dopamine cells) initiated the novel idea that the molecular coding of the SNc and VTA is not the same. A real step forward was made by the identification of subset specific markers and coding differences in the ventricular zone. This concept of subset specification was a crucial step in the way the field regarded the molecular pathways leading to the development of dopamine neurons of the SNc and VTA. In addition, it became clear that the neurons populating the SNc and VTA are not generated exclusively in the midbrain but also in the diencephalon. Therefore, the name of this neuronal group was changed to mesodiencephalic dopaminergic (mdDA) neurons and has been used as such from that point on.
This was a crucial moment in my career, i established my own group and my work clearly surpassed the initial identification and function-description of transcription factors involved in the development of mdDA neurons. My interest went into two additionally research directions:
1. The live visualization of dopamine neurotransmission through multi-pinhole SPECT. Prof dr. Freek Beekman designed a spectacular micro-SPECT system to follow tracers in the mouse brain with a resolution of 0.3 mm. Together we started to image live dopamine transmitter events in a living mouse.
2. Understand how subset specification is established, which subsets exist and what the relationship is between subset and specific connectivity. A crucial finding in the understanding of subsets specific molecular coding was established through the identification of a subset specific transcriptional target of Pitx3. This gene, (retinal) aldehyde dehydrogenase 2 (Ahd2, Raldh1) is expressed, in the adult brain, in the ventral cells of the SNc and VTA, the neurons that are lost in the Pitx3 mutant. A second novel finding was that retinoic acid (RA) has a role in terminal differentiation of this specific set of neurons in addition to its role in the ventricular zone. Ahd2 is present in ventricular zone cells, its transcription is terminated when cells leave the ventricular zone and under the control of Pitx3, Ahd2 is transcribed again in a (lateral) subset of mdDA neurons and is essential for the synthesis of RA out of retinal. We were able to show the dependence of mdDA differentiation for RA signalling by rescuing the Pitx3 knock-out phenotype through the exogenous application of RA.
Although I am still working on- and interested in the FoxO6 knock out (we have generated chimeric animals) my main interest lies with the molecular programming of mdDA neuronal subsets. My lab is currently investigating 1) why Ahd2 activation is only happening in the described subset; 2) we are mapping transcriptional targets of Engrailed, Lmx1a/b, and Nurr1 to get a better idea about the molecular programming that is initiated within mdDA neurons; 3) the functional interaction between Pitx3/Nurr1 and En1 and 4) we are finalizing the identification of adult subset specific markers. At this moment my research group consist of 3 PhD students, 2 technicians and every year about 3 master students.
The work described above has been very fruit-full and has lead to a leading position of my research group mainly in the field of development and engineering of mdDA neurons, marked by many invitations to write reviews/books on the topic, the high amount of peer-reviewed publications and the invitations to speak at the international level about my work.
Publications Smits SM, Noorlander CW, Kas MJ, Ramakers GM, Smidt MP. Alterations in serotonin signalling are involved in the hyperactivity of Pitx3-deficient mice. Eur J Neurosci. 2008 Jan;27(2):388-95. PMID: 18215235, IP 4.2
Jacobs FM, Smits SM, Noorlander CW, von Oerthel L, van der Linden AJ, Burbach JP, Smidt MP. Retinoic acid counteracts developmental defects in the substantia nigra caused by Pitx3 deficiency. Development. 2007 Jul;134(14):2673-84. PMID: 17592014, IF 8
Smidt MP*, Burbach JP. How to make a mesodiencephalic dopaminergic neuron. Nat Rev Neurosci. 2007 Jan;8(1):21-32. Review. PMID: 17180160 * corresponding author, IF 23
Smits SM, Burbach JP, Smidt MP. Developmental origin and fate of meso-diencephalic dopamine neurons. Prog Neurobiol. 2006 Jan;78(1):1-16. Epub 2006 Jan 18. Review. PMID: 16414173 IF 12
Smits SM, Mathon DS, Burbach JP, Ramakers GM, Smidt MP. Molecular and cellular alterations in the Pitx3-deficient midbrain dopaminergic system. Mol Cell Neurosci. 2005 Nov;30(3):352-63. Epub 2005 Sep 6. PMID: 16140547 IF 3.8
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