Dopamine neurons and the innervation of their targets mediate complex behaviors and their degeneration or aberrant function underpins Parkinson's disease and schizophrenia. My lab investigates how dopamine neuron circuits develop, how & when the loss of dopamine neurons of a distinct genetic lineage affects brain function, mechanisms of specifying/maintaining dopamine neurons and cell-based therapies to ameliorate deficits in genetically altered mice with features of neurological disorders.

Biography

While studying pyramidal neurons differentiation and cortical development, I fortuitously showed that ectopic dendrite growth in metabolic brain disorders was accompanied by intra-neuronal cholesterol and ganglioside accumulation. I subsequently designed a therapeutic approach that ameliorated neuropathology in animal models of Niemann-Pick Disease Type C. This led to an ongoing clinical trial and sparked my interest in brain development and disease.

I am using Genetic Inducible Fate Mapping to forge a link between gene expression during embryogenesis and the behavior of cells during brain development. This method revealed that the Wnt1 lineage contributes to midbrain dopaminergic neurons. I then showed that Wnt1 is required for subpopulations of dopaminergic neurons that mediate movement and cognition; I am now evaluating the pathological and behavioral correlates in these mice, which may be relevant to Parkinson's disease and schizophrenia.

I am using state-of-the-art genetic approaches to investigate dopaminergic neuron development, the relationship between genetic lineage and dopamine neuron circuitry and how perturbations in these events may contribute to neurological diseases.

Research Description

Overview of Research Interests
In the broadest sense I am interested in early developmental mechanisms that shape the brain and how these events can be exploited to understand neurological diseases.

A central problem in Developmental Neurobiology is how are relatively simple neuroepithelial tissues patterned and organized during embryogenesis to become highly organized anatomical and physiological structures like the brain? An equally important problem in Neurological Disease is what are the aberrant genetic and cellular events that underpin distinct pathological features of brain disorders. My lab uses sophisticated Genetic approaches in mouse to understand these seemingly unrelated disciplines implicit with the idea that unraveling and intervening in complicated disorders requires understanding how genetic identity is regulated during development, knowing the cell behaviors involved in brain morphogenesis, as well as having insight into how neurons of the brain are specified and the connections to their targets established. In short, knowledge of developmental events may prove beneficial to understanding neurological diseases.

Background and Significance Underpinning my Research Interests
Multiple types of neurons and neural circuits are coordinated to execute a complex array of tasks executed by the brain. In particular, midbrain dopaminergic (MbDA) neurons of the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) have axons that project over long distances to integrate spatially disparate regions into distinct functional units (circuits). MbDA neuron circuits mediate motor behaviors and cognition and their degeneration or aberrant function has profound pathological consequences such as motor abnormalities accompanying Parkinson's disease or cognitive deficits associated with schizophrenia. The loss of MbDA neurons of the SNc is a central feature of Parkinson's disease. In contrast, the identification of a single substrate underpinning the pathophysiology of schizophrenia has remained elusive, although experimental and clinical pharmacology data strongly suggest that the dopamine system is also the fulcrum of schizophrenia. Of particular interest are the MbDA neurons of the VTA, which innervate the dorsal lateral pre-frontal cortex (DLPFC) and ventral striatum. VTA DA neurons are intricately involved in behaviors including motivation, reward, and cognition. Deficiencies in VTA DA neurons appear to contribute to a broad array of cognitive disorders including schizophrenia. These observations have led to a dopamine-centric hypothesis of schizophrenia that is often coupled with a supposition of developmentally dysregulated DA neuron circuitry. However, such potential developmental defects have not been validated experimentally. In addition, the genetic lineage and developmental mechanisms defining VTA and SNc DA neurons have not been determined. Elucidating the mechanisms that link the genetic lineage of MbDA neuron sub-populations to precise circuit formation in vivo is essential to understand brain development and to gain insight into neurological disorders such as Parkinson's disease and schizophrenia.

I previously used GIFM to show that Wnt1-derived progenitors give rise to MbDA neurons in vivo using Wnt1-CreER;R26R mice. GIFM permanently and heritably marks small populations of progenitors and their descendants using a modified Cre/loxP system and a conditional LacZ reporter allele encoding ß-galactosidase, which marks cell bodies. In GIFM, precise temporal control of recombination (marking) is achieved by inducible Cre recombinase (CreER) while spatial control is obtained by region specific gene regulatory elements. I established that cells expressing Wnt1 during embryogenesis give rise to different populations of Mb neurons in vivo. Specifically, between embryonic day (E)8.5-11.5 the Wnt1-lineage contributes to MbDA, but not cholinergic, or serotonergic neurons. However, how and when neurons of a distinct genetic lineage are organized into functional circuits in unknown.

Specific Aims to Test my Research Interests
The central purpose of this my research interests is to understand how neurons derived from precursors expressing specific genes (genetic lineage) at distinct times are organized into functional circuits. The central hypothesis of underpinning my research interests is that: Genetically-defined VTA and SN dopaminergic neurons project their axons to specific target sites at distinct time points to generate precisely organized functional circuits. The specific aims are:

I. Determine when Wnt1-derived dopaminergic neurons establish VTA and SN circuitry in vivo.
Hypothesis: The Wnt1 lineage at specific time points gives rise to VTA and SNc dopaminergic neurons that project to distinct targets.
Experiments: Genetic Inducible Fate Mapping (GIFM) to establish a map of dopaminergic circuitry in vivo.

II. Establish how Mb dopaminergic neurons assemble into distinct nuclei in vivo.
Hypothesis: Cohorts of genetically-related dopaminergic neurons are organized within distinct domains and this organization is reflected in their target field.
Experiment: Dual GIFM to uniquely mark cohorts of Wnt1-derived dopaminergic neurons as they form Mb nuclei and project to their target(s).

III. Ascertain how and when the loss of dopaminergic neurons of the Wnt1 lineage during development and in the adult impacts on dopamine circuitry in vivo.
Hypothesis: The loss of genetically-related VTA dopaminergic neurons in development versus the adult differentially affects the VTA dopaminergic circuitry.
Experiments: Genetic ablation of Wnt1-derived dopaminergic neurons and analysis of targeted domains.

IV. Determine the role of Wnt1 in specifying/maintaining Mb dopaminergic neurons in vivo.
Hypothesis: Wnt1 specifies dopaminergic neuron phenotype and is required at specific time points.
Experiments: GIFM on Swaying mutant background and conditional inactivation of Wnt1.

Future Directions of my research Interests
* Hypothesis: Dopaminergic neuron degeneration can be rescued with cell-based strategies.
Experiment: Stem cell transplantation of Wnt1-derived dopaminergic progenitors into Swaying mice.

The above specific aims will determine how neurons of distinct lineages are specified, assembled into organized anatomical domains, and form functional units in vivo. I will determine the functional significance of genetically defined circuits implicated by evaluating physiological and behavioral changes in mice with genetically ablated sub-populations of Wnt1-derived MbDA neurons, in mice with a genetic (point) mutation in Wnt1 (Swaying mice) and in Wnt1 conditional knockout mice. This type of comprehensive approach will be critical in understanding how to re-build these networks in a disease treatment context. Toward this goal, I will evaluate the efficacy of cell-based therapies in regenerating depleted populations of MbDA neurons in Swaying mice as a model system. First, I will evaluate whether Wnt1-derived neuronal precursors marked at specific time points can be isolated, expanded in vitro, and transplanted - with the goal of determining if they efficiently integrate into the ventral Mb of mice. This will be done at developmental stages (determined in the above specific aims) and in the adult to ascertain when integration is most effective at repopulating depleted DA neurons. Importantly, I will assess whether stem cell integration has led to meaningful temporal and spatial recapitulation of relevant MbDA neuron circuitry (determined in specific aims II and III) by virtue of the eGFP reporter allele as well as to an improvement in behavioral deficits.

Awards

Manning Assistant Professorship
NIH Ruth L. Kirschstein National Research Service Award (F32HD43533)
Thesis Departmental Honors
Pre-Doctoral Fellowship (NS07098)
Department of Neuroscience Travel Award

Affiliations

Member, Society for Developmental Biology
Member, Society for Neuroscience

Funded Research

Completed Research Support
2003-2006 NIH Ruth L. Kirschstein National Research Service Award (F32HD43533; $150,000)
Title: Lineage Restriction and Development of the Midbrain and Cerebellum.
The goal of this project was to test the following central hypotheses: 1. Lineage restriction and compartmentalization partition the central nervous system into distinct functional units; 2. Wnt1 maintains the lineage boundary between the midbrain and cerebellum; 3. Wnt1 has a temporally diverse role in midbrain development; 4. Progenitor cells of distinct lineage give rise to specific types of neurons in vivo.

Active Research Support
2007-2008 The Rhode Island Foundation Research Award (20070265; $10,000)
Title: Genetic Neuroanatomy of Substantia Nigra Dopamine Neurons
The goal of this project is begin to: 1. Establish how the diversity of dopaminergic neuron sub-populations is esablished; 2. investigate the role of Wnt1 in this process; 3. ascertain how genetic lineage relates to dopaminergic neuron circuitry.

Submitted Research Support
Brown COBRE
R21

Teaching Experience

Instructor for CSHL Course on Stem Cells

Lecturer & discussion leader for Boundaries and Compartments lecture, Foundations in Developmental Genetics Course, Skirball Graduate Curriculum

Lecturer for Mouse Genetics lecture, Eukaryotic Genetics Course, Skirball Graduate Curriculum

Mentor to 3 graduate students in three month-long rotations, Developmental Genetics Graduate Program

Mentor to undergraduate student in NYU/Sackler Institute Summer Undergraduate Research Program

View My Full Publication List in pdf format

Selected Publications

• Joyner AJ, Zervas M (2006) Genetic Inducible fate mapping in mouse: establishing genetic lineages and defining genetic neuroanatomy in the nervous system. Dev. Dynamics 235:2376-2385.(2006)
• Zervas M, Joyner AJ (2006) Developmental neurogenetics of murine dopaminergic and serotonergic neurons in vivo. Neuron (manuscript in preparation).(2006)
• Zervas M, Opitz T, Edelmann W, Wainer B, Kucherlapati R, Stanton P (2005) Impaired Hippocampal Long-Term Potentiation (LTP) in Microtubule-Associated Protein 1B-deficient Mice. J. Neurosci. Res. 82:83-92.(2005)
• Zervas M, Blaess S, Joyner AJ (2005) Classical embryological studies and modern genetic analysis of midbrain and cerebellum development. Curr. Topics Dev. Biol., (Neural Development), 69:101-138. Invited review, selected scientific image featured on cover.(2005)
• Zervas M, Millet S, Ahn S, Joyner AJ (2004) Cell behaviors and genetic lineages of the mesencephalon and rhombomere 1. Neuron 43:345-357.(2004)
• Zervas M, Dobrenis K, Walkley SU (2001) Neurons in Niemann-Pick disease type C accumulate gangliosides as well as unesterified cholesterol and undergo dendritic and axonal alterations. J. Neuropathol. Exp. Neurol. 60(1):49-64.(2001)
• Zervas M, Somers KL, Thrall MA, Walkley SU (2001) Critical role for glycosphingolipids in Niemann-Pick disease type C. Curr. Biol. 11(16):1283-1287.(2001)
• Walkley SU, Zervas M, Wiseman S (2000) Gangliosides as modulators of dendritogenesis in normal and storage disease-affected pyramidal neurons. Cereb. Cortex 10(10):1028-1037.(2000)
• Zervas M and Walkley SU (1999) Ferret pyramidal cell dendritogenesis: changes in morphology and ganglioside expression during cortical development. J. Comp. Neurol. 413(3):429-448.(1999)
• Walkley SU, Siegel DA, Dobrenis K, Zervas M. (1998) GM2 ganglioside as a regulator of pyramidal neuron dendritogenesis. Annals of the NY Academy of Science 845:188-199.(1998)
• Edelmann W, Zervas M, Costello P, Roback L, Fischer I, Hammarback JA, Cowan N, Davies P, Wainer B, Kucherlapati R (1996) Neuronal abnormalities in microtubule-associated protein 1B mutant mice. Proc. Natl. Acad. Sci. USA 93:1270-1275.(1996)