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Washington University in St. Louis - School of Medicine
Department of Developmental Biology

Kristen Kroll, Ph.D.

Associate Professor

Washington University School of Medicine
Campus Box 8103
660 South Euclid Avenue
St. Louis , MO 63110
(314) 362-7045

Links

Research Description

Our research focuses on defining gene regulatory networks (GRNs) that control neural cell specification, neurogenesis, and the generation of specific neuronal cell types. We are particularly interested in understanding how epigenetic regulation modulates these networks and how their dysregulation contributes to neurodevelopmental disorders, including inherited epilepsies, autism spectrum disorder, and neural tube defects. This work uses directed differentiation of human pluripotent stem cells (embryonic stem cells and induced pluripotent stem cells), mouse models, and a wide range of cellular, molecular, and genomic approaches, to define roles for transcriptional and epigenetic regulation in shaping developmental transitions.


Gene regulatory networks in neural cell fate acquisition

Figure 1. Genome-wide binding profiles for Geminin and Zic1 were used to define gene regulatory networks in neural cell fate acquisition. (A-D) Comparison of Gmnn-associated and Zic1-associated genes in NE. (A) A subset of genes is associated with both Gmnn and Zic1. p-value (Chi-square test with Yates’ correction) < 2.2X10-16. (B) z-scores for enrichment of expression in ES versus CNS tissues for all Zic and/or Gmnn associated genes. (C) Comparison of all Gmnn or Zic1 associated genes, subsets that undergo Gmnn-dependent acetylation, and transcription factors, with their relative enrichment of expression in embryonic CNS tissues. (D) GO enrichment analysis for associated genes with increased versus decreased expression in embryonic CNS, relative to ES cells. (E) Gene regulatory networks in neural cell fate acquisition. Gmnn- and Zic1-associated genes in NE that encode transcription factors and epigenetic regulatory activities were assessed for co-association with Sox2 and Sox3 in ES-derived NE (see text). The set of these genes that exhibit CNS-enriched expression (>two-fold greater expression in E14 CNS, relative to ES cells), and were associated with Gmnn and/or Zic1 plus Sox2 and/or Sox3 were used to build gene regulatory networks showing associations.


Neural cell fate acquisition is mediated by transcription factors expressed in nascent neuroectoderm, including Geminin and members of the Zic transcription factor family. Recently, we identified chromatin association profiles for Geminin and Zic1 during neural fate acquisition at a genome-wide level (Sankar et al., 2016). We determined how Geminin deficiency affected histone acetylation at gene promoters during this process. We integrated these data to determine that Geminin associates with and promotes histone acetylation at neurodevelopmental genes, while Geminin and Zic1 bind a shared gene subset. Geminin- and Zic1-associated genes exhibit embryonic nervous system-enriched expression and encode other regulators of neural development. Both Geminin and Zic1-associated peaks are enriched for Zic1 consensus binding motifs, while Zic1-bound peaks are also enriched for Sox3 motifs, suggesting co-regulatory potential. Accordingly, we found that Geminin and Zic1 could cooperatively activate the expression of several shared targets encoding transcription factors that control neurogenesis, neural plate patterning, and neuronal differentiation. We used these data to construct gene regulatory networks underlying neural cell fate acquisition. Establishment of this molecular program in nascent neuroectoderm directly links early neural cell fate acquisition with regulatory control of later neurodevelopment.
We are characterizing how disruption of this network contributes to the etiology of neural tube defects (NTDs) and other neurodevelopmental disorders. Although NTDs are the second most common birth defect (~1:1000 fetuses and newborns), their causation is poorly understood. This is, in part, because NTD occurrence usually has a multi-factorial etiology, with both genetic and environmental susceptibility factors contributing to phenotypic manifestation and severity. Therefore, defining aspects of this regulatory network that are dysregulated to contribute to NTDs in multiple models may identify core processes that, when disrupted, increase NTD susceptibility. This work also defined novel epigenetic regulators with likely roles in neural development, some of which we are functionally assessing in ongoing work.


Modeling human cortical interneuron development and dysregulation in neurodevelopmental disorders

Figure 2. Human cortical interneuron derivation and characterization. (A) Immunocytochemistry (ICC) for ventral telencephalic/MGE, neuron, cIN and alternate cell fate (RAX/DARPP32) markers, in day 35 hESC-derived interneurons (scale bar=100µm). (B) FACs for Nkx2-1 and (C) quantitation of % ICC+ cells. Inset: FACS analysis for the SST+ cortical interneuron subtype. (D) Synapsin-GFP expressing day 35 cIN (after PSA-NCAM+ selection; scale bar=100µM) were (E) transplanted into the cortex of P2 NOD/SCID mice (20 days post-transplantation shown; B’ box in B, scale bar=100µM) or (F) transplanted into the hippocampus (CA3) of NOD/SCID adult mice (1 month post-transplantation shown, C’ box in C; scale bar=50µM). (D-E) Representative action potential firing pattern (G) evoked by injection of a square pulse, (H) spontaneous. (I) Voltage-gated currents evoked by a step from -80 to +50 mV in the absence (black) or presence (red) of the sodium channel antagonist tetrodotoxin (TTX, 0.5 µM). (J) Spontaneous synaptic currents recorded at -20 and -80 mV. Exposure to the GABAA receptor antagonist bicuculline methiodide (200 µM), indicated by the open box above each trace, blocked spontaneous Inhibitory postsynaptic currents (IPSCs). IPSCs were inward at -80 mV and outward at -20 mV, consistent with the equilibrium potential for chloride (-54 mV) with our internal and external solutions. Work performed in collaboration with Jim Huettner’s laboratory.


Another major focus of our work is to identify transcriptional and epigenetic regulatory controls underlying the development of human cortical interneurons and to understand how their dysregulation contributes to neurodevelopmental disorders. The mammalian cerebral cortex consists of two major types of neurons, excitatory glutamatergic projection neurons that convey information to different regions of the brain and GABAergic interneurons that provide local inhibitory inputs to modulate responses of projection neurons and prevent over-excitation. Imbalances between excitatory and inhibitory neuronal activities can emerge during cortical development. These imbalances often reduce inhibitory signaling through dysfunctional specification, migration, differentiation, or survival of interneurons. Interneuron hypoplasia or dysfunction contributes to many neurological disorders, including epilepsy, schizophrenia, autism spectrum disorder, and intellectual disability syndromes.
We can now model gene regulatory networks that control human cortical interneuron specification and differentiation at a genome-wide level by generating mature interneurons from human pluripotent stem cells (embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs)). We are building gene regulatory networks underlying this process by integrating genome-wide binding profiles of key transcription factors and chromatin regulators, developmental transcriptome and epigenome changes, and effects of manipulating these activities. This work has revealed new regulators of interneuron development, including transcriptional and chromatin modifying activities and non-coding RNAs, enriched in and/or involved in interneuron specification and differentiation.
After transplantation into the neonatal or adult nervous system, cortical interneurons have a striking ability to integrate into neural circuits and to provide inhibitory neuronal function in many locations, including their normal targets in the forebrain (hippocampus, cortex, striatum) as well as upon transplantation into heterologous locations such as the spinal cord. Because of this, transplanted mouse interneurons acquired from the medial ganglionic eminence have shown therapeutic utility in treating disease in mouse models of epilepsy, Parkinson’s disease, chronic pain, schizophrenia and anxiety.  We are currently applying this approach with in vitro differentiated human interneurons, to assess their capacity to engraft and migrate to target locations in the murine brain, and to suppress seizures in a murine model of temporal lobe epilepsy. These approaches can be used to determine how interneuron differentiation or maturation state, or subtype identity, contributes to capacity to engraft, migrate and ameliorate disease phenotypes.
We have also defined genes with interneuron-enriched expression whose mutation contributes to human neurodevelopmental disorders, including inherited epilepsies and autism spectrum disorder. In collaboration with the WUSM Intellectual and Developmental Disability Research Center, we are deriving iPSCs from epilepsy and autism patients with mutations in some of these genes and are performing directed differentiation into cortical excitatory and inhibitory neurons and cerebral organoids. These are subjected to a battery of assays to define developmental, cellular, molecular, and functional abnormalities that contribute to the disorder. We can use these models to assess the relative contributions of genetic background versus pathogenic mutations, by comparisons of isogenic neurons with versus without engineered correction of mutations. We are also using these models to assess how differential expressivity of a disorder among family members carrying a known pathogenic mutation manifests in cellular, molecular, and functional differences between neurons from these family members.


Epigenetic regulation in pediatric glioblastoma.


Dysregulation of the epigenome is also an important but incompletely characterized aspect of tumorigenesis in pediatric glioblastoma (GBM). Malignant gliomas of early childhood frequently carry heterozygous histone H3.3 lysine 27 to methionine (H3K27M) mutations, while those tumors without H3K27M mutations carry mutations in other genes encoding epigenetic regulatory activities that control H3 modification. Polycomb-mediated repressive H3K27 methylation critically controls gene expression and cell state to maintain normal neural and glial stem and progenitor cells and mutation of this histone residue drives pediatric GBM tumorigenesis through incompletely understood mechanisms. Therefore, we are working collaboratively to define epigenetic activities required to maintain the stem cell-like tumor initiating and propagating properties of pediatric and adult GBM versus those involved in maintenance of normal neural and glial stem and progenitor cells. Comparing requirements for epigenetic regulatory activities across these distinct cell contexts will enable us to better understand differences in the biology of tumorigenesis in pediatric versus adult GBM and to identify novel targets for therapeutic intervention.

Research Opportunities


Postdoctoral Fellow


A Postdoctoral Research Associate position is available to study neural development in the laboratory of Kristen L. Kroll at Washington University School of Medicine. Our work involves defining gene regulatory networks and epigenetic regulatory controls that control neural cell fate acquisition, neurogenesis, and the development of specific neuronal cell types, such as cortical interneurons. We are identifying mechanisms by which dysregulation of these processes contributes to neurodevelopmental disorders, including inherited epilepsies, autism spectrum disorder, and neural tube defects. This work uses directed differentiation of human pluripotent stem cells (embryonic stem cells and patient-derived induced pluripotent stem cells), mouse models, and a wide range of cellular, molecular, biochemical, and genomic approaches, to define roles for transcriptional and epigenetic regulation in shaping developmental transitions.


For additional information, see: http://krolllab.wustl.edu/ or http://dbbs.wustl.edu/faculty/Pages/faculty_bio.aspx?SID=4039


Setting/Salary/Benefits:


Our laboratory is in an academic setting in the Department of Developmental Biology at Washington University School of Medicine (St. Louis), an internationally recognized research institution with a dynamic research environment and extensive infrastructural and core facility support. Postdoctoral appointees at Washington University receive a starting salary based on the NIH NRSA guidelines and a generous benefit package. Complete information on the benefit package is located on the WUSM Human Resources Benefits Website (http://medschoolhr.wustl.edu). The St. Louis area combines the attractions of a major city with family-friendly and affordable lifestyle opportunities (http://www.stlouis.com/).


Qualifications:


Candidates should hold a recent PhD with less than 2 years of prior post-doctoral experience. Preference will be given to applicants with a strong interest in and research training relevant to the areas of neural development, stem cell biology, and transcriptional or epigenetic regulation. US citizens are preferred. Interested candidates should send a CV/names of references by email to kkroll@wustl.edu or by regular mail to Kristen L. Kroll, Washington University School of Medicine, Campus Box 8103, 660 S. Euclid Ave, St. Louis, MO 63110.

Selected Publications

 

 

For a complete list of Dr. Kroll's publications, click here

Kristen Kroll, Ph.D.

Associate Professor

Washington University School of Medicine
Campus Box 8103
660 South Euclid Avenue
St. Louis , MO 63110
(314) 362-7045

Links

Other Information

Training

  • 1988 B.A. Northwestern University, Evanston, IL
  • 1994 Ph.D. University of California, Berkeley, California

Academic Positions

  • 1988-94 Dept. of Molecular and Cell Biology
  • University of California at Berkeley
  • 1994-2000 Postdoctoral Fellow with Marc W. Kirschner, Professor and Chair
  • Dept. of Cell Biology, Harvard Medical School, Boston, MA
  • 1998 Independent consultant, Genetics Institute, Cambridge, MA
  • 2000- Assistant Professor, Washington University School of Medicine, Dept. of Molecular Biology and Pharmacology
  • 2007-Associate Professor, Washington University School of Medicine, Dept. of Molecular Biology and Pharmacology

Honors

  • 2007 Hope Award, American Cancer Society, Wash. U. School of Medicine
  • 2006 American Cancer Society Research Scholar, Wash. U. School of Medicine
  • 2000-02 Basil O'Connor Research Award, March of Dimes, Wash. U. School of Medicine
  • 2000-02 Howard Hughes Medical Institute, Faculty Development-Basic Research Award, Wash. U. School of Medicine
  • 1995-98 Postdoctoral Fellowship, Cancer Research Fund of the Damon Runyon-Walter Winchell Foundation, Harvard Medical School
  • 1992 Teaching Effectiveness Award, UC Berkeley
  • 1992 Outstanding Graduate Student Instructor, UC Berkeley 1988 Phi Beta Kappa, Northwestern University
  • 1987 Phi Eta Sigma honorary society member, Northwestern University
  • 1987 National Science Foundation Undergraduate Research Fellowship, Northwestern University
  • 1986-87 Alice G. Hough Scholarship, Northwestern University