15691-Firulli, Anthony

Anthony B. Firulli, PhD

Carleton Buehl McCulloch Professor of Pediatrics

1044 West Walnut Street
R4 302E

Indianapolis, IN 46202
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In July, 2003, I began working at the Indiana School of Medicine, as an Associate Professor, in the Department of Pediatrics, at the Herman B Wells Center for Pediatric Research. In July, 2009, I was promoted to Professor in the Departments of Pediatrics, Medical and Molecular Genetics, Anatomy & Cell Biology/Biochemistry.

Beginning in January, 2014, I was awarded the title of Carleton Buehl McCulloch Professor of Pediatrics. 

For over 25 years, my independent career focus has been on gaining an understanding of the role that the bHLH Hand/Twist-family of proteins plays during heart development. My group has established that these factors have broad dimerization characteristics and that phosphoregulation of these proteins helps define bHLH partner choice. We have gone on to show that Hand/Twist-family gene dosage within a cell defines a bHLH code, which orchestrates cell specification, differentiation, and morphological patterning. This mechanism is directly involved in causing the human disease. We have discovered that bHLH partner choice pays a key role in the patterning of the face during embryonic development. Hand1 expression within the distal cap of the 1st pharyngeal arch is not necessary for normal craniofacial morphogenesis; however, when HAND1 dimer mutant knock in alleles are activated within the endogenous Hand1 expression domain, there is a pronounced mid face clefting that results from disruption of FGF and SHH signaling resulting in wide spread non-cell autonomous cell death within the forming 1st pharyngeal arch. 

In other studies studies, we have discovered a number of Hand1 transcriptional enhancers that drive tissue specific expression within embryos.  Hand1 transcriptional enhancers necessary and sufficient for recapitulating 1st pharyngeal arch expression, sympathetic nervous system, and left ventricle expression are published. Notable from this work, we show that HAND1 plays important roles in the cardiac conduction system morphogenesis, where Single Nucleotide Polymorphisms (SNPs) within the human HAND1 left ventricle enhancer are associated with abnormal cardiac conduction defects. We show that in gene edited mice which incorporate the human SNPs into the conserved mouse enhancer that transcription factor binding is altered and they present with abnormal cardiac conduction.

Our studies of HAND2 reveal that HAND2 lies downstream of NOTCH signaling within the developing endocardium and its endocardial loss of function results in tricuspid atresia. Single cell transcriptome analysis reveals that the shear stress pathway is impacted in Hand2 endocardial mutants. By looking at HAND2 DNA occupancy peaks within the endocardial genes regulated in our loss-of-function model, we have identified a number of novel endocardial transcriptional enhancers dependent on HAND2 function. 

Our future efforts are focused on the discovery of novel Hand1 and Hand2 regulatory enhancers and identification of downstream targets to reveal the gene regulatory networks that drive embryogenesis. 

Key Publications

Online in PubMed


Titles & Appointments

  • Carleton Buehl McCulloch Professor of Pediatrics
  • Professor of Biochemistry & Molecular Biology
  • Professor of Medical & Molecular Genetics
  • Adjunct Professor of Anatomy, Cell Biology & Physiology
  • Director, Program in Cardiac Developmental Biology
  • Director, University of Ulster Masters Internship Program
  • Education
    1997 FEL Postdoctoral Fellowship, Hamon Center for Basic Cancer Research, University of Texas Southwestern Medical Center, Dallas, TX
    1995 FEL Postdoctoral Fellowship, Department of Biochemistry & Molecular Biology, M.D. Anderson Cancer Center, Houston, TX
    1993 PhD State University of New York at Buffalo
    1987 BS Roger Williams College
  • Research

    The biological question that holds my research interest is gaining an understanding of the transcriptional mechanisms that control the cell specification and differentiation of multi-potential cells. When I was a graduate student, the myogenic basic loop-helix (bHLH) transcription factors were identified and shown to program fibroblast cell lines such as 10T1/2 to the skeletal muscle lineage. The finding that a single family of transcription factors could define cell identity led me to look for novel transcription factors that played similar roles in the specification of tissues such as the heart. These efforts resulted in my study of the Twist class of bHLH factors Hand1, Hand2, and Twist1. Unlike the myogenic bHLH transcription factors, Twist-family bHLH factors are expressed in a wide range of tissues including heart, cardiac neural crest, lateral mesoderm, the developing sympathetic nervous system and other mesenchymal cell populations during development as well as in pathologies such as cancer. In our study of the biological properties of Twist-family proteins, we discovered that unlike the myogenic bHLH factors, these bHLH factors exhibit promiscuous dimerization characteristics such that Hand1, Hand2 and Twist1 can form homo and hetero dimers in addition to heterodimers with E-proteins. This expanded dimerization profile sets up a model whereby changes in the biological function of these factors is dependent on the various bHLH proteins expressed within a given cell and the mechanisms that dictate dimer partner choice. If in fact Twist-family biological function is regulated by dimer partner choice then an obvious question: How is dimer choice regulated? Must be asked. Our first insights into the mechanisms that control Twist-family dimerization choices came from our discovery of a phosphoregulatory circuit composed of the kinases PKC and PKA and the trimeric phosphatase, PP2A, containing the B56d regulatory subunit. These enzymes modulate the phosphorylation state of Hand and Twist proteins on 2 evolutionarily conserved residues within Helix I of the bHLH domain. Florescence Resonance Energy Transfer (FRET) and in vivo expression analysis show that phosphorylation of Hand1, Hand2 and Twist1 on these conserved residues modulates dimer partner choice, and in the case of Twist1, human mutations that hobble normal phosphoregulation result in the autosomal dominant human disease Saethre Chotzen Syndrome (SCS; OMIM 101400.) Furthermore, loss of normal Twist1 phosphorylation in SCS effects Twist1's ability to antagonize the functions of Hand2 and that by reducing the gene dosage of Hand2 one can rescue the SCS phenotypes in the Twist1 haploinsufficient mouse model validating the hypothesis that Twist-family dimer choice is critical for normal development to proceed. To pursue our research goals we employ both conditional gain-of-function and loss-of-function mouse models, standard molecular and biochemical techniques as well as transcriptional analysis using in vivo and in vitro systems. We have gone on to show that dimer regulation affects craniofacial morphogenesis, that Twist1 is a master repressor or the neuronal program and have identified the regulatory control domains of Hand1. Our future efforts will further characterize the posttranslational modifications within Twist family of proteins and to explore how phosphoregulation and partner choice drive tissue-specific development programs using gene targeted mouse models that allow for the conditional activation of mutant protein expression in the wide spectrum of mesenchymal tissues that require Twist-class bHLH factors for proper development. By using large sequence data that has revealed mutations of Hand and Twist proteins found in human patients presenting with disease, we will model these mutations in vivo and deduce their contributions to congenital defects that account for 1% of all live births.

  • Professional Organizations
    Ad Hoc Reviewer: NIH/NHLBI, NIH NCF/NIGMS, NIH/NHLBI Mentored Clinical Scientist Career Development Awards
    American Chemical Society: High Achievement in Chemistry Award
    American Heart Association
    American Heart Association: Established Investigator
    American Society for Biochemistry and Molecular Biology
    Editorial Boards: Developmental Biology Journal, Journal of Biological Chemistry, AIMS Genetics, Scientific Reports
    Member: NIH CDD/NHLBI
    Muscular Dystrophy Association: William C. Gibson Neuromuscular Disease Research Fellowship (1993-1996)
    Society for Developmental Biology
    Society for Neuroscience
    Society for Pediatric Research
    Special Review Panels: National Science Foundation, Wellcome Trust
  • Awards
    Org: Indiana University
    Desc: Glenn W. Irwin, Jr., M.D., Research Scholar Award
    Scope: University
    Org: American Heart Association
    Desc: American Heart Association, Established Investigator Award
    Scope: National
    Org: Muscular Dystrophy Association
    Desc: William C. Gibson Neuromuscular Disease Research Fellowship
    Scope: National
    Org: Roger Williams University
    Desc: Alpha Chi Edward L. Davis Award
    Scope: University
    Org: American Chemical Society
    Desc: High Achievement in Chemistry Award
    Scope: University
    Org: Who's Who Among Students in American Universities and Colleges
    Desc: Who's Who Among Students in American Universities and Colleges
    Scope: National

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