Susan Dymecki | |
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Born | Philadelphia, Pennsylvania, U.S. | 19 June 1960
Alma mater | University of Pennsylvania, Johns Hopkins University School of Medicine |
Known for | Flp-FRT genetic recombination tools, mapping serotonergic heterogeneity and function |
Awards | Rita Allen Foundation Scholar, Gulf Oil Outstanding Achievement in Biomedical Science Award, AAAS Member |
Scientific career | |
Fields | Neuroscience, genetics |
Institutions | Harvard Medical School |
Susan M. Dymecki (born June 19, 1960) is an American geneticist and neuroscientist and director of the Biological and Biomedical Sciences PhD Program at Harvard University. [1] Dymecki is also a professor in the Department of Genetics and the principal investigator of the Dymecki Lab at Harvard. Her lab characterizes the development and function of unique populations of serotonergic neurons in the mouse brain. To enable this functional dissection, Dymecki has pioneered several transgenic tools for probing neural circuit development and function. Dymecki also competed internationally as an ice dancer, placing 7th in the 1980 U.S. Figure Skating Championships. [2] [3] [4]
Dymecki was born in Philadelphia, Pennsylvania, on June 19, 1960. [5] Before becoming a scientist, Dymecki was a competitive ice dancer. [3] She started ice dancing when she was 13 years old and competed at the national level within the United States during high school. [3]
Dymecki pursued a Bachelor of Science in Engineering at the University of Pennsylvania, and during this time she competed internationally in ice dancing. [3] When Dymecki was 20 years old, her and her ice dancing partner ranked 6th in the United States. [5] After taking a year off to compete, she completed her bachelor's degree and then stayed at UPenn to complete a Master of Science in Engineering. [1] During her Master's, she worked in the lab of Carl Theodore Brighton exploring the use of electric current in stimulating osteogenesis. [6]
After completing her master's degree, she pursued her MD-PhD in 1985 at the Johns Hopkins School of Medicine, studying under Stephen Desiderio. [7] During her PhD, Dymecki discovered a new gene expressed in B cells, called blk for B Lymphoid Kinase, which helps to initiate an immune response. [5] After completing her MD-PhD training in 1992, Dymecki became a Helen Hay Whitney Fellow and John Merck Scholar at the Carnegie Institution for Science in the Department of Embryology in Washington, DC. [8] While completing her postdoctoral training, she pioneered novel genetic tools with which to study development in the mammalian nervous system. [8] In 1997, Dymecki filed a patent for her genetic tool, which consisted of DNA constructs that enable transgenic expression of FRT recombination sites and a Flp recombinase in non-human mammals. [9] Her technology has aided many researchers in achieving gene insertion, deletion, and modulation as well as label cell lineages to explore developmental stages. [9]
During graduate school, Dymecki isolated and characterized a novel gene, blk, named after B Lymphoid Kinase. [10] This gene encodes a tyrosine kinase protein, and is specifically expressed in B cell lineages. [10] Through further characterization of the transcriptional of blk, Dymecki found that none of its transcriptional start sites are preceded by TATA elements, AT-rich elements, or other common start site motifs. [11] Dymecki also found that blk is expressed in pro-, pre-, and mature B cells, but not the antibody producing plasma cells. [11]
During Dymecki's postdoctoral work at the Carnegie Institute, she pioneered the development of novel vectors that enabled targeted genetic manipulation of specific populations of mammalian cells. [12] Using Flp recombinase, Dymecki shows that her genetic constructs can be expressed in mammalian cells to activate specific genes. [12] In a following paper in 1996, Dymecki showed that her tool not only worked in cell culture, but also in vivo in living transgenic mice to mediate gene insertion and deletion via recombination at FRT sites. [13] Dymecki's paper was the inaugural paper to show that Flp technology could be used to make specific alterations to the mouse genome. [13]
In 1998, Dymecki joined the faculty at Harvard Medical School and became an associate professor in the Department of Genetics. [3] Dymecki's involvement with graduate education led her to become the associate director of the Biological and Biomedical Sciences PhD program in 2004. [1] By 2010, Dymecki was promoted to Full Professor in the Department of Genetics, and the following year she became the Director of the Biological and Biomedical Science PhD Program at Harvard. [14]
As the Principal Investigator of the Dymecki Lab, Dymecki runs a research program dedicated to exploring the development and function of serotonin neurons in the rodent brain. [1] Since Dymecki has found that serotonergic neurons are implicated in a wide range of critical processes from respiration, to thermal regulation, to emotional state, her research addresses fundamental questions about how the specific neural subtypes and circuits underlying these processes develop such that they can be targeted in the future to treat disease. [1]
After establishing Flp recombinase as an available genetic tool for site specific recombination in the mouse brain, Dymecki further optimized this tool. [15] By creating the FLPe deleter strain, which uses an enhanced, thermostable version of Flp, Dymecki found that her tool was just as effective as the already established Cre-loxP tools. [15] Since highly specific targeting of cell populations requires combinatorial genetic strategies, Dymecki's optimization enabled Flp and Cre to be used together in mammalian transgenic systems to perform highly targeted mutations. [15] Following this optimization, Dymecki and her team created a FLPer (“flipper”) mouse line that has global, constitutive Flp expression that can be used to label specific cell populations, or to be crossed with other strains to create opportunities for cell-type specific conditional knockouts. [16]
Dymecki's lab uses their transgenic tools to probe the diversity of serotonin neurons in the central nervous system. [17] Using a variety of genetic profiling and developmental mapping techniques, Dymecki and her team were able to identify various subpopulations of serotonin neurons within the brainstem, and show the immense transcriptional diversity both between and within anatomically defined subpopulations of serotonin neurons. [17] They also found that these transcriptional, anatomical, and molecular differences, lead to differences in function. [17]
Narrowing in on specific subtypes of serotonin neurons has enabled Dymecki and her team to identify the unique behaviors modulated by specific populations of serotonin neurons. For example, the Pet1+ serotonin neurons that also express either dopamine receptor 1 or dopamine receptor 2 were shown to be implicated in aggression. [18] When these neural subtypes were silenced, male aggressive behavior in mice was increased, suggesting the unique role played in a behavior by a very specific population of brainstem serotonergic neurons. [18] Dymecki and her colleagues then found that serotonergic neurons also mediate aggression in Drosophila. [19] They found two serotonergic projections, a GABAergic projection that decreased aggression when stimulated, and a cholinergic projection that increased aggression when stimulated. [19]
Dymecki and her team have characterized the role of serotonin neurons in the regulation of breathing dynamics. [20] By chemogenetically manipulating single sub-populations of serotonin neurons, they found one population, expressing Egr1-Pet1 that increases ventilation in response to acidosis. [20] Following this study, Dymecki and her colleagues identified another unique serotonin population, this time characterized by Tac1-Pet1 that are also implicated in driving ventilation but differ in their projection targets and methods of sensing inhaled CO2. [21]
Serotonin or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex, touching on diverse functions including mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vasoconstriction.
Gene knockouts are a widely used genetic engineering technique that involves the targeted removal or inactivation of a specific gene within an organism's genome. This can be done through a variety of methods, including homologous recombination, CRISPR-Cas9, and TALENs.
Mosaicism or genetic mosaicism is a condition in which a multicellular organism possesses more than one genetic line as the result of genetic mutation. This means that various genetic lines resulted from a single fertilized egg. Mosaicism is one of several possible causes of chimerism, wherein a single organism is composed of cells with more than one distinct genotype.
A transgene is a gene that has been transferred naturally, or by any of a number of genetic engineering techniques, from one organism to another. The introduction of a transgene, in a process known as transgenesis, has the potential to change the phenotype of an organism. Transgene describes a segment of DNA containing a gene sequence that has been isolated from one organism and is introduced into a different organism. This non-native segment of DNA may either retain the ability to produce RNA or protein in the transgenic organism or alter the normal function of the transgenic organism's genetic code. In general, the DNA is incorporated into the organism's germ line. For example, in higher vertebrates this can be accomplished by injecting the foreign DNA into the nucleus of a fertilized ovum. This technique is routinely used to introduce human disease genes or other genes of interest into strains of laboratory mice to study the function or pathology involved with that particular gene.
Cre-Lox recombination is a site-specific recombinase technology, used to carry out deletions, insertions, translocations and inversions at specific sites in the DNA of cells. It allows the DNA modification to be targeted to a specific cell type or be triggered by a specific external stimulus. It is implemented both in eukaryotic and prokaryotic systems. The Cre-lox recombination system has been particularly useful to help neuroscientists to study the brain in which complex cell types and neural circuits come together to generate cognition and behaviors. NIH Blueprint for Neuroscience Research has created several hundreds of Cre driver mouse lines which are currently used by the worldwide neuroscience community.
Site-specific recombinase technologies are genome engineering tools that depend on recombinase enzymes to replace targeted sections of DNA.
Cre recombinase is a tyrosine recombinase enzyme derived from the P1 bacteriophage. The enzyme uses a topoisomerase I-like mechanism to carry out site specific recombination events. The enzyme is a member of the integrase family of site specific recombinase and it is known to catalyse the site specific recombination event between two DNA recognition sites. This 34 base pair (bp) loxP recognition site consists of two 13 bp palindromic sequences which flank an 8bp spacer region. The products of Cre-mediated recombination at loxP sites are dependent upon the location and relative orientation of the loxP sites. Two separate DNA species both containing loxP sites can undergo fusion as the result of Cre mediated recombination. DNA sequences found between two loxP sites are said to be "floxed". In this case the products of Cre mediated recombination depends upon the orientation of the loxP sites. DNA found between two loxP sites oriented in the same direction will be excised as a circular loop of DNA whilst intervening DNA between two loxP sites that are opposingly orientated will be inverted. The enzyme requires no additional cofactors or accessory proteins for its function.
Recombinases are genetic recombination enzymes.
In genetics, Flp-FRT recombination is a site-directed recombination technology, increasingly used to manipulate an organism's DNA under controlled conditions in vivo. It is analogous to Cre-lox recombination but involves the recombination of sequences between short flippase recognition target (FRT) sites by the recombinase flippase (Flp) derived from the 2 µ plasmid of baker's yeast Saccharomyces cerevisiae.
Recombination activating gene 2protein is a lymphocyte-specific protein encoded by RAG2 gene on human chromosome 11. Together with RAG1 protein, RAG2 forms a V(D)J recombinase, a protein complex required for the process of V(D)J recombination during which the variable regions of immunoglobulin and T cell receptor genes are assembled in developing B and T lymphocytes. Therefore, RAG2 is essential for generation of mature B and T lymphocytes.
Site-specific recombination, also known as conservative site-specific recombination, is a type of genetic recombination in which DNA strand exchange takes place between segments possessing at least a certain degree of sequence homology. Enzymes known as site-specific recombinases (SSRs) perform rearrangements of DNA segments by recognizing and binding to short, specific DNA sequences (sites), at which they cleave the DNA backbone, exchange the two DNA helices involved, and rejoin the DNA strands. In some cases the presence of a recombinase enzyme and the recombination sites is sufficient for the reaction to proceed; in other systems a number of accessory proteins and/or accessory sites are required. Many different genome modification strategies, among these recombinase-mediated cassette exchange (RMCE), an advanced approach for the targeted introduction of transcription units into predetermined genomic loci, rely on SSRs.
Conditional gene knockout is a technique used to eliminate a specific gene in a certain tissue, such as the liver. This technique is useful to study the role of individual genes in living organisms. It differs from traditional gene knockout because it targets specific genes at specific times rather than being deleted from beginning of life. Using the conditional gene knockout technique eliminates many of the side effects from traditional gene knockout. In traditional gene knockout, embryonic death from a gene mutation can occur, and this prevents scientists from studying the gene in adults. Some tissues cannot be studied properly in isolation, so the gene must be inactive in a certain tissue while remaining active in others. With this technology, scientists are able to knockout genes at a specific stage in development and study how the knockout of a gene in one tissue affects the same gene in other tissues.
RMCE is a procedure in reverse genetics allowing the systematic, repeated modification of higher eukaryotic genomes by targeted integration, based on the features of site-specific recombination processes (SSRs). For RMCE, this is achieved by the clean exchange of a preexisting gene cassette for an analogous cassette carrying the "gene of interest" (GOI).
Brainbow is a process by which individual neurons in the brain can be distinguished from neighboring neurons using fluorescent proteins. By randomly expressing different ratios of red, green, and blue derivatives of green fluorescent protein in individual neurons, it is possible to flag each neuron with a distinctive color. This process has been a major contribution to the field of neural connectomics.
Tyrosine-protein kinase BLK, also known as B lymphocyte kinase, is a non-receptor tyrosine kinase that in humans is encoded by the BLK gene. It is of the Src family of tyrosine kinases.
In molecular cloning and biology, a gene knock-in refers to a genetic engineering method that involves the one-for-one substitution of DNA sequence information in a genetic locus or the insertion of sequence information not found within the locus. Typically, this is done in mice since the technology for this process is more refined and there is a high degree of shared sequence complexity between mice and humans. The difference between knock-in technology and traditional transgenic techniques is that a knock-in involves a gene inserted into a specific locus, and is thus a "targeted" insertion. It is the opposite of gene knockout.
In genetics, floxing refers to the sandwiching of a DNA sequence between two lox P sites. The terms are constructed upon the phrase "flanking/flanked by LoxP". Recombination between LoxP sites is catalysed by Cre recombinase. Floxing a gene allows it to be deleted, translocated or inverted in a process called Cre-Lox recombination. The floxing of genes is essential in the development of scientific model systems as it allows researchers to have spatial and temporal alteration of gene expression. Moreover, animals such as mice can be used as models to study human disease. Therefore, Cre-lox system can be used in mice to manipulate gene expression in order to study human diseases and drug development. For example, using the Cre-lox system, researchers can study oncogenes and tumor suppressor genes and their role in development and progression of cancer in mice models.
Norbert Perrimon is a French geneticist and developmental biologist. He is the James Stillman Professor of Developmental Biology in the Department of Genetics at Harvard Medical School, an Investigator at the Howard Hughes Medical Institute, and an Associate of the Broad Institute. He is known for developing a number of techniques for used in genetic research with Drosophila melanogaster, as well as specific substantive contributions to signal transduction, developmental biology and physiology.
Cell lineage denotes the developmental history of a tissue or organ from the fertilized embryo. This is based on the tracking of an organism's cellular ancestry due to the cell divisions and relocation as time progresses, this starts with the originator cells and finishing with a mature cell that can no longer divide.
Genome editing of synthetic target arrays for lineage tracing (GESTALT) is a method used to determine the developmental lineages of cells in multicellular systems. GESTALT involves introducing a small DNA barcode that contains regularly spaced CRISPR/Cas9 target sites into the genomes of progenitor cells. Alongside the barcode, Cas9 and sgRNA are introduced into the cells. Mutations in the barcode accumulate during the course of cell divisions and the unique combination of mutations in a cell's barcode can be determined by DNA or RNA sequencing to link it to a developmental lineage.