Rolf W. Stottmann, Ph.D. - US grants

DESCRIPTION (provided by applicant): Congenital malformations involving the neural tube are among the most common birth defects worldwide. The mouse has become an excellent system to study these malformations due to the similarities to human development and the genetics available to study developmental processes in the mouse. Several lines of evidence implicate Bone Morphogenetic Proteins (BMPs) in neurulation. BMP activity (particularly that of the BMP 2/4 signaling pathway) is implicated in forming the neural plate and neural crest as well as patterning the neural tube (formed from the neural plate) along the dorsal-ventral axis, particularly with respect to neuronal progenitors. BMP signaling has been difficult study in the mouse, however, as many null mutations are lethal before the process of neurulation. We aim to address the role of BMPs in dorsal neural tube development using two different approaches. The BMP antagonism gene, Noggin, is expressed in the neural tube and loss of function in the mouse results in severe neural tube defects resembling human malformations. We will further study the role of noggin in development and patterning of the neural tube to understand the basis of these defects. To address BMP signaling, we will use the Cre-Lox tissue specific recombination system to inhibit BMP signal transduction in the dorsal neural tube. We hypothesize this will result in severe defects in neurulation, patterning and/or neural crest induction, uncovering the specific contributions of BMP2/4 signaling to neural tube elaboration.

[unreadable] DESCRIPTION (provided by applicant): The human forebrain is the organ responsible for many of our uniquely human qualities, including reasoning, emotion and memory. This complex organ can be afflicted by a wide array of diseases from developmental abnormalities with lifelong consequences to later onset diseases such as neurodegeneration, or tumorigenesis. Despite this importance, there is much to learn about the molecular control of brain development. One approach to gain further understanding of the brain is to uncover more of the genetic components involved in its development, function and disease. The mouse, especially with its unique genetic tools, serves as an excellent model for human physiology and recent advances in genomic technologies allow us to apply large scale genetic approaches to studies of the brain. This proposal will use mouse genetic tools in a mutagenesis experiment to identify and begin to characterize novel genes required for normal development and function of the mouse brain. ENU mutagenesis in the mouse is an established tool to create autosomal recessive mutations, similar to those found in the human population, which can then be mapped and cloned. The aims of the proposal are to (1) screen for ENU- induced mutations in the mouse which affect brain development, and (2) begin to characterize two of the mutations already identified in preliminary studies. The identification of new alleles required for brain development is likely to contribute to our current state of understanding of the brain's development and function. Recent advances in our understanding of human disease have demonstrated the significant connection between individual genetic makeup and causation of, or predisposition to, specific diseases. One way to further study the roots of human disease is the use of similar experimental animal models to discover new genes related to specific disorders. By identifying more of the underlying causes of disease, the function of these genes can be elucidated, leading to increased treatments for the ultimate treatment and resolution of human disorders. This proposal is designed to uncover some of the fundamental mechanisms in brain development and disease. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): The mammalian neocortex is an enormous network of cells, each making thousands of connections and an array of neurological conditions can result from inappropriate cortical structure or connectivity. Many of these congenital brain defects have a genetic origin but we still lack a full understanding of the genes and mechanisms involved. The overall objective of this application is to use forward genetic approaches in mouse and human to identify and validate novel alleles important for development of cortical circuitry and overall structure. Our central hypothesis is that a synergistic and unbiased forward genetic approach in mouse and human will lead to fundamental discoveries in the genetics of cortical circuit formation and structural development. The rationale of this proposed research is that by identifying novel genes through forward genetic approaches which are required for normal cortical development using both human and mouse genetics, we are then positioned to use this information and tools to study the etiological mechanisms of human cortical malformations in subsequent studies. We will test this central hypothesis and accomplish the goals of this application by pursuing the following three specific aims: 1) use forward genetics in the mouse to efficiently generate and capture genetic mutations in loci important for cortical circuit formation and structural development, 2) identify and validate causal mutations in novel mouse models of cortical circuit formation and structural brain defects, and 3) apply next-generation sequencing approaches to identify mutations leading to human movement disorders and structural brain defects. The aims are accomplished by an ENU mutagenesis approach in the mouse with the addition of a novel transgenic reporter which is expressed specifically in cortical layer V pyramidal neurons. The mutations are then cloned and validated through a number of functional studies. The human genetics studies are performed with the application of exome sequencing to carefully selected familial cases of movement disorders and structural brain malformations. These studies will identify several genes essential for mammalian forebrain structure and function. The significance of this work is found in the specific application to cortial circuitry and structure, and that an unbiased approach such as this has the capability to implicate entirely new pathways in neurological disease. A synergistic approach using both mouse and human genetics to specifically query these aspects of neural development allows fundamental insights into the genetics of development and disease. Such knowledge is not only critical to further understand the basic mechanisms of neurodevelopment, but also has immediate clinical relevance through identification of a number of potential therapeutic targets. Furthermore, these mouse models provide a reusable resource to directly characterize the role of the mutated gene in neurodevelopment, and potentially serve as a tool to test future therapeutic interventions. Taken together, these findings are therefore applicable to basic developmental neurobiology, pediatric and adult neurology, human genetics and genetic counseling.

DESCRIPTION (provided by applicant): Ciliopathies are a spectrum of diseases resulting from defects in primary cilia function affecting 1:800 people. Primary cilia are microtubule based organelles found on almost all cells and crucial for proper signal transduction of a number of molecular pathways. Ciliopathies affect a wide range of tissues including the nervous system, craniofacial tissues, skeleton, kidneys, lungs and digestive organs. These manifest as both congenital and adult-onset defects. Genetic studies of ciliopathy patients show TTC21B (tetratricopeptide repeat domain-containing protein1B) is the most commonly mutated cilia gene identified to date. In addition to defects associated with loss of just TTC21B, mutations in trans with a number of other ciliary genes lead to ciliopathies. We have recently shown loss of Ttc21b in the mouse leads to perinatal lethality and organogenesis defects. We also note some of these phenotypes are dependent on the specific inbred mouse strain background. The TTC21B protein is large with many protein-protein interaction domains and important for intraflagellar transport and regulating signal transduction in the cilium. All of these data together lead us to the central hypothesis that TTC21B serves as a network hub for scaffolding and trafficking activities essential for proper cilia form and function. The goal of this application is identify genes and proteins interacting with Ttc21b: the Ttc21b interactome, and begin to understand how these interact in the cell. The rationale for the project is that a more complete understanding of how TTC21B acts is likely to give insight to a range of ciliopathies. We will address this hypothesis and achieve these goals with the following three specific aims: 1) identify chromosomal regions containing genes modifying the Ttc21bnull/null phenotype in the B6 and FVB mouse strains, 2) identify novel genetic interactions with Ttc21b using a forward genetic approach, and 3) study functional mechanisms of genes interacting with Ttc21b. The first aim will utilize a QTL analysis to identify loci regulating the strain specific phenotypes we see in Ttc21bnull/null embryos. The second aim will take a forward genetic, ENU mutagenesis approach to identify novel interactions with TTC21B in an unbiased manner. The third aim will recapitulate interactions identified in humans or previously identified in mouse. After verifying these interactions yield ciliopathy phenotype(s), we will perform further analyses in vitro and in vivo to study the molecular mechanisms of ciliary dysfunction. These studies will focus on ciliary trafficking and Shh signal transduction. The significance of this project is that these studies wil together dramatically increase our understanding of how TTC21B acts within the primary cilium and why perturbation of function leads to ciliopathic disease. These studies will fill an important gap in our knowledge and identify possible areas for therapeutic intervention. These advances are not specific to TTC21B but are likely going to be largely applicable to multiple areas of primary cilia biology inter- est. The innovation of this project lies in the application of unbiase genetic techniques to identify the Ttc21b interactome in close concert with solid molecular studies to determine the underlying mechanism(s).

Genetic defects in the cholesterol bio-synthesis pathway lead to a spectrum of human dysmorphology syndromes with a key common theme of altered craniofacial, skeletal and central nervous system (CNS) development. A deep mechanistic understanding of how these malformations arise will require a multi- disciplinary approach. As part of this R03 to ?establish basic science-clinical collaborations to understand structural birth defects,? we will merge the expertise of three teams at the interface of genetics, embryology and sterol metabolism. We will combine clinical acumen and biochemical expertise with molecular embryology to synergistically approach the question of how sterol metabolism defects lead to brain and craniofacial birth defects. We will focus specifically on three enzymes in the post-squalene portion of the cholesterol biosynthesis pathway: hydroxysteroid (17-beta) dehydrogenase 7 (Hsd17b7), 24-dehydrocholesterol reductase (Dhcr24) and 7-dehydrocholesterol reductase (Dhcr7). These are neighboring enzymes in the latter portion of the pathway, but have very different phenotypes when ablated. The rationale for this proposal is that the molecular basis for these structural birth defects in mouse and humans has not been fully elucidated. Furthermore, detailed analysis of the mouse CNS phenotypes after birth has been prevented by perinatal death of the null mutants. Our central hypothesis is that the differing phenotypes within the spectrum of cholesterol metabolism errors occur because defects at different steps of the pathway lead to the accumulation of different sterol intermediates and/or altered lipid raft composition, which then affect embryonic development differently. We have collected and generated 5 mouse alleles (Hsd17b7rudolph, Dhcr24null, Dhcr7null, Dhcr24flox, Dhcr7flox and) to specifically address this hypothesis in this exploratory proposal. In addition, we propose to generate new tools to further develop our overarching hypothesis. We propose to address this hypothesis with two specific aims: (1). Analysis of sterols and lipid rafts in developing brains and faces upon loss of Hsd17b7, Dhcr24, and Dhcr7. (2). Determine the consequences for loss of cholesterol biosynthesis genes Hsd17b7, Dhcr24, and Dhcr7 in the cortex. The experiments in this proposal will accomplish two goals: (1) We will substantially increase our understanding of the effects of loss of three crucial cholesterol biosynthesis enzymes on CNS development. These preliminary studies and the novel Hsd17b7 allele will position us to address even more mechanistic hypotheses about the role of these enzymes, and sterol metabolism more broadly, in congenital structural brain defects, (2) We will establish an effective and demonstrable collaboration between an embryologist, a clinician researcher and an expert in sterol analysis with a shared interest in the role of sterol metabolism in structural birth defects. !

Craniofacial anomalies are among the most common congenital birth defects (>1 in 700 live births) with a large, but poorly understood, genetic component. The overall objective of this application is to take a human genetic approach to identify the genetic causes of congenital craniofacial malformations with complementary animal model studies. Our central hypothesis is that careful selection (based on pedigree analysis, phenotypic presentation, etc.) and genomic sequencing of pedigrees will allow us to identify novel causes of craniofacial malformations and facilitate experiments to uncover the underlying mechanisms. The rationale of this proposed research is that identification of variants causing craniofacial malformations will improve our understanding of the underlying pathogenic mechanisms, inform patient counseling, and ultimately lead to improved diagnosis, treatment, and patient care. We plan to test this central hypothesis and accomplish the goals of this application by pursuing the following specific aims: 1) use whole genome sequencing to identify variants leading to human syndromic cleft lip and palate, 2) determine the mechanism of Fzd2 truncation pathogenesis in skeletal development, and 3) perform functional analysis of candidate variants in novel human craniofacial malformations. Aim 1 will be accomplished by whole genome sequencing of selected patients from our CCHMC cohort. In Aim 2, we will further study a novel mouse model of FZD2 omodysplasia to evaluate the role on non-canonical Wnt signaling in this disorder. In Aim 3, we will apply our expertise in creation and study of mouse models to understand the molecular mechanism of variants identified in affected human probands. The results from this proposal will further identify genes essential for human craniofacial development and have direct and persistent relevance for craniofacial developmental biology, human genetics and genetic counseling. By identifying novel roles for single genes, entire gene regulatory networks can often be implicated which can dramatically increase the range of potential therapeutic targets. Moreover, the novel animal models generated as part of these studies can be further utilized as tools for understanding basic mechanism(s) of disease and potentially as platforms for testing therapeutic interventions in future studies. For clinicians, increased understanding of the specific genes involved in craniofacial development and connectivity leads to more effective diagnosis, treatment, risk-assessment, and family planning.

The goal of the research in my laboratory is to study the genetic basis of human craniofacial and CNS malformations. Our efforts in both human and mouse genetics over the past several years have continually directed us towards the primary cilium as a critical hub in signaling for human health and disease. Ciliopathies are diseases associated with both severe congenital malformations as well as nonlethal craniofacial dysmorphology, intellectual disability and obesity (among other conditions). It is clear from the literature that modifying loci are crucial components in understanding much of human disease, but is especially true of the ciliopathies. The focus of this proposal is largely on the primary cilia gene tetratricopeptide repeat domain 21B (Ttc21b). Ttc21b homozygous mouse mutants have several striking features on their own but our preliminary data and the work of others clearly show that TTC21B is a hub in a human ciliopathy network. We have taken four of these candidate interactions from human genetics and recreated them in mouse. All four genes interact with Ttc21b but the cellular and mechanisms of the resulting phenotypes are not yet elucidated. We have also identified multiple novel interacting loci with a combination of ENU mutagenesis and a QTL analysis of the genetic background effects on the severity of the microcephaly phenotype. Thus, we have significant experience in the field and have identified four crucial gaps in knowledge we will address with the support of this MIRA award: 1) How does Ttc21b have such tissue specific effects on organ physiology and developmental signaling, 2) What are the genetic interactors and modifiers of Ttc21b which alter these ciliopathy phenotypes, 3) what is the cellular function of Ttc21b inside the primary cilium, 4) what is the role of Ttc21b outside the cilium. We will use a combination of genetics, molecular embryology, cell biology and biochemistry to address these topics. Many of the ciliary genes are identified to have roles within the primary cilium, but any function outside the cilium has not been elucidated. Identification of such roles would have very a significant effect on the field. Our favorite hypothesis based on preliminary data is that Ttc21b has significant roles in neuronal trafficking. It is clear that a better understanding of human disease will require knowledge of modifying loci and the underlying mechanism(s). Ttc21b is ripe for exploration as a crucial component in a ciliopathy genetic network. A combination of mouse embryology and cell biology inspired by human genomics is an ideal entry point. Our work is likely to not only contribute to knowledge about ciliopathies but point the way forward as a general experimental paradigm for a number of different pathophysiological contexts.