Human ring chromosomes are abnormal structures formed by intrachromosomal fusions, creating a circular chromosome. Ring chromosome syndrome is a debilitating disorder resulting in severe drug-resistant epilepsy, intellectually disabilities (IQ <70), and developmental delay. Ring chromosome patients and families deal with life-long challenges of prolonged seizures, learning and memory issues, severe psychological disruption, and a feeling of powerlessness, resulting in a great deal of stress and strain. Clinically this disorder affects multiple organ systems including the brain (microcephaly, early onset epilepsy, and intellectual disabilities), the eye, the immune system, and growth. Our laboratory and others, have focused on mapping and characterizing the molecular and cytogenetics of ring chromosome structures; however, to date no published studies have focused on investigating the cellular neuropathology due to lack of appropriate models. To investigate this disorder, we have created a large biobank of cell lines from ring chromosome 14 (r(14)) patients and family members. From these cell lines, we have produced the only model available by generating patient-specific induced pluripotent stem cells, which provide the foundation for studying this devastating disorder that lacks alternative models. In our preliminary work, we find that by differentiating ring chromosome iPSCs toward a forebrain fate we can generate populations of neuronal precursor cells (NPCs) that can be further differentiated into post-mitotic neurons. Neuronal precursor cells harboring the ring chromosome 14 have reduced cellular growth and decreased expression of key telencephalon neuronal markers. Interestingly, a number of genes located on chromosome 14 are involved in neuronal differentiation or maintenance, leading us to postulate that the ring structure modifies expression of this key gene responsible for in vitro cortical cell generation. We have also begun to generate an in vitro cerebral cortex organoid model, which will be important for studying the early embryonic events perturbed in a R(14) developmental model. Mammalian genomes are organized in distinct architectures which allow for the orchestration of proper gene and epigenetic regulation. Our proposed studies will identify ring chromosome 14 orientation in the nucleus, epigenetic marks on chromosome 14, and establish a 3-dimensional (3D) cerebral cortex developmental model for studying phenotypes of Ring chromosome 14 syndrome. We hypothesize that the altered higher order chromosome structure resulting from ring formation disrupts normal chromatin compaction, looping, localization within the nucleus and ultimately gene regulation. The proposed work will provide important tools for studying R(14) syndrome, and yield a comprehensive view of the role a ring chromosome has on DNA positioning, chromatin modifications, and in vitro neuronal development. In addition, this innovative model should provide a strong foundation for future work fully characterizing 3D organoid development in R(14) and provide essential reagents (neuronal tissues) to study the neural circuits and electrophysiological patterns in R(14) patient samples.
Our work aims to develop a neurological model for studying the cellular and molecular abnormalities that are associated with Ring chromosome 14 R(14) clinical phenotypes. We will focus on identifying differences in chromosome positioning in the nucleus, how a circular ring affects DNA-DNA interactions on Chromosome 14, and establishing a reproducible in vitro neuronal developmental model using 3-dimensional ?mini brains?. We anticipate this system will provide a through description of the epigenetic landscape of ring chromosome 14 in neuronal cells, and increase our understanding of how R(14) affects in vitro neuronal development.
