Differential gene expression in the mouse hindbrain
In the modern era of biology, molecular studies and sequence analyses have revealed that a wide range of animals have a surprisingly similar collection of conserved genes in their genomes, often referred to as the common “gene toolkit”. These genes encode molecular components that are used to construct the basic body plan shared by many different animals. Therefore, the basis for generating distinct regional properties and tissues within an animal or diversity between species depends to a large degree upon mechanisms that control how and when genes in the common “toolkit” are utilized. This has led to a great deal of interest in understanding the “wiring” or regulatory circuits that control the dynamic and specific patterns of gene expression necessary to form distinct tissues or structures in development and evolution. Understanding these regulatory circuits/networks is also relevant to human health because alterations in their activity are associated with disorders and disease.
The vertebrate central nervous system (CNS) exerts its many activities through the distinct functional roles and properties of different regions, such as the forebrain, midbrain, hindbrain and spinal cord. How do different regions of the CNS form and gain the ability to take on their unique roles? One cellular strategy that contributes to diversity is the process of compartmentation or segmentation. The hindbrain is a complex coordination center for neural activity and segmentation is important for establishing the organizational framework that leads to the formation of complex structures required for hindbrain function. Regional diversity in the hindbrain is achieved through a process of segmentation, whereby neural tissue is transiently divided into seven segmental units, termed rhombomeres. Each rhombomere defines a segregated group of cells that do not mix with their neighbors. This creates a distinct local microenvironment, which allows each segment to adopt a unique set of molecular and cellular properties. For example, rhombomeres play important roles in organizing the cranial nerve network of the medulla oblongata.
Genetic and regulatory analyses in many model systems have demonstrated that the Hox family of transcription factors provide a highly conserved molecular framework or code for specifying distinct regional properties, such as anterior versus posterior, in many tissues. In mouse development, targeted mutations of Hox genes have demonstrated that they are required to regulate multiple aspects of hindbrain segmentation. Using evolutionary comparisons, combined with experimental embryology and transgenic analyses, a large body of evidence indicates that there is a highly conserved gene regulatory network that controls hindbrain segmentation through the Hox homeobox gene family.
The primary goal of my project is to identify and understand rhombomere-specific patterns of gene expression, which are important in generating individual segments and their properties during hindbrain segmentation. Towards this end I am performing transcriptional profiling on whole dissected hindbrains and individual hindbrain segments isolated by laser capture microscopy using any RNA sequencing and a variety of microarray technologies. This analysis is being performed on tissue and segments isolated from different stages during hindbrain development and from wild type and Hox mutant embryos. These studies will contribute to current understanding of the transcriptional programs that govern hindbrain segmentation and the differentiation of rhombomeres.