Dr. Roy Sillitoe

The ultimate goal of our work is to uncover the developmental origins of behaviors that are controlled by the cerebellum. The cerebellum participates in a number of functions including motor coordination, learning, balance, and possibly even cognition. During normal behavior the cerebellum integrates these functions into highly refined responses. It has been suggested that the circuitry responsible for such complex internal processing is exquisitely organized. Indeed the cerebellum is parcellated into a complex map of functional microzones that correspond to an underlying array of parasagittal stripes of gene expression (e.g. ZebrinII (green) and Plc b 4 (red) in the top figure). Given that the patterns of ZebrinII and other markers are remarkably reproducible from animal to animal, stripes of gene expression are potential targets for experimentally manipulating the circuitry of the cerebellum in a controlled manner. Our lab is taking a systematic genetic approach to manipulating individual stripe patterns with the goal of teasing apart the functional architecture and behavioral capabilities of the developing cerebellum. We are fortunate in that several behaviors that are dependent on cerebellar function have been extensively studied, and the circuits underlying these behaviors have been elucidated. However, we have only limited knowledge about how these circuits are constructed. Our aim is to elucidate the molecular mechanisms responsible for transforming embryonic connections into functional adult circuits. The internal micro-circuitry within the cerebellum appears to undergo extensive remodeling before the adult map is attained. We previously showed that the homeobox containing genes Engrailed 1 and 2 (En1/2) are required for patterning Purkinje cell parasagittal stripes within functionally distinct anterior-posterior domains (Sillitoe et al., 2008a). Our current aim is to investigate whether En1/2 are also required for patterning the topographic connections within parasagittal mircrozone/gene expression stripes. We are using sophisticated mouse genetic techniques in combination with immunohistochemistry, in situ hybridization, genetic tract tracing (e.g. eGFP), and traditional methods of neuroanatomical tract tracing (e.g. WGA-HRP labeled mossy fibers in the bottom figure) to determine how developing circuits are sculpted into adult topography maps. Given that En1 and En2 have dominant functions in patterning functionally distinct regions of the cerebellum (Sillitoe et al., 2008a), we expect that manipulating each En gene alone or both genes together will cause specific defects in the cerebellar micro-circuitry and ultimately result in distinct behavioral outcomes. In collaboration with Drs. Kamran Khodakhah and Maria Gulinello we are using electrophysiology and a panel of behavioral paradigms to determine whether particular developing circuits are altered in En1/2 mice, and whether these alterations underlie specific behavioral abnormalities. Consistent pathological defects are found in the cerebellum of children with Autism Spectrum Disorder (ASD). Importantly, human ENGRAILED2 is thought to be a susceptibility locus for ASD, and En2 null mice have behavioral deficits suggestive of autism-like phenotypes. By using state-of-the-art genetic approaches we aim to better understand how circuit complexity is built into the nervous system. Our hope is that by pairing molecular genetics with other functional approaches we will shed light on the embryonic origins of behaviors that are altered in developmental neurological diseases such as ASD.

Selected Publications