Developmentally regulated expression of Thy-1 in structures of the mouse sensory-motor system

Thy-1 is a cell-surface molecule of the immunoglobulin superfamily which is expressed at high levels in the mature nervous system. Thy-1 has been implicated in regulating axonal outgrowth and synaptic function, but little is known regarding its cellular localization and expression in the central nervous system (CNS) during development or in adulthood. In this study, Thy-1 gene expression and protein localization were examined in sensory-motor and related areas of the adult and postnatally developing mouse CNS. Thy-1 mRNA expression was restricted to neurons; immunoreactivity was densely distributed throughout the neuropil of all regions examined, often delineated the neuronal plasmalemma, and labeled axons in white matter tracts of the brain and spinal cord. In adulthood, immunolabeling was regionally widespread and was present relatively homogeneously throughout all cell-dense layers of sensory-motor cortex, throughout most thalamic nuclei, globus pallidus, and spinal cord. Developmentally, however, Thy-1 expression and localization exhibited a spatially and temporally staggered sequence leading to the adult pattern. In sensory-motor cortex, Thy-1 expression in layer V preceded expression in other layers; in the barrel field, labeling of barrel septa preceeded a gradually increasing intensity of immunolabeling of barrel centers; in the thalamus, Thy-1 exhibited a differential onset and temporal pattern of expression across different nuclei associated with motor, sensory, or limbic systems; in the caudate nucleus, Thy-1 expression was greatest during the first postnatal week of life before declining during subsequent development. Taken together, the adult distribution and developmental patterns leading to it form a unique profile in comparison with other structurally related glycosyl-phosphatidylinositol (GPI)-anchored neural cell adhesion molecules. The pattern and timing of Thy-1 expression across layers and nuclei during early postnatal development are more complex than previously recognized, thus perhaps reflecting varied roles for Thy-1 in aspects of structural or functional maturation which proceed independently of the timing of neurogenesis, migration, and dendritic and axonal growth.