No abstract

We have generated Thy-1

Hybrid human--mouse Thy-1.1 genes were injected into pronuclei of Thy-1.2 mice to produce transgenic animals. A hybrid gene composed of the 5' part of the mouse Thy-1.1 gene combined with the 3' human untranslated regions was expressed abnormally in the kidney podocytes, which resulted in severe protein-uria and subsequent death in several founder mice. A hybrid Thy-1 gene composed of the human coding region with the 5' and 3' flanking regions of the mouse gene was expressed abnormally in a different part of the kidney (the tubular epithelia), which resulted in a proliferative kidney disorder. In addition, a neoplasm was found in the brain of one of these mice. These results show that the Thy-1 protein can play an important role in the activation, proliferation, and differentiation of many different cell types.

The cell surface glycoprotein, Thy-1, is present on Purkinje cells at birth, so allowing Thy-1 immunohistochemistry to demonstrate the final stage of migration and the transition to dendritic growth of these cells. In the most caudal lobule of the cerebellar cortex of the newborn rat, migrating Purkinje cells are found. These have a prominent process (up to 50 micron long) from which fine filopodia project, presumably sensing the environment in front of the cell. These cells are orientated tangentially, at right angles to the radial orientation they assume for dendritic growth. Strong Thy-1 labelling is found not only on their surface, but also on a cytoplasmic cap above the presumed leading pole of the nucleus. More rostrally in the cerebellar cortex, Purkinje cells arrive up to 3 days before birth and are quiescent until the postnatal development of their dendritic tree. At birth and during early postnatal periods a rounded cell is found with little cytoplasm; Thy-1 staining labels its surface and the fine processes which emanate from it. Such cells coexist with other Thy-1-positive Purkinje cells with more developed surface orientated processes. Even as early as the day of birth these fine processes cross the molecular layer and contact the lower level of the external granule layer. Orientated dendritic growth appears to occur by a selective thickening of these processes and a massive apical protrusion of intensely Thy-1-positive cytoplasm. The whole of the Purkinje cell surface membrane exhibits high levels of Thy-1 throughout dendritic growth and synaptogenesis, and cytoplasmic antigen is prominent during the period of greatest growth. Thy-1 is also found on the neurons of the deep cerebellar nuclei, and is seen transiently on Golgi interneurons. High levels of the antigen are present on blood vessels and choroid plexus at birth but are lost from these structures over the first 2 postnatal weeks.

The distribution of the cell surface glycoprotein Thy-1 in the P.N.S. of adult rats was examined using immunohistochemical and experimental techniques. In the hypoglossal nerve the pattern of Thy-1 labelling suggested the antigen was on the plasma membrane of all axons, not only in their major myelinated course but also on their fine terminal branches and at the motor end plate itself. Similarly in other peripheral nerves examined [phrenic and vagus nerves, dorsal and ventral roots, and both the preganglionic and postganglionic trunks of the superior cervical ganglion (SCG) and the submandibular ganglion] Thy-1 was always associated with axons, but the resolution obtained with immunohistochemical techniques was not in itself sufficient to exclude the possibility that the antigen was on the surface of the ensheathing Schwann cell where it apposed the axons. However, in the hypoglossal nerve the antigen was found to accumulate proximal to a ligation of the nerve, suggesting it was made by the neurons and transported down the nerve by axoplasmic flow. This impression was supported by examining neuronal cell bodies in the SCG, dorsal root ganglia and submandibular ganglion, all of which contain readily detectable cytoplasmic Thy-1. In the SCG this cytoplasmic antigen was shown to include the pool of newly synthesized Thy-1. It was increased by treatment of the ganglion with colchicine, and decreased by cycloheximide. Conversely, treatment of hypoglossal nerve trunk with colchicine did not lead to the appearance of the antigen around the non-neuronal perikarya. It is therefore concluded that in those parts of the adult rat P.N.S. examined, Thy-1 is made by neurons and occurs generally on the plasma membrane of axons.