Expression of the Neuronal Surface Glycoprotein Thy‐1 Does Not Follow Appearance of Its mRNA in Developing Mouse Purkinje Cells

Abstract

In developing rodent nervous system, although the appearance of Thy‐1 mRNA, as seen by in situ hybridisation, is in general quickly followed by the appearance of immunohistochemically detectable protein, there are certain sites where a delay of several days occurs between expression of detectable message and protein. Mouse Purkinje cells exemplify this behaviour and are the dominant Thy‐1‐expressing cell in early postnatal cerebellum, so allowing quantitative, homogenate‐based methods to be used to test whether such a lag in protein expression does occur. Measurement of Thy‐1 mRNA (by slot blot) and protein (by radioimmunoassay) shows a substantial excess of Thy‐1 message, compared to protein accumulating in the tissue, during the first postnatal week, which is not found in tissues (rat cerebellum, and rat or mouse cerebrum) where no lag is apparent in appearance of Thy‐1 protein from the section‐based methods. The species of Thy‐1 mRNA produced by Purkinje cells does not appear to change during development, as assessed either in terms of its size (by northern blotting) or in the heterogeneous pattern of transcription initiation sites used (assessed by S1 nuclease protection analysis). Appearance of Thy‐1 protein in these cells, therefore, seems to be regulated post‐transcriptionally.