Selective Transgenic Expression of Mutant Ubiquitin in Purkinje Cell Stripes in the Cerebellum

Abstract

The ubiquitin-proteasome system (UPS) is one of the major mechanisms for protein breakdown in cells, targeting proteins for degradation by enzymatically conjugating them to ubiquitin molecules. Intracellular accumulation of ubiquitin-B⁺¹ (UBB⁺¹), a frameshift mutant of ubiquitin-B, is indicative of a dysfunctional UPS and has been implicated in several disorders, including neurodegenerative disease. UBB⁺¹-expressing transgenic mice display widespread labeling for UBB⁺¹ in brain and exhibit behavioral deficits. Here, we show that UBB⁺¹ is specifically expressed in a subset of parasagittal stripes of Purkinje cells in the cerebellar cortex of a UBB⁺¹-expressing mouse model. This expression pattern is reminiscent of that of the constitutively expressed Purkinje cell antigen HSP25, a small heat shock protein with neuroprotective properties.

Keywords: Cerebellum; Heat shock protein 25; Purkinje cell stripes; Ubiquitin-B+1; Ubiquitin-proteasome system; Zebrin II.

Fig. 1

Expression pattern of mutant ubiquitin (UBB⁺¹) in the mouse cerebellum. Distribution of UBB⁺¹ in the cerebellum of a UBB⁺¹-expressing transgenic mouse line. A coronal section reveals restricted expression of UBB⁺¹ in parasagittal stripes of Purkinje cells (PCs) in the vermis of the cerebellar cortex (a and b). A sagittal overview shows expression of UBB⁺¹ in lobules VI, VII, IX, and X (c). IC inferior colliculus, NTS nucleus of the solitary tract. Asterisk denotes additional UBB⁺¹ expression in the cerebellar hemisphere. Scale bars a and c 500 μm, b 50 μm

Fig. 2

Co-expression of mutant ubiquitin (UBB⁺¹) and HSP25 in Purkinje cell (PC) stripes. UBB⁺¹ is expressed in a subset of zebrin II-positive PC stripes in the cerebellum of a UBB⁺¹-expressing mouse line (a–c). Co-immunofluorescence (d–f) shows co-expression of UBB⁺¹ and HSP25. All sections are in the coronal plane (lobules IX–X). Scale bars a–c 200 μm, d–f 100μm