Expression of the SmB′ splicing protein in rodent cells capable of following an alternative RNA splicing pathway

Abstract

The expression of the SmB and SmB' spliceosome proteins in a variety of cell types and tissues has been investigated. Although SmB is found in all cells studied, the StuB' protein is found only in a small number of rodent cell types. The presence of this protein is correlated with the ability to utilize an alternative pathway of RNA splicing which is not available in most cell types. This is the first demonsIration of tissue specific expression of a protein component of the spliceosome and suggests a role for SmB' in the regulation of some cases of alternative RNA splicing.RNA splicing alternative; Autoimmuno antigen; Tissue-specific expression

Isolation of cDNA clones encoding the human Sm B/B′auto‐immune antigen and specifically reacting with human anti‐Sm auto‐immune sera

“…Since we have previously shown that this tissue expresses StuB but not SmB' [9], this RNA is likely to encode the SmB protein.…”

“…1.6 kb and 1.4 kb were detected the larger of which was present at considerably greater abundance. Since PCC3 cells in common with other EC cells express both the tissue specific StuB' protein and the constitutively synthesized SmB protein [9,10], it is likely that the larger transcript encodes the tissue specific B' protein. The RNA samples gave identical single bands when hybridized with probes specific for other RNA species such as that encoding cytochrome oxidase indicating that the difference in the pattern obtained with the K5-1 probe was not due to RNA degradation (not shown).…”

“…However, as we have recently shown [9] an acidic isotype of SmB' is expressed in a tissue specific manner in humans, its expression being confined to the same cell types as those expressing SmB' in rodents. Taken together these observations suggest a possible role for this tissue specific Sm protein in the regulation of alternative splicing allowing the production of different mRNAs from the same primary transcript in different cell types.…”

“…A/~gtll cDNA library prepared from the mRNA of HeLa cells (Clontech) was screened with the KSm5 antibody which reacts with both SmB and B' [7,9] according to the method of Huynh et al [13]. The single positive plaque obtained in this procedure was plaque purified by repeated rounds of screening at low density and was used to lysogenise bacteria of E. coli strain Y1089 [13].…”

“…In contrast the closely related SmB' protein is not detectable in most rodent cell types [5][6][7]. Recently, however, a protein of the size of SmB' and reacting with antibodies to SmB/B' has been shown to be expressed in a limited range of rodent ceils capable of following an alternative RNA processing pathway [9,10]. In particular such cells are capable of producing the mRNA encoding the calcitonin gene related peptide (CORP) from the primary transcript of the calcitonin/CGRP gene whilst most cells are capable of splicing this transcript to yield only the mRNA encoding calcitonin [11,12].…”