Murine B cell differentiation is accompanied by programmed expression of multiple novel beta-galactoside alpha2, 6-sialyltransferase mRNA forms.
ST6Gal I (beta-galactoside alpha2,6-sialyltransferase, ST6N) elaborates the ubiquitously expressed alpha2,6-sialyl linkage. A number of ST6Gal I mRNA isoforms, differing only in their 5'-UT regions, is transcribed from a single mouse gene, Siat1. In B-lineage cells, alpha2,6-sialic acid serves as extracellular ligand for CD22, a participant in cell activation via an intracellular signaling network of tyrosine kinases and SHP phosphastase. Activation and terminal differentiation of mature B cells into plasma cells is accompanied by the appearance of at least four distinct ST6Gal I mRNA isoforms. Resting splenic B-lymphocytes isolated from 8-12 wk C56Bl/6 mice expressed almost exclusively the Exons Q+O-containing form, which is the likely homolog to the previously documented human Y+Z and rat -1+0 forms. In vitro activation using recombinant CD40-ligand and conditioned media from T-helper cells resulted in a 2- to 3-fold elevation of overall ST6Gal I mRNA abundance by Day 3. This coincided with repression of the Q+O form, and appearance of three new isoforms containing 5'-untranslated sequences X(1), X(2), or X(3). The X(1)form persisted through Day 10, when the transition of B cells to plasma cells was completed as evidence by disappearance of CD22 mRNA. In contrast, the X(2)form only transiently appeared at Day 3 and declined to barely detectable levels by Day 7. Expression of the X(3)form, a minor mRNA form, paralleled the X(2)form. The divergent 5'-UT exons are dispersed over 69 kb of linear genomic space of Siat1. Mutually exclusive utilization of these 5'-UT exons in transcripts predicts separate and distinct promoter regulatory regions for each mRNA isoform.
Wuensch
S A
SA
Department of Molecular and Cellular Biology, Roswell Park Cancer Institute, Buffalo, NY 14263, USA.
Huang
R Y
RY
Ewing
J
J
Liang
X
X
Lau
J T
JT
D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology*; D001483:Base Sequence; D002454:Cell Differentiation / Q000235:genetics*; D004247:DNA; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics*; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012799:Sialyltransferases / Q000235:genetics*; D013154:Spleen / Q000166:cytology; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase
D012333:RNA, Messenger; D004247:DNA; D012799:Sialyltransferases; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase