Jh. Coyle et al., PREDOMINANT USAGE OF THE PROXIMAL POLY(A) SITE IN ALPHA MESSENGER-RNAS IS NOT INTRINSIC TO THE 3' TERMINI, International immunology, 10(5), 1998, pp. 669-678
The maturation of IGM-expressing a cells to IgM-secreting plasma cells
is associated with both an increase in mu mRNA and the ratio of secre
ted to membrane forms of mu mRNA, In contrast, previous studies demons
trated that in vitro the secreted form of alpha mRNA (alpha s mRNA) pr
edominates regardless of the stage of a cell differentiation, The pres
ent study demonstrates that as mRNA predominates in both a cells deriv
ed from the germinal centers of murine Peyer's patches and in the func
tional IgA memory population, suggesting that in vitro events accurate
ly represent the generation of a secretory IgA response in vivo. Altho
ugh the predominant usage of the as poly(A) site is due to RNA process
ing, it does not depend on either the as poly(A) site, the 3' splice s
ite associated with the exon encoding the membrane exon of IgA (alpha
M) or the alpha M poly(A) sites. Analysis of the sequence of the intro
n between the as terminus and alpha M (alpha s-alpha M intron) demonst
rates the existence of several potential regulatory elements, Furtherm
ore, the effects of deletions within the alpha s-alpha M intron on 3'
terminus usage demonstrate that the predominant usage of the proximal
terminus is not strictly dependent on the length of the intron, Togeth
er with previous work, these observations support the idea that choice
of 3' terminus for ail Ig heavy chain genes is regulated by a similar
mechanism, but specific sequences within a heavy chain gene can impin
ge upon that mechanism.