Complementary DNA cloning of the alternatively expressed endothelial cell glycoprotein Ib beta (GPIb beta) and localization of the GPIb beta gene to chromosome 22.

Abstract

was most abundant in heart and brain, while GPIba and GPIX mRNA expression was found only in lung and placenta at very low levels. The broad distribution of GPIb# mRNA suggests that it may be playing a role different than or additional to its function in platelets. (J. Clin. Invest. 1994. 93:2417-2424

Alternative expression of platelet glycoprotein Ib(beta) mRNA from an adjacent 5' gene with an imperfect polyadenylation signal sequence.

“…Now we report a number of key differences from the sequence reported by Kelly et al (8) and in the fundamental conclusions derived from their work. We show that a unique gene located 5 Ј to the platelet GP Ib ␤ gene utilizes two different polyadenylation sites.…”

“…The smallest transcript is ‫ف‬ 1.0 kb and most likely corresponds to the mature GP Ib ␤ mRNA transcript seen in other megakaryocytic cell lines, megakaryocytes, and platelets (5,9). A larger, less abundant species is ‫ف‬ 3.5 kb and is not an expressed transcript seen in megakaryocytic RNA (8). To investigate the origin of the 3.5-kb transcript we prepared a CHRF-288-11 cDNA library and screened the library with the full-length platelet GP Ib ␤ cDNA.…”

“…cDNA cloning experiments for these three subunits of the complex have utilized megakaryocytic-like cell lines and without exception the reported coding sequences have been representative of the mRNA species present in the megakaryocyte and platelet (4)(5)(6). However, the megakaryocytic cell line CHRF-288-11 (7) is an exception containing two related mRNA species from the locus encoding the ␤ -subunit of GP Ib (GP Ib ␤ ) (8). A short 1.0-kb transcript is consistent with the size of the megakaryocytic mRNA encoding platelet GP Ib ␤ , whereas a longer transcript approximating 3.5 kb appears to be present in a wide variety of cell types but noticeably absent in megakaryocytes and other megakaryocytic-like cell lines (8,9).…”

“…However, the megakaryocytic cell line CHRF-288-11 (7) is an exception containing two related mRNA species from the locus encoding the ␤ -subunit of GP Ib (GP Ib ␤ ) (8). A short 1.0-kb transcript is consistent with the size of the megakaryocytic mRNA encoding platelet GP Ib ␤ , whereas a longer transcript approximating 3.5 kb appears to be present in a wide variety of cell types but noticeably absent in megakaryocytes and other megakaryocytic-like cell lines (8,9).…”

“…Kelly et al reported the cloning of a cDNA hybridizing to the platelet GP Ib ␤ cDNA and suggested the 3.5-kb transcript expressed by endothelial cells possesses the potential to synthesize a novel 45-kD protein containing a carboxyl terminus of platelet GP Ib ␤ polypeptide sequence (8). However, a number of fundamental concerns were raised by their report.…”