Dissecting alternative splicing in the formation of Miltenberger glycophorin subtype III (GYP.Mur)

Area of Science:

• Genetics
• Molecular Biology
• Hematology

Background:

• Miltenberger subtype III (Mi.III, GP.Mur) is a significant red cell phenotype in Southeast Asian transfusion medicine.
• GP.Mur is thought to arise from homologous recombination between glycophorin A (GYPA) and glycophorin B (GYPB).
• GP.Mur differs from GYPB by seven nucleotides near the 3' exon 3 region.

Purpose of the Study:

• To investigate how specific nucleotide variations between GP.Mur and GYPB influence the splicing of exon 3.
• To elucidate the molecular mechanism underlying GP.Mur formation and its impact on red blood cell phenotypes.

Main Methods:

• Minigene constructs of GYP.Mur and GYPB were created, spanning exons 2 to 4.
• Point mutations were introduced into GYP.Mur-like constructs to mimic GYPB sequences.
• Splicing efficiency of exon 3 was assessed using a heterologous expression system.

Main Results:

• The GYP.Mur minigene successfully spliced exons 2, 3, and 4.
• The GYPB minigene exclusively spliced exons 2 and 4, excluding exon 3.
• A single nucleotide change at the 5' splice site of glycophorin intron 3 was identified as the key determinant for exon 3 splicing.
• Other nucleotide variations between GYP.Mur and GYPB had minimal impact on exon 3 splicing.

Conclusions:

• The splicing patterns of glycophorin B-A-B hybrids (GYP.Mur, GYP.BUN) and the unsplicing of GYPB strictly adhere to the GU-AG splicing rule.
• The 5' splice site nucleotide variation is critical for the functional expression of the GP.Mur phenotype.