Gene organization of haplotypes expressing two different C4A allotypes

Area of Science:

• Immunogenetics
• Molecular Biology

Background:

• The complement system, particularly the C4 gene, plays a crucial role in immune responses.
• Understanding the complex gene organization of C4 haplotypes is essential for deciphering their functional implications.
• Previous studies have identified various C4 allotypes and null alleles, but their precise genomic arrangement remains an area of investigation.

Purpose of the Study:

• To elucidate the gene organization of C4 haplotypes associated with specific C4A allotypes and a C4B null allele.
• To determine the presence and arrangement of C4A, C4B, and 21-hydroxylase genes within these haplotypes.
• To propose a model explaining the occurrence of C4 null alleles in haplotypes with dual C4 loci.

Main Methods:

• Southern blot analysis was employed to examine the gene structure.
• cDNA probes specific for C4A and C4B loci were utilized.
• Restriction enzymes generating locus-specific fragments were used to differentiate C4A and C4B genes.

Main Results:

• Haplotypes C4A3A2BQ0 and C4A3A6BQO were found to possess both C4A and C4B loci.
• Evidence suggests that the C4B locus in these haplotypes may express a C4A protein.
• The C4A3A6BQO haplotype contains both 21-hydroxylase A and 21-hydroxylase B genes, indicating a common C4A, 21-OH A, C4B, 21-OH B gene organization.

Conclusions:

• The presence of both C4A and C4B loci, along with a C4B null allele, indicates a complex gene arrangement in studied haplotypes.
• The findings suggest potential functional implications where the C4B locus might contribute C4A protein expression.
• A model is proposed to explain the genetic basis of C4 null alleles within haplotypes containing two C4 loci, advancing the understanding of complement gene regulation.