Answer:
The mechanism that allows naive T-cells to express CD45RA and memory CD4 T-cells to express CD45RO is alternative splicing of the CD45 gene.
Step-by-step explanation:
The CD45 gene, also known as the protein tyrosine phosphatase receptor type C (PTPRC) gene, encodes for the CD45 protein, which is a transmembrane protein expressed on the surface of T cells. Alternative splicing of the CD45 gene generates multiple isoforms of the CD45 protein, including CD45RA and CD45RO.
Naïve CD4 T cells express the CD45RA isoform, while memory CD4 T cells express the CD45RO isoform. This differential expression is achieved by alternative splicing of the CD45 pre-mRNA, which generates different exons that are included or excluded in the final mature mRNA. Naïve T cells predominantly express the CD45RA isoform, which is generated by inclusion of exons A, B, and C. Memory T cells, on the other hand, predominantly express the CD45RO isoform, which is generated by inclusion of exons B and C, but exclusion of exon A.
The CD45 protein is important for T cell development, activation, and signaling. The differential expression of CD45RA and CD45RO on naïve and memory CD4 T cells allows for distinct signaling and activation pathways in these cell types, contributing to their different functional properties.