Mapping of prolactin and tumor necrosis factor-beta genes on human chromosome 6p using lymphoblastoid cell deletion...

A collection of human B lymphoblastoid cell lines (LCLs) was used to map two genetic sequences for which polymorphism had not been identified: human prolactin (PRL) and tumor necrosis factor-beta (TNFB). The LCLs have overlapping deletions on chromosome 6p produced by gamma-irradiation of LCL 721. After using two chromosome 6p sequences for which LCL 721 is heterozygous to validate our scanning densitometry (SD) method for inferring gene copy number, SD was used to map TNFB and PRL. TNFB maps to the interval between the C4 complement and HLA-B loci within the MHC on chromosome 6p. PRL lies within the 6p21.3-6p22.2 interval distal to HLA-C. We found that LCL 721 is heterozygous for PRL DNA fragment lengths generated by HpaII but not MspI digestion, indicating that the two copies of PRL in LCL 721 are differentially methylated. This novel methylation RFLP was used to corroborate the region PRL assignment.