Differential expression of murine adult hemoglobins in early ontogeny.

Mice with a mutation at the Hbbs, beta-globin locus, were used to study the relative levels of beta-s2major (mutant) and beta-sminor globins specified by the mutant Hbbs2 haplotype during development. At 11.5 days of gestation, beta-sminor comprised over 80 percent and beta-s2major under 20 percent of the adult beta-globin. The relative level of beta-sminor decreased through fetal development; at birth beta-sminor represented 33.7 percent of the beta-globin. The adult values of 29.0 percent beta-sminor and 71.0 percent beta-s2major globin are expressed in mice six days after birth. Because the two beta-globin genes are expressed in mice of the Hbbs2 haplotype, both the beta-smajor and beta-sminor genes are presumably expressed in mice of the Hbbs haplotype. Expression of the beta-sminor gene is elevated to 35.6 percent in adult Hbbs2/Hbbs2 mice that have been bled repeatedly. Thus, the 5' beta-s2major and 3' beta-sminor genes of the Hbbs2 haplotype and, presumably the 5' beta-smajor and 3' beta-sminor genes of the Hbbs haplotype, are regulated independently and are homologous to the 5' beta-dmajor and 3' beta-dminor genes of the Hbbd haplotype. Mice of the Hbbs2 haplotype are better suited than mice of the Hbbd haplotype for studying the mechanisms of hemoglobin switching because with Hbbs2 each of the three embryonic and two adult hemoglobins can be separated by electrophoresis.