EVOLUTION AND EXPRESSION OF A BETA-LIKE GLOBIN GENE OF THE AUSTRALIANMARSUPIAL SMINTHOPSIS-CRASSICAUDATA

A beta-like globin gene was isolated from the Australian dasyurid mars upial Sminthopsis crassicaudata. Nucleotide-sequence analysis of promo ter and coding regions of the gene revealed that it was orthologous to eutherian early-expressed (epsilon, gamma, eta) beta-like globin gene s. Comparison of the conceptually translated sequence of the gene with a partial amino acid sequence of the adult beta-globin chain from S. crassicaudata provided evidence that the gene was not expressed in adu lt tissues. In addition, Northern analysis of RNA isolated from an emb ryo, pouch young, and adult bone marrow indicated that the gene was ex pressed predominantly in embryonic tissues and that there was a signif icant reduction in the expression of the gene within a day of birth. T hese results provide strong support for the hypothesis of Koop and Goo dman [Koop, B. F. & Goodman, M. (1988) Proc. Natl. Acad. Sci. USA 85, 3893-3897] that an embryonic beta-like globin gene existed prior to th e divergence of the eutherian and marsupial lineages and that this gen e was already differentiated with respect to its promoter regions and developmental expression. The observation that epsilon-globin mRNA was present at least until day 4 postpartum suggests that the epsilon-glo bin chain may play some role in influencing the physiological properti es of hemoglobin in S. crassicaudata neonates.