DISTRIBUTION OF ALTERNATIVELY SPLICED CHICKEN C-MYB EXON 9A AMONG HEMATOPOIETIC TISSUES

The role of the c-myb proto-oncogene in cellular differentiation may b e regulated in part by alternative splicing of its mRNAs. Previously, two forms of alternative splicing of the chicken c-myb gene between ex ons 9 and 10 were described: one form utilizes the entire 360 base pai r (bp) exon 9A while a second form utilizes exon 9A' which consists of the 3' 150 bp of exon 9A. In this study the distribution among chicke n hematopoietic tissues of these two forms of alternative splicing was determined by Northern blot analysis using a probe specific for exon 9A. RNA species of 4.2 kilobases (kb) and 4.4 kb which contain exon 9A ' or exon 9A, respectively, were detected in each tissue tested. Quant itative analysis of the major 4.0 kb c-myb species and the c-myb speci es containing exon 9A and exon 9A' revealed that cells from yolk sac c ontained both the highest absolute and the highest relative levels of alternatively spliced c-myb mRNA, presumably because of the prepondera nce of immature erythroid cells in these preparations.