B219/OB-R long isoform is expressed early in hematopoietic tissue. B219/OB-R long form is the full-length6 and type 3 isoform receptor molecule2 are evaluated by PCR in samples from (A) murine ES cells from 0 to 6 days of differentiation, (B) yolk sac (YS) from d8 to d18 murine embryos, and (C) fetal liver (FL) from d13 to d18 murine embryos. MW, 100-bp molecular-weight markers; BM, adult bone marrow.