Transgene construct and expression of PLAP mRNA and protein in adult mice.

(A) Mouse c-mpl gene (top) with sequences of the 5′-upstream region (enlarged) aligned with the c-mpl/PLAP transgene. Black box represents c-mpl exon 1. Start codons for c-mpl and PLAP are highlighted. The transgene retains most of the c-mpl 5′-untranslated region. (B) Transgenic construct and position of the riboprobe used for the detection of PLAP mRNA expression. Tissues of mice heterozygous for the PLAP transgene were analyzed: bm, bone marrow; ln, mesenteric lymph node; pa, pancreas; br, brain; lu, lung; li, liver; sp, spleen; ki, kidney; ht, heart; th, thymus. Riboprobes for PLAP, c-mpl, and HPRT were mixed to allow the simultaneous detection of PLAP, endogenous c-mpl, and HPRT mRNAs. (C) PLAP protein expression in platelets and megakaryocytes of wild-type (wt) and transgenic (TG) mice. Dark staining indicates PLAP activity. Note that platelets have aggregated in the blood smear from TG. Magnification × 500.