Expression of lymphoid lineage-specific genes in midgestation (9-13 dpc) mouse embryos.

(A) Gene transcript levels of rag-2, VpreB, λ5, and β-actin in sequential samples of embryo lymphohematopoietic progenitor–containing areas (YS, P-Sp/AGM, liver, and blood), as detected by semiquantitative RT-PCR. After hybridization and densitometric quantification, the means of the relative message levels obtained for rag-2, VpreB, and λ5 were referred to those calculated in simultaneous 13-dpc liver PCR amplifications (as a maximum; n = 6-10 independent samples per organ per gestational day). These results are expressed by the +/− symbols in the figure, which represent −, < 1%; +/−, 1%-10%; +, 10%-40%; ++, 41%-70%; +++, 71%-100%. (B) Sensitivity threshold of λ5- and VpreB-specific RT-PCRs calculated in a titration of the 70Z/3 pre–B-cell line up to the single-cell level. Densitometric quantification of the specific signals obtained in 3 independent experiments; means ± SD are shown.