Tracing lymphopoiesis with the aid of a pTα-controlled reporter gene

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Abstract
A transgenic reporter mouse strain, which expressed the human CD25 (hCD25) surface marker as a reporter under the control of the pre-T cell receptor α(pTα) promoter, was used to identify lymphoid precursors that expressed pTα intracellularly. The hCD25 reporter marked intra- and extrathymic precursors of lymphocytes but not myeloid cells. The earliest intrathymic precursors were CD4loCD8−CD25−CD44+c-Kit+ cells that expressed elevated levels of Notch-1 mRNA. Clonogenic assays showed that the extrathymic precursors were common lymphoid progenitors (CLPs) that included CD19−, B220+, Thy1+ and CD4+ cells. Thus, the pTα reporter can be used to trace lymphopoiesis between CLPs and αβ T cells. The slower extinction of the hCD25 reporter compared to pTα enabled us to define points at which pTα− lineages branched off.