Differential gene expression in CD45 cells at para-aortic foci stage of chicken haematopoiesis.

Para-aortic foci of chicken embryos at 6-7 days of development are considered to provide a microenvironment for haematopoietic stem cell proliferation and initial differentiation similar to that of fetal liver in mammals. Here, we have investigated the genes involved in this process by constructing and analysing a subtractive cDNA library from CD45(+) cells in para-aortic region. Among 394 analysed clones 99 distinct genes were identified by sequence homology search. Classification of the identified genes according to biological processes revealed that innate immunity-related genes are highly expressed at this stage. This can be explained by the presence of yolk sac-derived macrophages in the original tissue sample but also by the indiscriminate expression of multiple lineage-specific genes in haematopoietic stem cells and primitive progenitors. Differentially expressed genes related to transcription, signalling and lymphocyte functions are potential candidates involved in lineage commitment.