The evolutionarily conserved avian Aiolos gene encodes alternative isoforms

Aiolos is an Ikaros-related lymphoid regulatory protein involved in B cell development and function. To evaluate the role of Aiolos in avian B lymphopoiesis, we have cloned and characterized the first non-mammalian Aiolos ortholog in the avian. In sharp contrast to the avian Ikaros, expressed already at the multipotential stage and prior to the colonization of the lymphoid rudiments, Aiolos transcripts were not expressed in early ontogeny and were first detected in cells isolated from the embryonic bursa of Fabricius and thymus. In accordance with Ikaros, the avian Aiolos is also highly related to the mammalian homolog, thus suggesting an evolutionarily conserved function in lymphocyte development. Interestingly, in contrast to the mammalian Aiolos, at least one alternatively spliced form of avian Aiolos is detected in addition to the primary full-length transcript. Both of these alternate transcripts are expressed in bursa, thymus and peripheral lymphoid cells, and no major differences in the expression were detected during lymphocyte development. Furthermore, avian Aiolos is clearly expressed at various stages of B cell development, thus supporting recent evidence for the importance of Aiolos in B cell development and function.