Rearrangement of Ig genes in avian B cell precursors

The bursa of Fabricius is essential for normal development of chicken B lymphocytes. To analyze early (pre-bursal) stages of B cell development, day 14e-15e chick embryo bone marrow cells were transformed with the avian REV-T(CSV) retrovirus and cloned. Some clones contained rearranged and expressed immunoglobulin genes, demonstrating that the bursal microenviornment is not required for immunoglobulin gene rearrangement and expression. In order to examine the sequence of immunoglobulin gene rearrangements during chicken B cell development, day 12e embryo bursal cells were transformed using REV-T(CSV). Clones containing either rearranged immunoglobulin light chain or rearranged immunoglobulin heavy chain genes demonstrated that chicken immunoglobulin variable region gene rearrangement occurs stochastically rather than sequentially (as is the case in mammalian species). Furthermore, sequencing of chicken immunoglobulin variable region genes demonstrated that allelic variations arise as a consequence of germ line gene conversion rather than point mutation