Regulation of immunoglobulin D synthesis in murine neonatal B lymphocytes.

We analyzed the regulatory basis for the lower expression of immunoglobulin D (IgD) in lymphocytes from neonatal mice of various ages. The results indicate that the relative transcriptional rate of RNA for delta chains is similar to adult levels even in cells which have not started to express IgD. These results suggest that very early after the initiation of mu gene transcription, a defined fraction of polymerases is programmed to progress through the termination site to the delta exons regardless of the developmental stage of the cell. Similar results were obtained from adult CBA/N mice whose spleens contain a large fraction of cells expressing low levels of IgD. On the other hand, the relative steady state level of mRNA in neonatal lymphocytes is approximately half of that in adults, suggesting that there may be differences in the processing or stability of the nascent transcript. In addition, measurements of the in vivo translation rate show that an inefficient delta polypeptide chain processing machinery in neonatal lymphocytes is also an important factor contributing to the reduced expression of IgD.