Immunoglobulin mu- and gamma-ribonucleic acid sequences in thymocytes and splenocytes from normal and hyperimmune mice.

Abstract

The immunoglobulin heavy-chain ribonucleic acid (RNA) repertoire of mouse thymocytes was examined. Previously, this laboratory reported immunoglobulin alpha-chain RNA sequences in mouse thymocytes [Near, R. I., & Storb, U. (1979 Biochemistry, 18, 964]. We have extended these studies to encompass mu, gamma 2b, and gamma 1 heavy-chain RNA sequences, mu-, gamma 2b-, and gamma 1-messenger RNAs (mRNAs) were purified from myelomas to 45, 22, and 54% purity, respectively. Each of these mRNAs faithfully translated into the appropriate immunoprecipitable protein in a reticulocyte lysate translation system. The gamma 1-mRNA translated into two major immunoprecipitable products of about 52 500 and 51 000 daltons while mu- and gamma 2b-mRNAs yielded only a single major protein. Complementary deoxyribonucleic acids (cDNAs) prepared from the mRNAs were used as hybridization probes and revealed the presence of about 70 mu-RNA sequences per average thymocyte as determined by hybridization kinetics, while gamma 1 and gamma 2b sequences were at the limits of detection. The mu-RNA sequences are present in the cytoplasm and are greater than 50% polyadenylated. Upon hyperimmunization of mice with sheep red blood cells, gamma 1-RNA in splenocytes increased by about 100-fold while only slightly increasing in thymocytes. mu and gamma 2b increased 2-3-fold in splenocytes and only slightly in thymocytes. The results argue against RNA sequences appearing in thymocytes due to contamination with peripheral confirmed with cloned cDNA probes. Thymocyte RNA analyzed by Northern blots displayed bands of the same size as those in splenocyte RNA or in purified mRNA when hybridized to mu, gamma 2b and alpha cloned probes. Also, K light-chain RNAs of the same size were found in spleen and thymus by using a cloned K-DNA probe. The results are consistent with the thymus containing mu-, alpha-, and K- and small amounts of gamma 1- or gamma 2b-RNAs coding for heavy- and light-chain-like proteins which may play a role in T-cell function.