Immunoglobulin gene diversification by somatic hypermutation (SHM), class switch recombination (CSR), and gene conversion is dependent upon activation-induced cytidine deaminase (AID). AID is a single-stranded DNA specific cytidine deaminase that is expressed primarily in activated mature B lymphocytes. AID appears to catalyze DNA cytidine deamination of immunoglobulin heavy (IgH) and light cha...

Affinity maturation of the humoral response is mediated by somatic hypermutation of the immunoglobulin (Ig) genes and selection of higher-affinity B cell clones. Activation-induced cytidine deaminase (AID) is the first of a complex series of proteins that introduce these point mutations into variable regions of the Ig genes. AID deaminates deoxycytidine residues in single-stranded DNA to deoxyu...

Somatic mosaicism refers to the occurrence of two genetically distinct populations of cells within an individual, derived from a postzygotic mutation. In contrast to inherited mutations, somatic mosaic mutations may affect only a portion of the body and are not transmitted to progeny. These mutations affect varying genomic sizes ranging from single nucleotides to entire chromosomes and have bee...

Recent experiments have strongly suggested that the process of somatic mutation is linked to transcription initiation. It was postulated that a mutator factor loads onto the RNA polymerase and, during elongation, causes transcriptional arrest that activates DNA repair, thus occasionally causing errors in the DNA sequence. We report the analysis of the role of one of the known DNA repair systems...

Ig somatic hypermutation contributes to the generation of high-affinity Abs that are essential for efficient humoral defense. The presence of multiple point mutations in rearranged Ig V genes and their immediate flanking sequences suggests that the DNA repair system may not be working properly in correcting point mutations introduced to the restricted region of Ig genes. We examined the DNA rep...

To investigate the possible involvement of DNA repair in the process of somatic hypermutation of rearranged immunoglobulin variable (V) region genes, we have analyzed the occurrence, frequency, distribution, and pattern of mutations in rearranged Vlambda1 light chain genes from naive and memory B cells in DNA repair-deficient mutant mouse strains. Hypermutation was found unaffected in mice carr...

Activation-induced cytidine deaminase (AID) initiates Ig class switch recombination and somatic hypermutation by producing U:G mismatches in DNA. These mismatches also have the potential to induce DNA damage including double-stranded breaks and chromosome translocations; therefore, strict regulation of AID is important for maintaining genomic stability. In addition to transcriptional regulation...

Antibodies are glycoproteins produced by the immune system as a dynamically adaptive line of defense against invading pathogens. Very elegant and specific mutational mechanisms allow B lymphocytes to produce a large and diversified repertoire of antibodies, which is modified and enhanced throughout all adulthood. One of these mechanisms is somatic hypermutation, which stochastically mutates nuc...

Another piece in the hypermutation puzzle Studies with transgenic mice are beginning to define the minimal requirements for the somatic hypermutation of immunoglobulin genes that is critical in the production of high-affinity antibodies. One of the hallmarks of an advanced vertebrate immune system is the ability of the body to remember an invading organism, and to educate itself to respond more...

Somatic embryogenesis is the process by which somatic cells are induced into an embryogenic state, followed by differentiation into embryos. Somatic embryogenesis, in addition to being a method of propagation, can serve as an experimental tool for research into plant embryo development. This is a review of the current literature on in vitro plant somatic embryogenesis and the molecular advances...