Immunological Diversity Is a Cornerstone of Organismal Defense and Allorecognition across Metazoa

Local Genomic Instability of the SpTransformer Gene Family in the Purple Sea Urchin Inferred from BAC Insert Deletions

The SpTransformer (SpTrf) gene family in the purple sea urchin, Strongylocentrotus purpuratus, encodes immune response proteins. The genes are clustered, surrounded by short tandem repeats, and some are present in genomic segmental duplications. The genes share regions of sequence and include repeats in the coding exon. This complex structure is consistent with putative local genomic instability. Instability of the SpTrf gene cluster was tested by 10 days of growth of Escherichia coli harboring bacterial artificial chromosome (BAC) clones of sea urchin genomic DNA with inserts containing SpTrf genes. After the growth period, the BAC DNA inserts were analyzed for size and SpTrf gene content. Clones with multiple SpTrf genes showed a variety of deletions, including loss of one, most, or all genes from the cluster. Alternatively, a BAC insert with a single SpTrf gene was stable. BAC insert instability is consistent with variations in the gene family composition among sea urchins, the types of SpTrf genes in the family, and a reduction in the gene copy number in single coelomocytes. Based on the sequence variability among SpTrf genes within and among sea urchins, local genomic instability of the family may be important for driving sequence diversity in this gene family that would be of benefit to sea urchins in their arms race with marine microbes.

Multiple Alr genes exhibit allorecognition-associated variation in the colonial cnidarian Hydractinia

The genetics of allorecognition has been studied extensively in inbred lines of Hydractinia symbiolongicarpus, in which genetic control is attributed mainly to the highly polymorphic loci allorecognition 1 (Alr1) and allorecognition 2 (Alr2), located within the Allorecognition Complex (ARC). While allelic variation at Alr1 and Alr2 can predict the phenotypes in inbred lines, these two loci do not entirely predict the allorecognition phenotypes in wild-type colonies and their progeny, suggesting the presence of additional uncharacterized genes that are involved in the regulation of allorecognition in this species. Comparative genomics analyses were used to identify coding sequence differences from assembled chromosomal intervals of the ARC and from genomic scaffold sequences between two incompatible H. symbiolongicarpus siblings from a backcross population. New immunoglobulin superfamily (Igsf) genes are reported for the ARC, where five of these genes are closely related to the Alr1 and Alr2 genes, suggesting the presence of multiple Alr-like genes within this complex. Complementary DNA sequence evidence revealed that the allelic polymorphism of eight Igsf genes is associated with allorecognition phenotypes in a backcross population of H. symbiolongicarpus, yet that association was not found between parental colonies and their offspring. Alternative splicing was found as a mechanism that contributes to the variability of these genes by changing putative activating receptors to inhibitory receptors or generating secreted isoforms of allorecognition proteins. Our findings demonstrate that allorecognition in H. symbiolongicarpus is a multigenic phenomenon controlled by genetic variation in at least eight genes in the ARC complex.

Non-traditional roles of immune cells in regeneration: an evolutionary perspective

Immune cells are known to engage in pathogen defense. However, emerging research has revealed additional roles for immune cells, which are independent of their function in the immune response. Here, we underscore the ability of cells outside of the adaptive immune system to respond to recurring infections through the lens of evolution and cellular memory. With this in mind, we then discuss the bidirectional crosstalk between the immune cells and stem cells and present examples where these interactions regulate tissue repair and regeneration. We conclude by suggesting that comprehensive analyses of the immune system may enable biomedical applications in stem cell biology and regenerative medicine.