The descent of the antibody-based immune system by gradual evolution

Abstract

The antibody-based immune system (AIS) is one of many means by which organisms protect themselves against pathogens and parasites. The AIS is present in jawed vertebrates (gnathostomes) but absent in all other taxa, including jawless vertebrates (agnathans). We argue that the AIS has been assembled from elements that have primarily evolved to serve other functions and incorporated existing molecular cascades, resulting in the appearance of new organs and new types of cells. Some molecules serving other functions have been appropriated by the AIS, whereas others have been modified to serve new functions, either after the duplication of their encoding genes or through the acquisition of an additional function without gene duplication. A few molecules may have been created de novo. The deployment and integration of the ready-made elements gives the impression of a sudden origin of the AIS. In reality, however, the AIS is an example of an organ system that has evolved gradually through a series of small steps over an extended period.gnathostomes ͉ agnathans ͉ immunoglobulin ͉ lymphocyte ͉ thymus

Myelin Tetraspan Family Proteins but No Non-Tetraspan Family Proteins Are Present in the Ascidian (Ciona intestinalis) Genome

“…Myelination requires a complex series of interactions between neurons and glial cells to foster a nervous system characterized by rapid, stable, and efficient transmission of nerve impulses from neuronal soma to terminal specializations. Perhaps, as in other systems such as jaws (Shigetani et al, 2002), the vertebrate endocrine system (Campbell et al, 2004), and antibodymediated immunity (Klein and Nikolaidis, 2005), preexisting pieces were connected into the myelination process by gnathostome ancestors. Although focus here is limited to the origins of a few glial proteins recruited for myelin assembly, one should realize that very many proteins are required both for the coordinated interactions between differentiating glial cell and growing axons that precede myelin sheath formation and for the formation of paranodal and nodal specializations.…”

Identification of pleiotropic genes and gene sets underlying growth and immunity traits: a case study on Meishan pigs

“…In addition, the gene HIF1A (Supplementary Table S1) is annotated as 'negative regulation of growth,' but this gene actually improves the immune capacity by activating embryonic hematopoiesis (Adelman et al, 1999). There are some pleiotropic genes that have the same functional direction as well -for example, the pleiotropic gene SIX1 (Supplementary Table S1) plays a positive role in many organs' development, including the thymus, which is very important for immune capacity (Klein and Nikolaidis, 2005), and the gene DAB2IP, which we defined in the third level with the GO term 'negative regulation of toll-like receptor 4 signaling pathway,' can also decrease the development speed of hepatocellular carcinoma (Zhang et al, 2012). For pleiotropic genes with the same functional direction, such as SIX1 and DAB2IP, it is much easier than genes that have different functional directions for breeding programs because the functional directions of the concerned traits are not incompatible.…”

Simple vertebrate models for chemical genetics and drug discovery screens: Lessons from zebrafish and Xenopus

“…Differences are also evident with the immune system. While the antibody-based, adaptive immune system is present in all jawed vertebrates (gnathostomes) (Klein and Nikolaidis, 2005), zebrafish and Xenopus differ considerably with regard to the presence of major lymphoid tissues, immunoglobulin gene organization, and the ability to perform immunoglobulin class switching (Du Pasquier et al, 1989;Traver et al, 2003). Bone marrow, gut-associated lymphoid nodules, and primitive lymph nodes are absent from zebrafish but present in Xenopus.…”