Genomic analysis of seahorse and pipefish suggests that the evolution of pregnancy may have coincided with modification of the adaptive immune system, according to a study. In vertebrates, a developing embryo must avoid being recognized as foreign tissue by an immune system attuned to attack foreign antigens. Olivia Roth and colleagues performed genomic analysis of seahorses and pipefishes to uncover links between the evolution of pregnancy and modification of the adaptive immune system. The authors analyzed the genomes of 12 species of seahorses and pipefishes representing a gradient of male pregnancy types, from external egg-carrying to full internal gestation with a placenta-like structure. The comparative analysis of genomes along this gradient revealed divergent genomic rearrangements in the major histocompatibility complex class II (MHC II) pathway of species that become fully pregnant; the MHC II pathway is an immune system component implicated in immunological tolerance. In seahorses, a portion of the MHC II molecule, CD74, was significantly different from mammals, likely affecting the molecule's binding ability. In pipefish, the authors found that the pathway was interrupted, likely preventing the molecule from presenting foreign antigens to immune cells. According to the authors, such natural inactivation of the MHC II pathway could provide a helpful model for studying immune deficiencies, given that pipefishes survive with a drastically altered adaptive immune system.
ARTICLE #19-16251: "Evolution of male pregnancy associated with remodeling of canonical vertebrate immunity in seahorses and pipefishes," by Olivia Roth et al.
MEDIA CONTACT: Olivia Roth, GEOMAR Helmholtz Centre for Ocean Research, Kiel, GERMANY; e-mail: oroth@geomar.de
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Proceedings of the National Academy of Sciences