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

Abstract

The genetics of allorecognition has been determined from 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 improve the prediction of these phenotypes. Comparative genomics analyses were used to identify coding sequence differences in assembled chromosomal intervals of the ARC and genomic scaffold sequences between two incompatible H. symbiolongicarpus siblings from a backcross population. New IgSF-like genes are reported for the ARC, five of

A family of unusual immunoglobulin superfamily genes in an invertebrate histocompatibility complex

“…In nature, however, these genes might be as polymorphic as Alr1 and Alr2 . Such undiscovered allodeterminants could explain the appearance of unexpected allorecognition responses between outbred colonies ( 14 , 15 , 20 ).…”

“…Identifying additional Alr genes is of particular interest because the ARC probably contains at least one additional allodeterminant. Evidence for this comes from the fact that Alr1 and Alr2 can fail to predict allorecognition responses in field-collected colonies ( 14 , 15 , 20 ). The unidentified allodeterminant(s) likely reside in the ARC because genetic studies have shown that all Hydractinia allodeterminants, including dominant and codominant modifiers, are linked to Alr1 and Alr2 ( 21 ).…”