Abstract
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.