Genomic structure and expression of immunoglobulins in Squamata

• Identification of immunoglobulins from genomes of 4 Squamata species and differential gene expression from 18 others.
• Show evidence that some Squamata lineages possess more than one Cμ gene.
• Demonstrate the existence of two evolutionary lineages of IgY.
• Show that while all Squamata species possess the λ light chain, only Iguanidae species possess the κ light chain.

The Squamata order represents a major evolutionary reptile lineage, yet the structure and expression of immunoglobulins in this order has been scarcely studied in detail. From the genome sequences of four Squamata species (Gekko japonicus, Ophisaurus gracilis, Pogona vitticeps and Ophiophagus hannah) and RNA-seq datasets from 18 other Squamata species, we identified the immunoglobulins present in these animals as well as the tissues in which they are found. All Squamata have at least three immunoglobulin classes; namely, the immunoglobulins M, D, and Y. Unlike mammals, however, we provide evidence that some Squamata lineages possess more than one Cμ gene which is located downstream from the Cδ gene. The existence of two evolutionary lineages of immunoglobulin Y is shown. Additionally, it is demonstrated that while all Squamata species possess the λ light chain, only Iguanidae species possess the κ light chain.