Evidence of IgY subclass diversification in snakes: evolutionary implications

Area of Science:

• Immunology
• Evolutionary Biology
• Zoology

Background:

• Mammalian immunoglobulin G (IgG) and immunoglobulin E (IgE) are hypothesized to originate from nonmammalian tetrapod IgY.
• Reptiles and birds, closely related to mammals, have not shown IgY subclass diversification, leaving a gap in understanding antibody evolution.

Purpose of the Study:

• To investigate the presence and structure of immunoglobulin Y (IgY) encoding genes in snakes.
• To explore the evolutionary relationship between snake IgY and mammalian immunoglobulins.

Main Methods:

• Identification and sequencing of IgY (υ) genes in Elaphe taeniura and Python molurus bivittatus.
• Analysis of the exon structure of identified IgY genes.
• Development of monoclonal antibodies (mAbs) against snake IgY subclasses.
• Detection of IgY isoforms in snake serum.

Main Results:

• The first evidence of multiple IgY-encoding (υ) genes in snakes was reported, with two found in E. taeniura and three in P. molurus bivittatus.
• One IgY gene in P. molurus bivittatus exhibited a unique structure lacking the H chain C region 2 exon, resembling mammalian γ genes.
• Both IgY1 and IgY2 of E. taeniura were expressed in serum as full-length and C-terminally truncated isoforms, not due to alternative splicing or termination.
• Mu (μ) and delta (δ) genes were identified, but alpha (α) genes were absent in both snake species.

Conclusions:

• The discovery of multiple IgY genes and a unique gene structure in snakes provides crucial insights into the diversification of IgY subclasses.
• These findings contribute significantly to understanding the evolutionary trajectory of immunoglobulin genes in tetrapods, bridging the gap between nonmammalian and mammalian antibody systems.