AUTHOR=Bunnoy Anurak , Na-Nakorn Uthairat , Srisapoome Prapansak 

TITLE=Mystifying Molecular Structure, Expression and Repertoire Diversity of IgM Heavy Chain Genes (Ighμ) in Clarias Catfish and Hybrids: Two Novel Transcripts in Vertebrates

JOURNAL=Frontiers in Immunology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2022.884434

DOI=10.3389/fimmu.2022.884434

ISSN=1664-3224

ABSTRACT=<p>Two novel immunoglobulin heavy chain (<italic>Ighμ</italic>) transcripts encoding membrane-bound forms of IgM (mIgM) were discovered in bighead catfish<italic>, Clarias macrocephalus</italic>. The first transcript contains four constant and two transmembrane domains [Cμ1-Cμ2-Cμ3-Cμ4-TM1-TM2] that have never been reported in teleosts, and the second transcript is an unusual mIgM that has never been identified in any vertebrate [Cμ1-(Cδ2-Cδ3-Cδ4-Cδ5)-Cμ2-Cμ3-TM1-TM2]. Fluorescence <italic>in situ</italic> hybridization (FISH) in bighead catfish, North African catfish (<italic>C. gariepinus</italic>) and hybrid catfish revealed a single copy of <italic>Ighμ</italic> in individual parent catfish, while two gene copies were found in diploid hybrid catfish. Intensive sequence analysis demonstrated multiple distinct structural variabilities in the VH domain in <italic>Clarias</italic>, and hybrid catfish were defined and used to generate diversity with various mechanisms. Expression analysis of <italic>Ighμ</italic> in <italic>Aeromonas hydrophila</italic> infection of the head kidney, peripheral blood leukocytes and spleen revealed significantly higher levels in North African catfish and hybrid catfish than in bighead catfish.</p>