Expression and Temperature-Dependent Regulation of the Beta₂-Microglobulin (Cyca-B2m) Gene in a Cold-Blooded Vertebrate, the Common Carp (Cyprinus carpio L.)

Abstract

Expression of beta₂-microglobulin (β ₂m) in the common carp was studied using a polyclonal antibody raised against a recombinant protein obtained from eukaryotic expression of the Cyca-B2m gene. β ₂m is expressed on peripheral blood Ig⁺ and Ig^- lymphocytes, but not on erythrocytes and thrombocytes. In spleen and pronephros, dull- and bright-positive populations could be identified correlating with the presence of erythrocytes, thrombocytes, and mature leucocytes or immature and mature cells from the lympho-myeloid lineage, respectively. Thymocytes were shown to be comprised of a single bright-positive population. The Cyca-B2m polyclonal antiserum was used in conjunction with a similarly produced polyclonal antiserum to an MHC class I (Cyca-UA) α chain to investigate the expression of class I molecules on peripheral blood leucocytes (PBL) at different permissive temperatures. At 12℃, a temporary downregulation of class I molecules was demonstrated, which recovered to normal levels within 3 days. However, at 6℃, a lasting absence of class I cell-surface expression was observed, which could be restored slowly by transfer to 12C. The expression of immunoglobulin molecules on B cells was unaffected by temperature changes. The absence of the class cell-surface expression was shown to be the result of a lack of sufficient Cyca-B2m gene transcription, although Cyca-UA mRNA was present at comparable levels at all temperatures. This suggests that class I expression is regulated by a temperature-sensitive transcription of the Cyca-B2m gene.

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