Expression of MhcCyca class i and class ii molecules in the early life history of the common carp (Cyprinus carpio L.)

In this study transcription of class I α chain ( Cyca-UA), β 2-microglobulin ( Cyca-B2m) and class II α ( Cyca-DXA) and β ( Cyca-DAB) during the early stages of embryo development was investigated by semi-quantitative PCR. No transcripts of the genes under investigation were detected in the unfertilized egg. The expression of the genes encoding for the class II molecules revealed to be synchronized starting at day 1, unlike those for the class I molecules. Transcription of Cyca-B2m was first detected at day 7, whereas Cyca-UA was already present on day 1. This discrepancy would suggest absence of class I molecules during early development. The transcription of the Mhc genes in lymphoid organs was well established on day 21, with the exception of the spleen. In later stages of ontogeny cell surface expression of class I molecules was studied using polyclonal antibodies to Cyca-UA and Cyca-B2m in conjunction with detection of surface Ig. In week 3–10 Cyca-B2m was found on a higher percentage of cells from pronephros, spleen and thymus compared to Cyca-UA, suggesting the use of an alternative class I α chain. In the thymus, unlike the other organs, this difference remained present in the adult stage. The most likely candidates are α chains encoded by non-classical class I genes.