Expression of the FcRn receptor (α and β) gene homologues in the intestine of suckling brushtail possum ( Trichosurus vulpecula) pouch young

Abstract

The neonatal IgG transporter FcRn consists of two chains, FcRn α and β (also known as β 2 microglobulin), and is involved in transferring IgG molecules across both mammary and intestinal epithelial cells. Developmental changes in FcRn IgG α and β chain mRNA levels were investigated in the gut of brushtail possum ( Trichosurus vulpecula) pouch young (PY) using Northern hybridisation. FcRn α transcripts were detected in the PY proximal intestine at all times examined, between days 1 and 195 of post-natal life, with increased levels detected from around day 110. The β 2 microglobulin transcript levels in the PY proximal intestine were low to undetectable until day 110 of post-natal life and then increased dramatically after day 159. Both the FcRn α and β gene transcripts were detected in a wide range of tissues in the adult possum (>365 days). Genomic sequences located 5′ to the start of transcription of the FcRn α and β 2 microglobulin genes were cloned and analysed for predicted cis-acting transcription control elements. Both the FcRn α and β 2 microglobulin genomic sequences contained STAT5 binding motifs consistent with the transcription of both genes being modulated by prolactin. Using in situ hybridisation, the FcRn α and β 2 microglobulin transcripts were localised to the epithelial cells of the PY intestine. However, no prolactin receptor transcripts were detected in the same epithelial cells suggesting that the observed changes in FcRn α and β 2 microglobulin gene expression in the proximal intestine are not modulated directly by prolactin. The results are consistent with the hypothesis that changes in FcRn α and β 2 microglobulin gene expression take place in the possum PY intestine to accommodate changes in maternal milk composition to meet the changing immunological demands of the PY.