Colostrogenesis: candidate genes for I g G 1 transcytosis mechanisms in primary bovine mammary epithelial cells

Summary Bovine colostrogenesis is distinguished by the specific transfer of I g G 1 from the blood to mammary secretions. The process has been shown to be initiated by hormones and occurs during the last weeks of pregnancy when steroid concentrations of estradiol ( E 2 ) and progesterone ( P 4 ) are highly elevated. Rodent intestinal uptake of immunoglobulin G is mediated by a receptor termed F c fragment of I g G , R eceptor, T ransporter, alpha ( F c GRT ) and supported by light chain B eta‐2‐ M icroglobulin (β2 M ). We hypothesized that steroid hormone treatments ( E 2 and P 4 ) of bovine mammary epithelial cells in vitro would induce up‐regulation of I g G 1 transcytosis candidate gene m RNA expression suggesting involvement in I g G 1 transcytosis. Two different primary bovine mammary epithelial cell cultures were cultured on plastic and rat tail collagen and treated with hormonal combinations (steroids/lactogenic hormones). Evaluated m RNA components were b L actoferrin (b L f: a control), b F c GRT , β2 M , and various small GTP ases; the latter components are reported to direct endosomal movements in eukaryotic cells. All tested transcytosis components showed strong expression of m RNA in the cells. Expression of b F c GRT , b R ab25 and b R ho B were significantly up‐regulated (p < 0.05) by steroid hormones. b R ab25 and b R ho B showed increased expression by steroid treatments, but also with lactogenic hormones. Analysis for the oestrogen receptor ( ER ) m RNA was mostly negative, but 25% of the cultures tested exhibited weak expression, while the progesterone receptor ( PR ) m RNA was always detected. b R ab25 and b R hoB and likely b F c GRT are potential candidate genes for I g G 1 transcytosis in bovine mammary cells.