The expression and localisation of connexins during different functional stages in the bovine corpus luteum

Connexins (cx) are structure proteins of gap junctions that seem to play an important role during ovarian function in mammals. The aim of this study was to characterise the mRNA expression and protein localisation of connexins (cx26, cx32 and cx43) during different stages of the oestrous cycle in bovine corpus luteum (CL). Corpora lutea were assigned to the following stages; Days 1–2, 3–4, 5–7, 8–12, 13–17, >18 (after regression) of oestrous cycle and of early and late pregnancy (<4 and >4 month). For the experimental luteolysis, cows on days 8–12 were injected with PGF2alpha analogue (Cloprostenol), and CL were collected by transvaginal ovariectomy before and at 0.5, 2, 4, 12, 24, 48 and 64h after PGF2alpha injection (n=5–6). Real time RT-PCR (Rotor-Gene) was applied to investigate mRNA expression and immunofluorescence was utilised for protein localisation. The highest mRNA expression for cx43 was detected during the early luteal phase, followed by a significant decrease of expression during the mid and late luteal phase and after regression. During pregnancy, high levels of expression were always present. In contrast, no significant change in cx26 mRNA expression during the oestrous cycle and pregnancy was found. The CL tissue did not express cx32 mRNA. During induced luteolyses the mRNA expression of cx26 tended to increase after 12h and became significant 24h after PGF2alpha injection. In contrast, no significant change in cx43 mRNA expression during induced luteolyses was observed. As shown by immunofluorescence, cx26 and cx43 were predominantly localised in the connective tissue and blood vessels of bovine CL. However, a dramatic increase of cx26 expression occurred during late luteal phase and after luteal regression. In contrast, cx43 expression was distinctly decreased after luteal regression in cow. These data suggest, that connexins are involved in the local mechanisms regulating tissue remodelling during corpus luteum function and corpus luteum regression in the bovine ovary.

Supported by DFG (BE 3189/1–3).