Expression of prostaglandin synthesizing enzymes (cyclooxygenase 1 and cyclooxygenase 2) in the ovary of the ostrich (Struthio camelus)

Cyclooxygenase is the rate limiting enzyme in the production of prostaglandins. In birds two isoforms are present: cyclooxygenase 1 (COX-1) and cyclooxygenase 2 (COX-2). Despite evidence implicating that cyclooxygenases and PGs are critical factors in female reproduction in birds, little is known about COX expression in the avian ovary. In birds, cyclooxygenases have been studied in very few species only. In this study we report on the expression of COX-1 and COX-2 in the ovary of the ostrich (Struthio camelus) using immunohistochemistry and non-radioactive in situ hybridization techniques. Our results demonstrate that COX-1 is strongly expressed in the cytoplasm of oocytes of previtellogenic follicles, whereas COX-2 shows the strongest immunostaining in the granulosa cells of previtellogenic follicles. The signals of both isoenzymes fade significantly with increasing diameter and finally nearly vanish in the vitellogenic follicles with a size >1.8cm. This expression pattern in the ostrich (S. camelus) is, therefore, completely different from the localization of COX-1 and COX-2 in the hen (Gallus gallus), a finding which also suggests different functions of the cyclooxygenases in the ostrich species. Non-radioactive in situ hybridization confirmed that COX-1 is synthesized in the ooplasm and COX-2 in the granulosa layers of early previtellogenic follicles. According to the results of this study it appears unlikely that COX-1 or COX-2 play a major role in ovulation and oviposition in the ostrich.