Expression of oestrogen receptor alpha during development of the skeleton in mice fetuses: immunohistochemical study

Sequential pattern of ossification and expression of oestrogen receptor alpha (ERalpha) during development of the skeleton in male and female mice fetuses was investigated. Twenty-seven mice fetuses of gestational age between 14.5 and 18.5 days post coitum (p.c.) were examined by haematoxylin-eosin and toluidine blue staining to determine the ossification. The presence of ERalpha was detected by immunostaining using ERalpha-specific antibodies. Ossification centres were determined in fetuses of 14.5 days p.c. of both sexes in the base of skull, ribs and front limbs, while in the mandible ossification was observed only in female fetuses at that age. ERalpha was found in all investigated tissues in which the occurrence of ossification centres was determined. ERalpha was first detected in some tissues involved in ossification at 14.5 days p.c. in fetuses of both genders. There were some minor gender differences in the pattern of ERalpha expression. ERalpha was localized in the metatarsal chondrogenic condensations at 14.5 days p.c. and in phalangeal chondrocytes at 17.5 and 18.5 days p.c. only in females. ERalpha-positive osteogenic cells at 14.5 days p.c. in the mandible were seen only in females. At 16.5 days p.c. male but not female fetuses expressed ERalpha in the vertebrae. Our findings support the view that ERalpha protein is found in the tissues that undergo bone formation and that ERalpha expression in these tissues shows only minor gender differences in mice fetuses.