BrdU labelling of oocyte in the rat fetus ovary

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INTRODUCTIONIn order to analyze the follicular development dynamically, it is effective to set up a cohort by labelling a part of follicles and to follow up their growth. It is widely known that rat's oocyte doubles its DNA in the embryonal stage and its mitosis has been arrested until the second meiosis just before ovulation. We noticed this phenomenon is available to determine the possibility of labelling a certain group of oocyte's nuclei in the embryonal stage.MATERIALS AND METHODSThe pregnant rats were divided into four groups (A, B, C and D group, each consisted of 4 animals) and transabdominally injected with bromodeoxyuridine (BrdU) 5 g/body weight (g) at one time in the 17th day of pregnancy. They were reared to delivery. Thereafter, the female newborn animals were reared and sacrificed at 1week (group A), 2week (B), 3week (C) and 4week (D) to excise bilateral ovaries and liver. These organs were fixed in formalin, embedded in paraffin, and then serially sliced at 5 m in thick … More ness. Every seventh section was mounted on slide glass. Immunohistochemical staining was employed with anti-BrdU monoclonal antibody (Boehringer-Mannheim Biochemica) by using Biotin-streptAvidin's method. We investigated the localization of BrdU which was incorporated into the cell.RESULTS AND DISCUSSION1) A part of fetal oocytes were labelled by BrdU in the 17th day of pregnancy and their labelling in the nuclei were maintained up to 4th week after delivery (group A, B, C, D). On the contrary, liver cells showed positive staining of BrdU in group A, however, BrdU labelling was not detectable in group B, C, and D. Therefore, it was clarified that BrdU-uptake in the liver cell was so diluted at its every mitosis to the degree which could not be demonstrated.2) BrdU labelling was evident mainly in the primordial follicle which did not have granulosa cells. At 1 week of delivery (group A), the follicles labelled by BrdU were 100% of the primordial follicles. The primordial follicles occupied 96.3% of the tagged follicles at 2 week of delivery (group B) and 46.7% at 3 week (group C). This decreased incidence of BrdU-labelled primordial follicles presented that some follicles in given BrdU-labelled cohort were developed into the next category of primary follicles accompanied with a few layers of granulosa cells. However, there were only 1 or 2 vesicular follicles showing BrdU incorporation through 1 to 4 week of delivery. Less