Localization of the Nucleus During Early Avian Follicular Development
Long term surveys demonstrate a decline in avian populations in North American ecosystems. A better understanding of avian reproductive functions, using the domestic chicken as a model organism, would help strengthen breeding programs. The germinal disc (GD) is a structure that contains the nucleus and organelles of the oocyte in the ovarian follicle. The importance of the GD in maintaining viable ovarian follicles and influencing granulosa cell proliferation and responsiveness to hormones has been established in pre-ovulatory follicles. However, the role of the GD during early ovarian follicular development is currently unknown due to the follicle’s significantly smaller size. The purpose of this project was to determine the position of the GD relative to the perivitelline membrane of follicles ranging from smaller than 50µm to greater than 500µm. The ovaries of two White Leghorn hens were harvested and fixed using 10% neutral buffered formalin and processed for paraffin-embedding. Microtome sections were cut at 5µm and stained using hematoxylin and eosin (H&E) stains. The ratios between the shortest distance and the longest distance of the GD relative to the perivitelline membrane were measured using Olympus cellSens software within six size categories: follicles smaller than 50µm, 50-100µm, 100-200µm, 200-300µm, 300-500µm and greater than 500µm. The values were averaged between the ovaries for comparison. A value closer to 0 indicates the GD was located in the periphery, closer to the perivitelline membrane, of the follicle while a value closer to 1 indicates the GD was located in the center of the follicle. The smallest ratio values were observed in follicles within the first two size categories, averaging 0.18 and 0.16, and increased as the next four size categories increased, averaging 0.29, 0.43, 0.56 and 0.52, suggesting movement of the GD from a peripheral to a more central location within the follicle. We are currently working on increasing the number of hens sampled. Future studies will focus on extracting the GD to analyze factors secreted at each stage and their influence on granulosa cells to better understand the role of the oocyte in driving early follicular development in avian species, with potential applications of ovarian follicle preservation and reestablishing endangered avian populations.