P40 | VOLUME ELECTRON MICROSCOPY REVEALS SPECIFIC FEATURES OF MITOTIC CELLS IN THE PINEAL ORGAN OF THE DOMESTIC TURKEY

B. Lewczuk, N. Szyryńska, M. Prusik | Department of Histology and Embryology, Faculty of Veterinary Medicine, University of Warmia and Mazury in Olsztyn, Poland

The avian pineal organ originates as an evagination of the third ventricle. This evagination elongates to form the pineal canal, which often extends to the apical region of the pineal organ and remains connected to the third ventricle during embryonic and, in some cases, early postembryonic development. The pineal canal serves as the primary source of cells for the formation of parenchymal structures such as follicles and rosettes. In this study, we examined the 3D ultrastructure of the pineal canal in 18-dayold domestic turkey embryos to characterize mitotic cells. Imaging was performed using a 3View 2XP system (Gatan) integrated with an EF-SEM Gemini 450 (Carl Zeiss). Two cell types were identified: rudimentary receptor pinealocytes (RRP) and ependymal-like supporting cells (ELSC), both exhibiting polarized and highly organized cytoplasmic architecture. RRP formed single, elongated basal processes, which created prominent flattened segments that lay within invaginations of ELSC. Fine extensions of RRP occasionally reached the basement membrane. ELSC had broad basal portions resting on the basement membrane. Mitotic cells were located between RRP and ELSC and consistently maintained contact with the canal lumen. These cells exhibited numerous fine, long projections, resembling horse-tail hairs extending toward the basement membrane. In prophase, Golgi dictyosomes appeared small and dispersed, mitochondria were present on both apical and basal sides of the nucleus, and endoplasmic reticulum (ER) was localized mainly peripherally. During metaphase, ER was restricted to the cell periphery and mitochondria were sparse. In telophase and cytokinesis, the hair-like projections were asymmetrically distributed between daughter cells. The daughter cells were connected by a fine cytoplasmic bridge near the canal lumen, which disappeared as differentiation progressed. Our findings show that mitotic cells in the pineal canal share some morphological characteristics with those in the developing neural tube. Further research is required to clarify the differentiation of RRP and ELSC.
Supported by the Ministry of Science under the “Regional Initiative of Excellence” program.