THE PATTERN OF CELL-PROLIFERATION DURING PEARL SAC FORMATION IN THE PEARL OYSTER

For cultured pearl production, a mantle allograft from a donor is impl anted into a recipient gonad together with a small inorganic bead. Enc apsulation of the grafts by hemocytes follows. The mantle allograft's outer epithelial cells subsequently emigrate along the inside of the h emocyte capsule, and eventually form a follicle, called a pearl sac, s urrounding the bead. To clarify the cell types involved and timing of mitotic activity in the process of pearl sac formation, pearl oysters at various phases of pearl sac formation were injected with a thymidin e analog, 5-bromo-2'-deoxyuridine (BrdU), and dividing cells labeled w ith BrdU were visualized with anti-BrdU antibody. At 4 days after impl antation, the epidermal cells (dominant cells in the outer epithelium) of the allograft initiated active proliferation and emigration. Their mitoses continued during emigration and after establishment of the pe arl sac. No incorporation of BrdU into the other two types of mantle e pithelial cells (mature mucous cells and cells with large granules) wa s observed. In the gonad surrounding the pearl sac, a large number of connective tissue cells among gonadal follicles and around the intesti ne showed peak mitotic activity around one week after the operation, w hich implied activation of hemocyte production.