|Cod Gadus morhua
|Almeida FF, Kristoffersen C, Taranger GL, Schulz RW. Spermatogenesis in Atlantic cod (Gadus morhua): a novel model of cystic germ cell development. Biol Reprod. 2008 Jan78(1):27-34PubMed ID17881768
|To estimate the number of pachytene spermatocytes per cyst, and thereby to conclude how many mitotic divisions the spermatogonia completed before entering meiosis, it was necessary to determine the average volume of spermatogenic cysts containing pachytene spermatocytes and the average volume of a pachytene spermatocyte. The volume of pachytene spermatocytes was calculated from the nuclear volume and the proportion between nucleus and cytoplasm. To assess the volume of the nucleus, its diameter was measured (30 pachytene spermatocytes per animal n=5). Since the pachytene nucleus is round, its volume was estimated using the formula (4/3)pR^3 (R=diameter/2), expressed in µm^3. To calculate the proportion between nucleus and cytoplasm, a grid with 121 intersections was placed over the sectioned material at 400× magnification. For each animal, 1000 points over pachytene spermatocytes were counted.
|The average volume of a pachytene spermatocyte was 70±6µm^3 per cell. Analyzing the volume of a total of 37 pachytene
spermatocyte cysts, researchers found that two thirds of the cysts
showed a volume indicating that the spermatogonia went
through 11 mitotic cell cycles, whereas the volume of the
remaining one third indicated that 12 mitotic cell cycles were
completed. These data resulted in an average volume of
pachytene spermatocyte cysts of 136±25 mm^3, suggesting
that approximately 1900 pachytene spermatocytes were present
per cyst. They therefore conclude that at least 11 mitotic cell
cycles are completed before entering meiosis (n.b. 2^11=2048).