A Temperature-Dependent Index of Mitotic Interval (τ₀) for Chromosome Manipulation in Paddlefish and Shovelnose Sturgeon

Abstract

A temperature-dependent measure of the mitotic interval (τ₀) can help standardize chromosome manipulation in fish eggs. A tau unit (τ₀) is the duration in minutes of one mitotic cycle during synchronous embryonic cleavage. It is measured over a range of temperatures, and the resulting relationship of τ₀ to temperature can be used to anticipiate developmental events that are affected by temperature. Optimum induction of chromosome manipulation requires development of a specific treatment of egg shocking for each species, Timing of shock is a critical variable, but pretreatment incubation temperature affects the rate of development and thus the optimum absolute time for shocking. Mitotic intervals (τ₀) are reliable indicators of developmental rates over normal temperatures for egg incubation, and thus can be used to estimate optimal times for chromosome manipulation, Mitotic intervals for paddlefish Polyodon spathula and shovelnose sturgeon Scaphirhynchus platorynchus were estimated by averaging the duration of the second and third embryonic divisions (twocell to four-cell and four-cell to eight-cell stages). Mitotic intervals (τ₀) for paddlefish ranged from 74 ± 2.8 min (mean ± SD) at 16°C to 52 ± 1,4 min at 20°C; τ₀ for shovelnose sturgeon was 66 ± 2,5 min and 45 ± 1,1 min at these temperatures.