Effects of cytochalasin B on fertilization and ploidy in the Pacific oysterCrassostrea gigas

Abstract

The effects of cytochalasin B on fertilization and ploidy in Crassostrea gigas were examined in a controlled experiment. This enabled us to better understand why variable ploidy results have been found with the retention ofpolar bodies in previous studies on bivalve mollusks, and what the interaction with fertilization may be. By looking at the early development of Crassas/rea gigas embryos with sequential sampies stained using Hoechst 33258, a fluorescent DNA-specific dye, we compared normal evolution of fertilized eggs with that obtained with cytochalasin B treatrnent. In treated eggs, embryos with both three and four pronuclei were found after the second meiotic division. When embryos had three pronuclei, these were identified as the female pronucleus plus two chromatin groups arising from the retention of the two polar bodies. The fourth pronucleus present in sorne embryos was the male pronucleus. The absence of the male pronucleus in the embryos with only three pronuc1ei was interpreted as gynogenetic development due to the inhibitory effects of cytochalasin B on penetration of the sperm into the eggs. This result explains the findings of several previous studies where different ploidies resulted from double polar body inh ibition in bivalve species. Implications ofsuch treatments for post-embryo genic development are discussed.

A Complementary Method for Production of Tetraploid Crassostrea gigas Using Crosses Between Diploids and Tetraploids with Cytochalasin B Treatments

“…Nonpenetration may be a side effect of CB (Longo, 1978;Ledu and McCombie, 2003). We have also observed unusual patterns of PB expulsion in other ploidy manipulation experiments; on rare occasions these included the expulsion of most or all the genetic material in one PB (Ledu and McCombie, 2003). The effects of CB may therefore be diverse.…”

“…The objective was to determine whether or not the paternal parents had participated in the cross, first because our initial ploidy results had revealed diploids in batch 3, and it is known that diploid gynogens may be produced by CB treatments in this species (Guo et al, 1993). Second, results from our embryogenesis study had also indicated some double polar body retention, which could lead to tetraploid gynogens (Guo et al, 1993;Ledu and McCombie, 2003).…”

Short sharp shock produces viable tetraploids in crosses of diploid blue musselsMytilus edulis

“…This principal has formed the basis of ploidy manipulation in many aquatic organisms with external meiosis. Results in oyster embryos also indicate a role of CB in the sperm–egg relationship that can lead to tetraploidy through gynogenesis (Ledu & McCombie 2003). The present study therefore used early treatments to potentially exploit this mechanism.…”

“…Guo & Allen 1994). If there was no paternal contribution, then the gynogenetic hypothesis of Ledu and McCombie (2003) would be confirmed.…”

Comparative study on tetraploid induction of the Fujian oyster Crassostrea angulata utilizing three typical methods

“…The survival rate of larvae under all three methods in this study decreased signi during the rst 10 days under all three methods. could be rstly due to the very high toxicity of the inducer, which severely deteriorated the larval survival rate (Ledu and McCombie 2003;Yang et al 2000; Peachey and Allen 2016). Additionally, blocking PB1 has been known to induce aberrations in chromosome segregation, such as tripolar segregation and heterogeneous chromosome distribution, causing massive aneuploidy and reduced viability (Guo et al 1992a).…”