Parthenogenesis in Urechis caupo (Echiura). II. Role of intracellular pH in parthenogenesis induction.
A peptide (P23) isolated from sperm acrosomal protein initiates development in eggs of the marine worm Urechis caupo. We have shown previously that eggs exposed to P23 for > or = 3 min complete meiosis but fail to cleave. However, a brief (1.5-2 min) exposure to P23 at pH 8, followed by either acidification of the seawater of pH 7 or dilution of P23 at pH 8 causes germinal vesicle breakdown (GVBD), but eggs fail to complete meiosis and many then later advance to mitosis. In the present study we investigated the hypothesis that partial activation leading to parthenogenesis occurs when there is a partial intracellular alkalinization. Measurements with the fluorescent pH indicator bis(carboxyethyl)-carboxyfluorescein (BCECF) showed that P23 induces a pHi increase similar to that occurring during fertilization and the parthenogenesis-inducing treatments interrupt this rise in pHi. In eggs exposed to P23 for > 3 min the pHi increase was 0.31-0.49 units, slightly higher than in fertilized eggs. In partially activated eggs exposed to P23 for 1.5-2 min at pH 8, pHi began to rise but then returned to control values or remained only partially elevated (< 0.2 pH units average increase). Electrophysiological measurements revealed that removal of P23 during the first few minutes of exposure caused the activation potential to terminate and experiments with [14C]-P23 confirmed that dilution results in a rapid unbinding of P23 from eggs. If proton export is driven by membrane potential as well as the pH gradient, these results explain why dilution of P23 at pH 8 also interrupts the pHi increase.
Stephano
J L
JL
Facultad de Ciencias, Universidad Autónoma de Baja California, Ensenada, México.
Gould
M C
MC
D000818:Animals; D000845:Annelida / Q000502:physiology*; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D036341:Intercellular Signaling Peptides and Proteins; D007424:Intracellular Fluid / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D010063:Ovum / Q000187:drug effects / Q000502:physiology; D010312:Parthenogenesis / Q000187:drug effects / Q000502:physiology*; D010455:Peptides / Q000302:isolation & purification / Q000494:pharmacology / Q000502:physiology; D013094:Spermatozoa / Q000737:chemistry / Q000502:physiology
D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; C070205:sperm acrosomal peptide P23