The temporal and spatial relationships between cortical contraction, sperm trail formation, and pronuclear migration in fertilizedXenopus eggs

Abstract

The cortical contraction begins 4 min after insemination and one minute after prick activation. During the next 4 min, the pigment margin moves 15 degrees toward the animal pole. The cortex then relaxes to the prefertilization level over the next 10 min. Contrary to earlier estimations, the cortical contraction occurs during the same time span as the wave of cortical granule exocytosis. We suggest that the two events may result from a common stimulus. The sperm trail (ST) forms during the relaxation of the cortex. The ST first appears as a conically-shaped trail of pigment in the cytoplasm; it then elongates into a funnel-shaped trail as the male pronucleus migrates into the egg. The base of the cytoplasmic ST can be seen on the surface of the egg as a circular condensation of pigment. The male and female pronuclei migrate at a constant rate of 12 μm per minute. The male pronucleus migrates by the enlargement of its aster, whereas, it appears that the female pronucleus is dependent on the male aster for its motion.

Establishment of polarities in the oocyte of Xenopus laevis: the provisional axial symmetry of the full-grown oocyte of Xenopus laevis

“…Pigment concentrates about the SEP, marking the future ventral side, and making axis manipulation possible in early stages [10,13,58,59,107]. The path of the migrating male pronucleus (plate I, A) is marked by pigment granules, drawn into the cytoplasm from the egg surface as the sperm moves inward (NT 0.17-0.61) [6][7][8][9][10]13]. The female pronucleus moves down from the animal pole, probably soon coming under influence of the spermaster [108].…”

“…As a consequence the two animal-dorsal blastomeres are smaller in most 8-cell Xenopus embryos [26]. During the first cell cycle two main independent microtubular entities develop: (1) the spermaster, initiated in the animal hemisphere by the sperm centriole [6,7,9], and (2) an array of parallel MT in the subcortical cytoplasm of the vegetal hemisphere about half-way through the first cleavage [82a, 107, 110]. In 6 mm paraffin sections of Bouin d'Hollande-fixed [77, 85, 86, 96a] Xenopus eggs we analyzed the three-dimensional distribution of tubulin with a modified peroxidase-anti-peroxidase (PAP) procedure [82, 82a].…”

“…The constant growth rate of the spermaster microtubules causes the male and female pronuclei to migrate at a constant rate of 12 mm per min [6,9,107,111]. While the animal cortex locally contracts on the SEP side, the astral rays reach the opposite side at NT 0.65 -0.8.…”

Spatiotemporal lipid profiling during early embryo development of Xenopus laevis using dynamic ToF-SIMS imaging

“…For X. laevis , studies have indicated a signifi cantly higher number of spermatozoa binding to the animal hemisphere ( 35,36 ). The fi rst visible sign of egg activation is the movement of pigment granules toward the animal pole (termed cortical contraction), which occurs approximately 4 min after fertilization ( 37 ). Our aim was to investigate the biological phenomenon on the surface of the egg shortly after the fertilization.…”

3 Actin and Actin-Associated Proteins in Xenopus Eggs and Early Embryos: Contribution to Cytoarchitecture and Gastrulation

“…During fertilization of most species, the sperm entry into the egg cytoplasm, the exocytosis of cortical granules, and the meeting of sperm and egg pronuclei all appear to require actin filaments (Stewart-Savage and Grey, 1982;reviewed in Vaquier, 1981).…”