title: Blastopore formation in the animal hemisphere: functional inversion of gastrulation by centrifugation of Xenopus laevis eggs.
abstract: Eggs of Xenopus laevis and many other amphibians contain a gradient of yolk platelets along the animal-vegetal axis. Small platelets predominate in the animal hemisphere, and a boundary between medium and large yolk platelets exists near the equator. The blastopore forms at this boundary at the beginning of gastrulation, in the vegetal hemisphere. Does this boundary have a role in determination of the position of the blastopore, or does cortical information predominate? Past experiments using 1g to invert the egg showed a distinct tendency to form the blastopore in the original vegetal hemisphere. Our experiments, however, have used 20g centrifugation to achieve a more complete inversion of the yolk gradient. The blastopore formed in the original animal hemisphere in >95% of surviving gastrulae, if centrifugation was begun at normalized time 0.20-0.25 of the first cell cycle. Nearly normal larvae (DAI grades 4 and 5) form in 64% of cases (ave. DAI = 3.2). These data support the idea that the position of the blastopore depends on the position of the egg's internal contents rather than cortical determinants.
authors.affiliation: Department of Biology, Reed College, Portland, Oregon, USA.
authors.forename: S D
authors.initials: SD
authors.lastname: Black
authors.forename: A N
authors.initials: AN
authors.lastname: Crutchfield
authors.forename: M D
authors.initials: MD
authors.lastname: Murphy
authors.forename: T C
authors.initials: TC
authors.lastname: Swain
mesh_terms: D000818:Animals; D019521:Body Patterning / Q000502:physiology*; D016764:Cell Polarity; D002498:Centrifugation; D015509:Developmental Biology; D004625:Embryo, Nonmammalian / Q000502:physiology; D005260:Female; D005775:Gastrula / Q000166:cytology / Q000502:physiology*; D018471:Hypergravity; D008297:Male; D010063:Ovum / Q000502:physiology*; D013084:Sperm-Ovum Interactions; D014982:Xenopus laevis / Q000196:embryology*