title: Absence of furrowing activity following regional cortical tension reduction in sand dollar blastomere and fertilized egg fragment surfaces.
abstract: The purpose of the present investigation was to test experimentally the possibility that division mechanism establishment at the equator of sand dollar eggs may be a consequence of cortical tension gradients between the equator and the poles. Cytochalasin has been shown to decrease tension at the sea urchin egg surface. The concave ends of cytochalasin D-containing agarose cylinders were held against regions of the surface of Echinarachnius parma blastomeres and enucleated fertilized egg fragments. The ability to interfere with normal furrowing activity was used as a biological indicator of the effectiveness of cytochalasin. When agarose containing 2 microg/mL cytochalasin contacted the equatorial region of the blastomeres resulting from the first cleavage, or the equatorial surfaces of nucleated fertilized egg halves, furrowing was blocked, stalled or delayed, indicating that the concentration of cytochalasin was effective. When the same concentration of cytochalasin was applied to the poles, the cells and nucleated fertilized egg fragments divided in the same way as the controls, indicating that the effectiveness of the cytochalasin did not spread from the poles to the equator and that bisection did not interfere with the division of nucleated fertilized egg fragments. When the same concentration of cytochalasin was applied to diametrically opposed surfaces of enucleated, spherical egg fragments, there was no evidence of furrowing activity between the areas that contacted the cytochalasin or in any other part of the surface. Because of the tension-reducing effect of cytochalasin, a tension gradient existed between the regions affected and unaffected by cytochalasin. The results strongly suggest that establishment of the division mechanism by simple gradients of tension at the surface is unlikely.
authors.affiliation: The Mount Desert Island Biological Laboratory, Salsbury Cove, ME 04672, USA. brappaport@acadia.net
authors.forename: R
authors.initials: R
authors.lastname: Rappaport
mesh_terms: D000818:Animals; D001757:Blastomeres / Q000166:cytology*; D002455:Cell Division / Q000502:physiology*; D016764:Cell Polarity / Q000502:physiology*; D003572:Cytochalasins / Q000494:pharmacology*; D008845:Microinjections; D010063:Ovum; D012617:Sea Urchins / Q000166:cytology / Q000196:embryology* / Q000254:growth & development; D013500:Surface Tension
chemical_list: D003572:Cytochalasins