title: The contractility of elongated microvilli in early sea urchin embryos.
abstract: Elongated microvilli attach the early sea urchin embryo to the fertilization envelope and support it in a concentric position within the perivitelline space. The contractility of the elongated microvilli was demonstrated in several ways. (1) During normal cleavage, these microvilli change their length to adapt to the change in shape and numbers of blastomeres. (2) When treated with calcium-free sea water, embryos become eccentrically located and the microvilli extend further than normal on one side; when returned to normal sea water, the embryos become centered again. (3) Several agents cause the fertilization envelope to become higher and thinner than normal and the elongated microvilli to extend correspondingly if treated within ten min after fertilization. In some cases, both elongated microvilli and fertilization envelope return to normal size when returned to normal sea water. (4) Fertilization in a papain solution causes the elongated microvilli and the fertilization envelope to contract to the surface of the embryo. (5) Refertilization after the papain-induced contraction can bring about the elongation of these microvilli and the elevation of the fertilization envelope a second time. It was also shown that elongated microvilli are extended immediately upon fertilization, at the same time as the short microvilli. The firm adherence of the tips of elongated microvilli to the fertilization envelope by means of extracellular matrix fibers is shown in a high voltage electron microscope stereoimage. This allows us to understand why it is that when the elongated microvilli extend or contract, the fertilization envelope also extends and contracts accordingly.
authors.affiliation: Department of Biological Sciences, Dartmouth College, 03755, Hanover, NH, USA.|Marine Biological Laboratory, Woods Hole, 02543, MA, USA.
authors.forename: Evelyn
authors.initials: E
authors.lastname: Spiegel
authors.affiliation: Department of Biological Sciences, Dartmouth College, 03755, Hanover, NH, USA.|Marine Biological Laboratory, Woods Hole, 02543, MA, USA.
authors.forename: Louisa
authors.initials: L
authors.lastname: Howard
authors.affiliation: Department of Biological Sciences, Dartmouth College, 03755, Hanover, NH, USA.|Marine Biological Laboratory, Woods Hole, 02543, MA, USA.
authors.forename: Melvin
authors.initials: M
authors.lastname: Spiegel
keywords: Contractility; Elongated microvilli; Extracelluar matrix; Fertilization envelope; Sea urchin embryo