- A Kinesin, InvA, Plays an Essential Role in Volvox Morphogenesis
Cell, Volume 113, Issue 6, 13 June 2003, Pages 743-753
Ichiro Nishii, Satoshi Ogihara and David L. Kirk
SummaryIn Volvox carteri adults, reproductive cells called gonidia are enclosed within a spherical monolayer of biflagellate somatic cells. Embryos must “invert” (turn inside out) to achieve this configuration, however, because at the end of cleavage the gonidia are on the outside and the flagellar ends of all somatic cells point inward. Generation of a bend region adequate to turn the embryo inside out involves a dramatic change in cell shape, plus cell movements. Here, we cloned a gene called invA that is essential for inversion and found that it codes for a kinesin localized in the cytoplasmic bridges that link all cells to their neighbors. In invA null mutants, cells change shape normally, but are unable to move relative to the cytoplasmic bridges. A normal bend region cannot be formed and inversion stops. We conclude that the InvA kinesin provides the motile force that normally drives inversion to completion.
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- The highly efficient sex-inducing pheromone system of Volvox
Trends in Microbiology, Volume 6, Issue 5, 1 May 1998, Pages 185-189
Armin Hallmann, Klaus Godl, Stephan Wenzl and Manfred Sumper
AbstractThe green alga Volvox is one of the simplest multicellular organisms and is capable of both asexual and sexual reproduction. Sexual development is initiated by a glycoprotein pheromone that acts at a concentration below 10−16m. The extracellular matrix (ECM) appears to play a key role in signal amplification: several ECM proteins contain a domain with homology to the sex-inducing pheromone.
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- Two Light-Activated Conductances in the Eye of the Green Alga Volvox carteri
Biophysical Journal, Volume 76, Issue 3, 1 March 1999, Pages 1668-1678
Franz-Josef Braun and Peter Hegemann
AbstractPhotoreceptor currents of the multicellular green alga Volvox carteri were analyzed using a dissolver mutant. The photocurrents are restricted to the eyespot region of somatic cells. Photocurrents are detectable from intact cells and excised eyes. The rhodopsin action spectrum suggests that the currents are induced by Volvox rhodopsin. Flash-induced photocurrents are a composition of a fast Ca2+-carried current (PF) and a slower current (PS), which is carried by H+. PF is a high-intensity response that appears with a delay of less than 50μs after flash. The stimulus-response curve of its initial rise is fit by a single exponential and parallels the rhodopsin bleaching. These two observations suggest that the responsible channel is closely connected to the rhodopsin, both forming a tight complex. At low flash energies PS is dominating. The current delay increases up to 10ms, and the PS amplitude saturates when only a few percent of the rhodopsin is bleached. The data are in favor of a second signaling system, which includes a signal transducer mediating between rhodopsin and the channel. We present a model of how different modes of signal transduction are accomplished in this alga under different light conditions.