Autonomous regulation of growth cone filopodia

Filopodial behavior is dependent on the phosphorylation state of neuronal growth cones

“…Immediately before the experiment, each drug was premixed in 2 ml of L-15 medium to its final concentration and introduced into the dish by a full medium exchange. The medium change was performed by removing all medium, except from the center well as described previously [Rehder and Cheng, 1998]. Controls included a medium change with defined medium (L-15) and addition of DMSO (0.4% final concentration) or 50% ETOH (0.1% final concentration).…”

“…Growth cones were viewed through a 100ϫ oilimmersion objective on an Axiovert 135 (Carl Zeiss, Thornwood, NY) or a Sedival (aus Jena, Germany) inverted microscope, and phase images and calcium measurements were obtained as described previously [Rehder and Cheng, 1998]. In short, 6 -10 growth cones were randomly selected in each dish and two control images were obtained at five min (t ϭ Ϫ5) and immediately before treatment (t ϭ 0).…”

“…For calcium imaging, somata were injected with Fura-2 pentapotassium salt (10 mM in water; Molecular Probes, Eugene, OR) and used 30 min after injection. Fura-2 was excited at two different excitation wavelengths (340 Ϯ 10 nm and 380 Ϯ 10 nm) and the fluorescence emission was filtered with a 495-nm-long pass emission filter as previously described [Rehder and Cheng, 1998]. The ratio (R) of the fluorescence intensity of the two images at 340 and 380 nm was plotted against time to indicate changes in [Ca 2ϩ ] i .…”

Models for spatial polymerization dynamics of rod-like polymers

“…In growing one-dimensional protrusions such as spikes, microvilli, stereocilia, and "lopodia, the forward motion of the cytoskeleton in response to certain stimuli (e.g. Rehder and Cheng, 1998), or during developmental processes (Tilney and DeRosier, 1986;Tilney et al, 1991) implies that actin polymerization is taking place in a spatially controlled way. Similarly, intracellular parasites such as¸ysteria monocytogenes see (Marchand et al, 1995), exploit actin polymerization to move through the cell.…”

“…Typical one-dimensional structures that contain actin "laments are cylindrical in shape with roughly the following dimensions: for stereocilia, which are appendages on hair cells in the auditory system, the diameter is 0.1!0.2 and the length is 1!5 (Tilney and DeRosier, 1986). For "lopodia in neural growth cones, typical lengths are 10!25 (Rehder and Cheng 1998). For the acrosomal process of the sea cucumber, ¹hyone, the diameter is roughly 0.05 and the length is up to 90 (Oster and Perelson, 1987).…”