The effects of collapsing factors on F-actin content and microtubule distribution ofHelisomagrowth cones

Abstract

Growth cone collapsing factors induce growth cone collapse or repulsive growth cone turning by interacting with membrane receptors that induce alterations in the growth cone cytoskeleton. A common change induced by collapsing factors in the cytoskeleton of the peripheral domain, the thin lamellopodial area of growth cones, is a decline in the number of radially aligned F-actin bundles that form the core of filopodia. The present study examined whether ML-7, a myosin light chain kinase inhibitor, serotonin, a neurotransmitter and TPA, an activator of protein kinase C, which induce growth cone collapse of Helisoma growth cones, depolymerized or debundled F-actin. We report that these collapsing factors had different effects. ML-7 induced F-actin reorganization consistent with debundling whereas serotonin and TPA predominately depolymerized and possibly debundled F-actin. Additionally, these collapsing factors induced the formation of a dense actin-ring around the central domain, the thicker proximal area of growth cones [Zhou and Cohan, 2001: J. Cell Biol. 153:1071-1083]. The formation of the actin-ring occurred subsequent to the loss of actin bundles. The ML-7-induced actin-ring was found to inhibit microtubule extension into the P-domain. Thus, ML-7, serotonin, and TPA induce growth cone collapse associated with a decline in radially aligned F-actin bundles through at least two mechanisms involving debundling of actin filaments and/or actin depolymerization.

P-Rex1 – a multidomain protein that regulates neurite differentiation

“…8B). The ratio of fluorescence of growth cone F-actin to G-actin was determined (Torreano et al, 2005). The growth cones of PRex1 RNAi neurites appeared smaller than those of scrambled RNAi neurites, with decreased F-actin relative to G-actin (Fig.…”

“…The ratio of F-actin to G-actin within the growth cone was determined as described (Torreano et al, 2005). Briefly, following 3-day NGF differentiation and fixation/permeabilisation as described above, cells were incubated with 18 μg/ml Alexa Fluor 594-conjugated DNaseI to visualise G-actin and 6.6 nM Alexa Fluor 488-conjugated phalloidin for F-actin.…”

Integrative biology of an embryonic respiratory behaviour in pond snails:the `embryo stir-bar hypothesis'

“…L. stagnalis has been used primarily to study the neural mechanisms underlying feeding and respiratory behaviours (Vavoulis et al, 2007;Bell et al, 2007;Haque et al, 2006), as well as a variety of questions on learning and memory (Martens et al, 2007), neural plasticity and cell biology (Dunn and Syed, 2006;Jimenez et al, 2006). While H. trivolvis has also contributed in some of these areas (Murphy, 2001;Torreano et al, 2005), it has become a particularly good model to address a broad range of developmental questions because of the advantageous morphological and biomechanical properties of its egg mass. The egg mass is a flat circular structure containing 5 to 50 sibling embryos, each housed individually in an egg capsule ( Fig.…”

A Trophic Role for Serotonin in the Development of a Simple Feeding Circuit

“…Later studies demonstrated that 5-HT induced a calcium influx-dependent inward sodium current via the actions of cyclic-nucleotide-gated channels [reviewed in Goldberg, 1998]. 5-HT has been shown to induce growth cone collapse and inhibit neurite outgrowth in Helisoma by depolymerizing F-actin, a critical cytoskeletal component of growth cones [Torreano et al, 2005]. While these studies demonstrated localized actions of 5-HT directly on growth cone activity in isolated neurons, further studies have shown that 5-HT can have more widespread effects on developing neuronal populations [Goldberg, 1998].…”