Microinjection of antibodies in the analysis of cellular architecture and motility

Minimal impact electro-injection of cells undergoing dynamic shape change reveals calpain activation

The ability of neutrophils to rapidly change shape underlies their physiological functions of phagocytosis and spreading. A major problem in establishing the mechanism is that conventional microinjection of substances and indicators interferes with this dynamic cell behaviour. Here we show that electroinjection, a "no-touch" point-and-shoot means of introducing material into the cell, is sufficiently gentle to allow neutrophils to be injected whilst undergoing chemokinesis and spreading without disturbing cell shape change behaviour. Using this approach, a fluorogenic calpain-1 selective peptide substrate was introduced into the cytosol of individual neutrophils undergoing shape changes. These data showed that (i) physiologically elevated cytosolic Ca(2+) concentrations were sufficient to trigger calpain-1 activation, blockade of Ca(2+) influx preventing calpain activation and (ii) calpain-1 activity was elevated in spreading neutrophil. These findings provide the first direct demonstration of a physiological role for Ca(2+) elevation in calpain-1 activation and rapid cell spreading. Electroinjection of cells undergoing dynamic shape changes thus opens new avenues of investigation for defining the molecular mechanism underlying dynamic cell shape changes.

Microinjection of calpastatin inhibits fusion in myoblasts

Rat satellite cells (RSC) were microinjected with purified calpastatin or m-calpain, and myoblasts from a C2C12 mouse line were microinjected with purified calpastatin. Microinjection with calpastatin completely prevented fusion of myoblasts from both sources, whereas microinjection with m-calpain significantly increased the rate of fusion of cultured RSC; 44% of the nuclei of RSC cultures were in multinucleated myotubes within 48 h after microinjection with m-calpain plus labeled dextran, whereas only 15% of the nuclei were in multinucleated myotubes after microinjection with dextran alone. Western analyses indicated that neither RSC nor C2C12 myoblasts contained detectable amounts of mu-calpain before fusion. The levels of calpastatin in C2C12 myoblasts increased as cells passed from the proliferative stage to the onset of fusion, and these levels increased substantially in both the C2C12 and the RSC cells as they progressed to the late or postfusion stage. Both RSC and C2C12 myoblasts contained an 80-kDa polypeptide that was labeled with an anti-m-calpain antibody in Western blots. The results are consistent with a role of the calpain system (m-calpain in these myoblast lines) in remodeling of the cytoskeletal/plasma membrane interactions during cell fusion.

Microinjection of anti-alpha-tubulin antibody (DM1A) inhibits progesterone-induced meiotic maturation and deranges the microtubule array in follicle-enclosed oocytes of the frog, Rana pipiens

Microinjection of anti-alpha-tubulin (Dm1A) inhibited progesterone-induced meiotic maturation in large follicle-enclosed oocytes of the frog, Rana pipiens. DM1A (46 nl; 10 mg/ml) injection significantly increased the ED50 value for progesterone as determined by germinal vesicle dissolution (GVD) bioassay. By contrast, low doses of microinjected DM1A (46 nl; 2.5 mg/ml), anti-actin (clone KJ43A), anti-cytokeratin (C-11), anti-intermediate filament antibody (IFA), generic IgG (46 nl; 20 mg/ml) or sodium azide (46 nl; 1 mg/ml), an antibody preservative, were without inhibitory effect in this bioassay. Microinjected, affinity-purified DM1A (46 nl; 7.5 mg/ml) was also inhibitory, but preabsorption with pure tubulin prior to injection significantly reduced the inhibitory effect. DM1A injection had no effect on centrifugation-induced germinal vesicle migration (GVM). Previous work indicated that drugs (e.g. demecolcine and nocodazole), which destabilise microtubules, enhance both centrifugation-induced GVM and progesterone-induced GVD in Rana oocytes. Taking these results together, it is suggested that DM1A injection may have differential effects on microtubules in this cell. Thus, while the majority of microtubules were apparently depolymerised by DM1A (46 nl; 10 mg/ml) injection, a small subpopulation appeared to be stabilised as bundles. Confocal immunofluorescence microscopy of follicle-enclosed oocytes after DM1A injection revealed a major loss of microtubules throughout the cell; however, apparent sparse bundles of microtubules arranged in an approximately 600 microns shell were associated with the injectate region 24 h post-injection. By contrast, control follicle-enclosed oocytes topically labelled with DM1A post-fixation had extensive microtubule arrays similar to those previously reported in Xenopus oocytes. Intracellular recording after DM1A injection and progesterone treatment yielded an intermediate membrane potential (Vm = -31.8 mV) compared with control (immature) DM1A-injected cells (Vm = -44.7 mV) or potassium balanced salt solution (KBS)-injected cells matured with progesterone (Vm = -13.9 mV). These results suggest that DM1A injection does not completely inhibit electrophysiological changes initiated by progesterone. Working hypotheses are proposed that suggest a role for microtubules in the action of progesterone which normally lifts the prophase I block in the Rana follicle-enclosed oocyte.

Tyrosine-phosphorylated T cell receptor zeta chain associates with the actin cytoskeleton upon activation of mature T lymphocytes

The multichain T cell antigen receptor (TCR) is composed of an antigen binding (alpha/beta) domain and associated signal-transducing complexes, the CD3 (gamma, delta, and epsilon) and the zeta chains. The zeta chain (TCR zeta) plays a key role in signal transduction. We show here that TCR ligation induces association of tyrosine-phosphorylated TCR zeta with the detergent-insoluble cell fraction. The microfilament poison, cytochalasin D, disrupts this association and enhances the coprecipitation of actin with TCR zeta after receptor ligation. This microfilament association is specific to TCR-associated polypeptides containing at least one intact immunoreceptor tyrosine-based activation motif (ITAM). Mapping studies using transfectants and chimeric TCR zeta chain constructs suggest that the third ITAM is necessary and sufficient for association, if the distal tyrosine is intact. This cytoskeletal association is directly correlated with IL-2 production, and ligation of TCR on immature thymocytes does not induce TCR zeta-cytoskeleton association. These data thus provide direct evidence of a developmentally regulated activation-dependent interaction between a lymphocyte antigen receptor and the actin cytoskeleton.