Actin polymerization and synthesis in cultured neurones

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Sympathetic neurons cultured with nerve growth factor (NGF) exhibit significant protein synthesis.
• Actin dynamics are crucial for neuronal development and function, particularly neurite outgrowth.

Purpose of the Study:

• To investigate the changes in actin polymerization state during neuronal differentiation.
• To determine the rate of actin synthesis and its incorporation into cytoskeletal structures.

Main Methods:

• Culturing sympathetic neurons from chick embryos with NGF.
• Measuring total protein and actin content per cell.
• Assessing actin monomeric and filamentous states using DNase I inhibition assay.
• Utilizing radioactive leucine labeling and pulse-chase experiments to track actin synthesis and turnover.
• Employing DNase I-Sepharose affinity chromatography for actin isolation.

Main Results:

• Neuronal protein content increased 4-fold over 7 days in NGF-containing medium.
• The proportion of monomeric actin decreased significantly in mature, neurite-bearing neurons compared to rounded neurons.
• Actin in neurites was found to be almost entirely filamentous.
• Newly synthesized actin was rapidly incorporated into both sedimentable (filamentous) and non-sedimentable fractions.
• Actin exhibited similar specific activity in both fractions, suggesting rapid exchange between monomeric and filamentous pools in living cells.

Conclusions:

• Neuronal differentiation involves a significant shift towards filamentous actin.
• Newly synthesized actin is quickly incorporated into the actin cytoskeleton.
• A dynamic exchange mechanism exists for actin molecules between monomeric and filamentous pools within living sympathetic neurons.