Regulation of transcript encoding the 43K subsynaptic protein during development and after denervation.

Area of Science:

• Neuroscience
• Molecular Biology
• Muscle Physiology

Background:

• Vertebrate neuromuscular synapses feature acetylcholine receptors (AChRs) and 43K subsynaptic protein at the postsynaptic membrane.
• While AChRs are typically localized to innervated adult muscle, they also appear in nonsynaptic regions of developing or denervated muscle.
• This nonsynaptic accumulation is linked to increased mRNA for AChR subunits, triggered by reduced muscle electrical activity.

Purpose of the Study:

• To investigate the expression patterns of the 43K subsynaptic protein mRNA during muscle development and after denervation.
• To compare the regulation of 43K protein mRNA levels with that of acetylcholine receptor (AChR) subunit mRNA.

Main Methods:

• Isolated cDNA encoding the 43K subsynaptic protein from Torpedo electric organ.
• Used this cDNA to isolate a homologous Xenopus laevis cDNA.
• Quantified 43K protein transcript levels in embryonic, innervated adult, and denervated adult muscle using RNase protection assays.

Main Results:

• Transcript levels for the 43K protein are low in innervated adult muscle.
• Denervation led to a 25- to 30-fold increase in 43K protein transcript levels.
• mRNA levels for the alpha subunit of AChR showed a similar increase upon denervation.
• Expression of transcripts for both 43K protein and AChR alpha subunit initiated coordinately during late gastrulation in embryonic muscle.

Conclusions:

• Transcripts for the 43K subsynaptic protein and AChR subunits are coordinately expressed during embryonic development.
• The expression of 43K protein mRNA is regulated by denervation, mirroring AChR subunit mRNA regulation.
• These findings highlight a coordinated molecular response in muscle development and in response to electrical activity loss.