Two alternatively-spliced human nebulin isoforms with either exon 143 or exon 144 and their developmental regulation

Area of Science:

• Muscle biology
• Protein biochemistry
• Molecular genetics

Background:

• Nebulin is a large protein crucial for muscle contraction.
• Mutations in the NEB gene cause nemaline myopathy.
• Nebulin mRNA exhibits alternative splicing, including exon 143 or exon 144.

Purpose of the Study:

• To develop and utilize antibodies for analyzing nebulin isoforms at the protein level.
• To investigate the developmental expression patterns of nebulin isoforms containing exon 143 and exon 144.

Main Methods:

• Production of monoclonal antibodies specific to nebulin regions encoded by exon 143 and exon 144.
• Immunohistochemical staining of muscle sections and myotubes.
• Quantitative real-time PCR (qPCR) for mRNA analysis.

Main Results:

• Antibodies recognized nebulin proteins of expected size (600-900 kD) and stained sarcomeres.
• Newly-formed myotubes and early fetal muscle (12 weeks) predominantly expressed exon 144 nebulin.
• Exon 143 nebulin expression increased during fetal development (17 weeks) and showed variable, fiber-type-specific distribution in mature muscle.

Conclusions:

• Nebulin isoform with exon 144 serves as the default during early myogenesis.
• Regulated expression of nebulin containing exon 143 is a later developmental event.
• Differential expression of nebulin isoforms contributes to mature muscle heterogeneity.