Actα, Actβ, and Actγ transcripts are found in motoneurons in vivo and in vitro. (A) Cresyl violet staining of spinal cord sections. Somata of motoneurons (MNs; white circles) were cut from ventral horn of E18 embryos and adult mice using laser capture microdissection. Bars, 200 µm. RNA was extracted and analyzed by quantitative RT-PCR. (B and C) Absolute copy numbers of mRNAs of actin isoforms were normalized to absolute copies of Gapdh. Actα, Actβ, and Actγ mRNAs are detected in E18 stage (n = 3) and adult (n = 4) motoneurons (*, P < 0.05; **, P < 0.0016; ***, P < 0.0005). (D) ChAT transcripts were detected in RNA samples of E18 and adult microdissected motoneurons but were undetectable in cultured cerebellar neurons and heart tissues. (E) Motoneuron cultures in microfluidic chambers. Axonal growth toward the axonal compartment was supported by a BDNF gradient. RNA was separately extracted from somatodendritic and axonal compartments and used for quantitative RT-PCR analysis. (F) Quantitative RT-PCR amplification curves for Actα, Actβ, Actγ, Gapdh mRNAs, and 18sRNA obtained from somatodendritic and axonal compartments. Histone H10 mRNAs were detected only in somatodendritic compartments. (G and H) Absolute quantification of quantitative RT-PCR data shows that the mRNA levels of Actβ are higher than mRNA levels of Actα and Actγ in both somatodendritic (***, P < 0.0004) and axonal compartments (*, P < 0.018 for n = 6). (I) Ratio of mRNA levels of actin isoforms in somatodendritic versus axonal compartment revealed a relatively high enrichment of Actα transcripts in the axonal compartment (***, P < 0.0003). Shown are mean ± SEM. One-way ANOVA with Bonferroni post hoc test was used for statistical analysis.