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A unique subspecies of histone H4 mRNA from rat myoblasts contains poly(A)
Abstract:
Fractionation of rat L6 myoblast histone H4 mRNA into its three component subspecies revealed that one of the major subspecies (H4-1) contained poly(A). The unique poly(A)+ H4 mRNA makes up about 8% of the total polysomal H4 mRNA population detected. Unlike the poly(A)- histone mRNAs, whose levels are reduced by greater than 95% when myoblasts differentiate into myotubes, the poly(A)+ subspecies is reduced by only 70%. The poly(A)+ H4 mRNA from myotubes incubated with actinomycin D decays with a half-life of 37-42 min, which is similar to that obtained for the poly(A)- H4 mRNAs in myoblasts. Both the poly(A)+ and poly(A)- subspecies decay at an increased rate after inhibition of DNA synthesis. In myoblasts the poly(A)+ H4 mRNA exists almost exclusively in the polysomal compartment (greater than 95%) with little (less than 5%) in the free ribonucleoprotein (mRNA-protein or mRNP) complex compartment of the cell. Poly(A)- histone H4 mRNA subspecies, on the other hand, are distributed with approximately 80% in the polysomal compartment and 20% in the free mRNP complex compartment. The unique poly(A)+ H4 mRNA is unusual, not only in that it contains poly(A) but also in its behavior compared to poly(A)- H4 mRNAs during terminal differentiation.
Insights
A unique polyadenylated (poly(A)+) histone H4 messenger RNA (mRNA) was identified in rat L6 myoblasts. This poly(A)+ H4 mRNA behaves differently during cell differentiation compared to its non-polyadenylated counterparts.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Histone H4 mRNA exists in multiple subspecies.
- Polyadenylation of mRNA typically influences its stability and translation.
- Cell differentiation involves significant changes in gene expression.
Purpose of the Study:
- To characterize the unique poly(A)+ histone H4 mRNA subspecies.
- To investigate the role of polyadenylation in histone H4 mRNA regulation during myoblast differentiation.
Main Methods:
- Fractionation of rat L6 myoblast histone H4 mRNA.
- Detection and quantification of poly(A)+ and poly(A)- H4 mRNA subspecies.
- Analysis of mRNA decay rates using actinomycin D.
- Investigation of mRNA localization within cellular compartments (polysomal vs. free mRNP).
Main Results:
- A unique poly(A)+ H4 mRNA subspecies (H4-1) was identified, constituting approximately 8% of the total polysomal H4 mRNA.
- The poly(A)+ H4 mRNA showed reduced, but not abolished, decrease (70% reduction) during myoblast differentiation compared to poly(A)- H4 mRNAs (>95% reduction).
- Poly(A)+ H4 mRNA decay rates were similar to poly(A)- H4 mRNAs in myoblasts and increased upon DNA synthesis inhibition.
- Poly(A)+ H4 mRNA was predominantly found in polysomes (>95%), unlike poly(A)- H4 mRNAs which were distributed between polysomes (80%) and free mRNPs (20%).
Conclusions:
- The identified poly(A)+ H4 mRNA represents a distinct regulatory variant with unique properties.
- Polyadenylation appears to confer a degree of differentiation-resistant stability to H4 mRNA.
- The subcellular localization differs between poly(A)+ and poly(A)- H4 mRNA subspecies, suggesting distinct translational control mechanisms.