Dynamic balance between activation and repression regulates pre-mRNA alternative splicing during heart development

Area of Science:

• Molecular Biology
• Developmental Biology
• Genetics

Background:

• Cardiac troponin T (cTNT) exon 5 splicing is developmentally regulated, present in embryonic but absent in adult hearts.
• Alternative splicing of cTNT is controlled by a balance of proteins promoting exon inclusion (CELF) and repressing it (PTB, MBNL).

Purpose of the Study:

• To investigate the changes in regulatory protein levels during heart development that cause the shift in cTNT alternative splicing.
• To determine the roles of CELF and PTB proteins in regulating cTNT splicing in cardiomyocytes.

Main Methods:

• Utilized dominant-negative proteins to assess the function of CELF and PTB in cardiomyocyte splicing.
• Examined the expression patterns of cTNT regulatory factors (CELF, PTB, MBNL1) during mouse and chicken heart development.

Main Results:

• Both CELF and PTB activities are essential for proper cTNT splicing in cardiomyocytes.
• Two CELF proteins, CUG-BP and ETR-3, decrease in adult hearts, correlating with the loss of exon inclusion.
• PTB and MBNL1 are expressed throughout heart development, while CELF proteins are down-regulated.

Conclusions:

• Developmental changes in cTNT splicing result from a balance between positive (CELF) and negative (PTB, MBNL) regulatory factors.
• Modulation of regulatory protein expression, particularly CELF proteins, drives developmental splicing changes.
• Down-regulation of CELF proteins during development suggests a broader role in tissue-specific splicing regulation.