Practice question

Nuclear interior contains skeletal framework operationally defined as material insoluble after detergent extraction, DNase digestion and high-salt removal of chromatin. This nuclear matrix comprises lamins A and B at periphery plus internal matrin family proteins Matrin-3, Matrin F, hnRNPs, SAF-A and actin-related proteins that form ten nanometer filaments and fibrogranular networks visible by resinless embedding EM. Matrin-3 is RNA- and DNA-binding protein with zinc-finger domains retaining hyperedited RNAs and anchoring matrix attachment regions to organize loops, mutated in familial amyotrophic lateral sclerosis. Lamin B remains associated throughout extraction, lamin A/C contributes to internal foci. Kinesin and dynein are microtubule motors functioning in cytoplasm, actin and myosin generate contractile forces in cytoplasm not nucleus except for nuclear myosin one, SNARE and COPI mediate vesicle fusion and coating in secretory pathway not nucleus. Matrix organizes replication factories, transcription hubs and splicing speckles, providing structural context for genome function. Integration with cell cycle kinases, calcium signaling and mechanical cues ensures coordinated remodeling during growth, migration and differentiation.