RNA Biol. 2025 Mar 24. doi: 10.1080/15476286.2025.2483118. Online ahead of print.
ABSTRACT
Cellular differentiation requires highly coordinated action of all three transcriptional systems to produce rRNAs, mRNAs, and various ‘short’ and ‘long’ non-coding RNAs by RNA Polymerase I, II, and III systems, respectively. The RNA Polymerase I catalyzes transcription of about 400 copies of mammalian rDNA genes, generating 18S, 5.8S, and 28S rRNA molecules. Lens fibre cell differentiation is a unique process to study transcriptional mechanisms of individual crystallin genes as their very high transcriptional outputs are directly comparable only to globin genes in erythrocytes. Importantly, both terminally differentiated lens fibre cells and mammalian erythrocytes degrade their nuclei though by different mechanisms. In lens, the generation of the organelle-free zone (OFZ) includes the degradation of mitochondria, endoplasmic reticulum, Golgi apparatus, and nuclei. Here, using RNA fluorescence in situ hybridization (FISH) we evaluated nascent rRNA transcription, located in the nucleoli, during the process of mouse lens fibre cell differentiation. Lens fibre cell nuclei undergo morphological changes including chromatin condensation prior to their denucleation. Remarkably, nascent rRNA transcription persists in all nuclei that are in direct proximity of the OFZ. Additionally, changes in both nuclei and nucleoli shape were evaluated via immunofluorescence detection of fibrillarin, nucleolin, UBF, and other proteins. These studies demonstrate for the first time that highly condensed lens fibre cell nuclei have the capacity to support nascent rRNA transcription. Thus, we propose that ‘late’ production of rRNA molecules and consequently of ribosomes increases crystallin protein synthesis machinery within the mature lens fibres.
PMID:40126102 | DOI:10.1080/15476286.2025.2483118