POLR1A, encoding the largest subunit of RNA Polymerase I, is crucial for ribosomal RNA (rRNA) transcription, a rate-limiting step in ribosome biogenesis essential for cell survival and protein translation [2,3,4]. Ribosome biogenesis is a global process, and disruptions in this pathway can lead to tissue-specific disorders known as ribosomopathies [3]. Genetic models, such as KO/CKO mouse models, are valuable for studying POLR1A's functions.

In mouse models, conditional mutagenesis of Polr1a in neural crest cells (involved in face and heart development), the second heart field (related to cardiac outflow tract and right ventricle), and forebrain precursors showed that loss of Polr1a causes cell-autonomous apoptosis, resulting in embryonic malformations. This reveals its importance in these developmental lineages [1]. NCC-specific deletion of Polr1a in mice diminishes rRNA synthesis, leading to p53 protein accumulation, NCC apoptosis, and craniofacial anomalies, highlighting its role in craniofacial development [2]. In a zebrafish model of Acrofacial Dysostosis-Cincinnati type, polr1a loss-of-function led to perturbed ribosome biogenesis, p53-dependent cell death, and craniofacial anomalies due to a deficiency of neural-crest-derived skeletal precursor cells [4]. Also, inhibiting tp53 in polr1a-/-mutant zebrafish embryos suppressed neuroepithelial apoptosis but could not fully rescue cartilage development, indicating both Tp53-dependent and independent signaling downstream of polr1a in ribosome biogenesis during neural crest cell and craniofacial development [3].

In conclusion, POLR1A is essential for rRNA transcription and ribosome biogenesis, which are crucial for cell survival and proliferation. Studies using KO/CKO mouse and zebrafish models have revealed its significant role in craniofacial, neural, and cardiac development, and in the pathogenesis of ribosomopathies such as Acrofacial Dysostosis-Cincinnati type [1,2,3,4].