RESUMO
Ribosome biogenesis is a global process required for growth and proliferation of all cells, yet perturbation of ribosome biogenesis during human development often leads to tissue-specific defects termed ribosomopathies. Transcription of the ribosomal RNAs (rRNAs) by RNA polymerases (Pol) I and III, is considered a rate limiting step of ribosome biogenesis and mutations in the genes coding for RNA Pol I and III subunits, POLR1C and POLR1D cause Treacher Collins syndrome, a rare congenital craniofacial disorder. Our understanding of the functions of individual RNA polymerase subunits, however, remains poor. We discovered that polr1c and polr1d are dynamically expressed during zebrafish embryonic development, particularly in craniofacial tissues. Consistent with this pattern of activity, polr1c and polr1d homozygous mutant zebrafish exhibit cartilage hypoplasia and cranioskeletal anomalies characteristic of humans with Treacher Collins syndrome. Mechanistically, we discovered that polr1c and polr1d loss-of-function results in deficient ribosome biogenesis, Tp53-dependent neuroepithelial cell death and a deficiency of migrating neural crest cells, which are the primary progenitors of the craniofacial skeleton. More importantly, we show that genetic inhibition of tp53 can suppress neuroepithelial cell death and ameliorate the skeletal anomalies in polr1c and polr1d mutants, providing a potential avenue to prevent the pathogenesis of Treacher Collins syndrome. Our work therefore has uncovered tissue-specific roles for polr1c and polr1d in rRNA transcription, ribosome biogenesis, and neural crest and craniofacial development during embryogenesis. Furthermore, we have established polr1c and polr1d mutant zebrafish as models of Treacher Collins syndrome together with a unifying mechanism underlying its pathogenesis and possible prevention.
Assuntos
Anormalidades Craniofaciais/genética , RNA Polimerases Dirigidas por DNA/genética , Disostose Mandibulofacial/genética , Crista Neural/crescimento & desenvolvimento , Animais , Diferenciação Celular/genética , Anormalidades Craniofaciais/fisiopatologia , RNA Polimerases Dirigidas por DNA/biossíntese , Deficiências do Desenvolvimento/genética , Deficiências do Desenvolvimento/fisiopatologia , Modelos Animais de Doenças , Desenvolvimento Embrionário/genética , Humanos , Disostose Mandibulofacial/fisiopatologia , Mutação , Proteína Supressora de Tumor p53/genética , Peixe-Zebra/genética , Peixe-Zebra/crescimento & desenvolvimentoRESUMO
BACKGROUND: The single spanning transmembrane amyloid precursor protein (APP) and its proteolytic product, amyloid-beta (Ab) peptide, have been intensely studied due to their role in the pathogenesis of Alzheimer's disease. However, the biological role of the secreted ectodomain of APP, which is also generated by proteolytic cleavage, is less well understood. Here, we report Tol2 red fluorescent protein (RFP) transposon gene trap integrations in the zebrafish amyloid precursor protein a (appa) and amyloid precursor-like protein 2 (aplp2) genes. The transposon integrations are predicted to disrupt the appa and aplp2 genes to primarily produce secreted ectodomains of the corresponding proteins that are fused to RFP. RESULTS: Our results indicate the Appa-RFP and Aplp2 fusion proteins are likely secreted from the central nervous system and accumulate in the embryonic veins independent of blood flow. CONCLUSIONS: The zebrafish appa and aplp2 transposon insertion alleles will be useful for investigating the biological role of the secreted form of APP.
