Date Published: November 30, 2009
Publisher: Public Library of Science
Author(s): Andrew K. Shepherd, Ravinder Singh, Cedric S. Wesley, Juan Valcarcel. http://doi.org/10.1371/journal.pone.0008063
Abstract: Notch receptor regulates differentiation of almost all tissues and organs during animal development. Many mechanisms function at the protein level to finely regulate Notch activity. Here we provide evidence for Notch regulation at an earlier step – mRNA 3′ processing. Processing at the Notch consensus polyadenylation site appears by default to be suppressed in Drosophila embryos. Interference with this suppression, by a mutation, results in increased levels of polyadenylated Notch mRNA, excess Notch signaling, and severe developmental defects. We propose that Notch mRNA 3′ processing is negatively regulated to limit the production of Notch protein and render it a controlling factor in the generation of Notch signaling.
Partial Text: Notch (N) signaling specifies binary cell fates and refines morphological patterns during differentiation of almost all tissues or organs in animals. N, a cell surface receptor, and Delta, a cell surface anchored ligand, mediate N signaling. N and Delta binding results in the release of the N intracellular domain (Nintra) from the cell surface. Nintra translocates to the nucleus and activates transcription of target genes. Cells that suppress N signaling commit to one developmental fate whereas cells that activate N signaling commit to the alternative developmental fate –. N signaling is very finely and tightly regulated. A mere 1.5–2X difference in gene dosage, or very low levels of constitutive activation, results in mutant phenotypes –. A number of mechanisms function at the level of N protein modification, trafficking, recycling, and degradation to regulate N activity –, –. Whether N activity is regulated at the level of mRNA as well is uncertain.
Our data show that the original Nnd1 allele, which is designated Nnd1-dse, is mutated in the DSE of the consensus poly(A) site of the N gene. DSE is well known to be required for mRNA 3′ processing and polyadenylation. Thus, a mutation in the N DSE was expected to reduce N mRNA 3′ processing and polyadenylation. We find the contrary result: N mRNA 3′ processing and polyadenylation is increased in Nnd1-dse embryos. Accordingly, N signaling is excessive in these embryos and embryogenesis is severely disrupted.