ABSTRACT
Differential RNA metabolism regulates a wide array of developmental processes. Here, we describe a mechanism that controls the transition from premature Drosophila tendon precursors into mature muscle-bound tendon cells. This mechanism is based on the opposing activities of two isoforms of the RNA binding protein How. While the isoform How(L) is a negative regulator of Stripe, the key modulator of tendon cell differentiation, How(S) isoform elevates Stripe levels, thereby releasing the differentiation arrest induced by How(L). The opposing activities of the How isoforms are manifested by differential rates of mRNA degradation of the target stripe mRNA. This mechanism is conserved, as the mammalian RNA binding Quaking proteins may similarly affect the levels of Krox20, a regulator of Schwann cell maturation.
Subject(s)
Cell Differentiation , Drosophila/cytology , Drosophila/embryology , Nuclear Proteins , RNA-Binding Proteins/metabolism , Tendons/cytology , Tendons/embryology , 3' Untranslated Regions/genetics , 3' Untranslated Regions/metabolism , Alternative Splicing/genetics , Animals , Blotting, Western , Cell Line , DNA-Binding Proteins/biosynthesis , DNA-Binding Proteins/genetics , Drosophila/metabolism , Drosophila Proteins/chemistry , Drosophila Proteins/genetics , Drosophila Proteins/metabolism , Early Growth Response Protein 2 , Genes, Reporter/genetics , Nuclear Localization Signals , Protein Isoforms/chemistry , Protein Isoforms/genetics , Protein Isoforms/metabolism , RNA Stability , RNA-Binding Proteins/chemistry , RNA-Binding Proteins/genetics , Repressor Proteins/chemistry , Repressor Proteins/genetics , Repressor Proteins/metabolism , Tendons/metabolism , Transcription Factors/biosynthesis , Transcription Factors/geneticsABSTRACT
In Drosophila, a tendon cell is selected from a group of equipotent precursors following its interaction with a muscle cell. This interaction results in elevated levels of the transcription factor Stripe in the future tendon cells. Here we show that the balance between two distinct forms of the RNA-binding protein How maintains low levels of Stripe at the precursor stage and high levels in the mature tendon. The long, nuclear-specific protein How(L) downregulates Stripe protein levels at the precursor stage by binding stripe mRNA and inhibiting its nuclear export. This inhibition is likely to be counteracted by the short How(S) protein, present in both nucleus and cytoplasm, which is upregulated in the muscle-bound tendon cell following EGF receptor activation.
