Makorin RING zinc-finger protein 1-dependent translational control of dendritic mRNAs in mammalian neurons

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In nerve cells, distinct forms of learning and memory require new protein synthesis, which can occur locally at synapses by translation of select mRNA species residing in dendrites. These new proteins permit synapse-specific remodelling in response to synaptic activation. However, to date the molecular mechanisms controlling dendritic translation are only sparsely understood. In mammalian brain neurons, makorin RING zinc-finger protein 1 (MKRN1), an interaction partner of poly(A)-binding protein, associates with several dendritically localized transcripts. In vivo in the rat brain, it specifically accumulates at activated synapses. Moreover, functional assays show that MKRN1 stimulates translation initiation of reporter mRNAs in neurons. This and additional evidence indicate that MKRN1 regulates activity-dependent translation of dendritic mRNAs at synapses. Our goal is to characterize the MKRN1-mediated translational control mechanisms in neurons. In particular, we will address the following issues: i. We will determine whether distinct synaptic signaling cascades modulate the activity of MKRN1. Specifically, we want to analyze how the selective stimulation or inhibition of individual signaling components in neurons influences MKRN1-mediated translational control of reporter mRNAs. ii. Translation is a highly complex process with numerous factors involved. We intend to characterize molecules that structurally and functionally link MKRN1 to the translation machinery. Cellular complexes harbouring MKRN1 will be biochemically purified and individual components will be identified by mass spectrometry. Subsequently, the physiological significance of individual proteins will be assessed using small interfering (si)RNA technology. iii. MKRN1 is a bona fide RNA-binding protein. By performing immunoprecipitations after in vivo UV-crosslinking of protein/RNA complexes we want to identify MKRN1 mRNA targets in rodent brain. Afterwards we will investigate if MKRN1 regulates translation of these mRNAs. We expect our results to be relevant for a better understanding of activity-dependent translational control mechanisms operating on dendritic mRNAs. This will provide new insights into the molecular processes underlying learning and memory as well as cognitive deficits in mammals.