Abstract
Nuclear import is required for communication between the cytoplasm and the nucleus and to enact lasting changes in gene transcription following stimuli. Binding to an Importin-α molecule in the cytoplasm is often required to mediate nuclear entry of a signaling protein. As multiple isoforms of Importin-α exist, some may be responsible for the entry of distinct cargoes rather than general nuclear import. Indeed, in neuronal systems, Importin-α isoforms can mediate very specific processes such as axonal tiling and communication of an injury signal. To study nuclear import during development, we examined the expression and function of Importin-α2 in Drosophila melanogaster. We found that Importin-α2 was expressed in the nervous system where it was required for normal active zone density at the NMJ and axonal commissure formation in the central nervous system. Other aspects of synaptic morphology at the NMJ and the localization of other synaptic markers appeared normal in importin-α2 mutants. Importin-α2 also functioned in development of the body wall musculature. Mutants in importin-α2 exhibited errors in muscle patterning and organization that could be alleviated by restoring muscle expression of Importin-α2. Thus, Importin-α2 is needed for some processes in the development of both the nervous system and the larval musculature.
Highlights
To ensure a proper long-term response to stimuli, cells must have communication between the cytoplasm and the nucleus
The importin family comprises two major classes of protein: Importin-a and Importin-b [3]. These proteins form a ternary complex with a cargo molecule [4]: Importin-a mediates cargo binding through a nuclear localization signal (NLS) while Importin-b binds Importin-a and mediates translocation through the nuclear pore [5]
To examine the function and expression of Importin-a2 in Drosophila, we used the deletion imp-a2D14 [20], which removes the first half of the coding sequence (Figure 1A) and an antibody raised against the C-terminus of Importin-a2 [19]
Summary
To ensure a proper long-term response to stimuli, cells must have communication between the cytoplasm and the nucleus. The importin family comprises two major classes of protein: Importin-a and Importin-b [3] In many cases, these proteins form a ternary complex with a cargo molecule [4]: Importin-a mediates cargo binding through a nuclear localization signal (NLS) while Importin-b binds Importin-a and mediates translocation through the nuclear pore [5]. These proteins form a ternary complex with a cargo molecule [4]: Importin-a mediates cargo binding through a nuclear localization signal (NLS) while Importin-b binds Importin-a and mediates translocation through the nuclear pore [5] In this model, Importin-a confers cargo specificity to the import machinery [6] and is the necessary intermediary between the cargo and Importin-b. Elucidating the roles of different Importin-a homologues can illuminate both the general mechanisms of nuclear import and the specific contributions of individual importins to neuronal function
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