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Abstract The orientation of the mitotic spindle at metaphase determines the placement of the daughter cells. Spindle orientation in animals typically relies on an evolutionarily conserved biological machine comprised of at least four proteins – called Pins, Gαi, Mud, and Dynein in flies – that exerts a pulling force on astral microtubules and reels the spindle into alignment. The canonical model for spindle orientation holds that the direction of pulling is determined by asymmetric placement of this machinery at the cell cortex. In most cell types, this placement is thought to be mediated by Pins, and a substantial body of literature is therefore devoted to identifying polarized cues that govern localized cortical enrichment of Pins. In this study we revisit the canonical model and find that it is incomplete. Spindle orientation in theDrosophilafollicular epithelium and embryonic ectoderm requires not only Pins localization but also direct interaction between Pins and the multifunctional protein Discs large. This requirement can be over‐ridden by interaction with another Pins interacting protein, Inscuteable.
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Interaction between Discs large and Pins/LGN/GPSM2: a comparison across species
ABSTRACT The orientation of the mitotic spindle determines the direction of cell division, and therefore contributes to tissue shape and cell fate. Interaction between the multifunctional scaffolding protein Discs large (Dlg) and the canonical spindle orienting factor GPSM2 (called Pins in Drosophila and LGN in vertebrates) has been established in bilaterian models, but its function remains unclear. We used a phylogenetic approach to test whether the interaction is obligate in animals, and in particular whether Pins/LGN/GPSM2 evolved in multicellular organisms as a Dlg-binding protein. We show that Dlg diverged in C. elegans and the syncytial sponge Opsacas minuta and propose that this divergence may correspond with differences in spindle orientation requirements between these organisms and the canonical pathways described in bilaterians. We also demonstrate that Pins/LGN/GPSM2 is present in basal animals, but the established Dlg-interaction site cannot be found in either Placozoa or Porifera. Our results suggest that the interaction between Pins/LGN/GPSM2 and Dlg appeared in Cnidaria, and we therefore speculate that it may have evolved to promote accurate division orientation in the nervous system. This work reveals the evolutionary history of the Pins/LGN/GPSM2-Dlg interaction and suggests new possibilities for its importance in spindle orientation during epithelial and neural tissue development.
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- Award ID(s):
- 2042280
- PAR ID:
- 10311379
- Date Published:
- Journal Name:
- Biology Open
- Volume:
- 10
- Issue:
- 11
- ISSN:
- 2046-6390
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Andrew, D (Ed.)Abstract Mud/NuMA/LIN-5 (in flies, vertebrates, and worms) is an evolutionarily conserved protein that regulates the shape and orientation of the mitotic spindle. In vertebrate cells, these functions depend on a C-terminal region called the NuMA-Tip, which (i) mediates interaction with the conserved partner protein LGN (called Pins in flies), (ii) contains a highly conserved subsequence called the NLM, and (ii) binds directly to microtubule ends. Although Mud plays a vital role in Drosophila mitosis, less is known about its structure, particularly at the C-terminus. Through sequence analysis and functional studies, we identify the Mud-Tip region and show that it is encoded by 3 consecutive exons. These exons are spliced out of several Mud isoforms, creating functionally distinct “Tipless” variants. We find that Tipless isoforms are specifically expressed in male and female gametes, where they localize to the nuclear envelope. Although Mud is known to be essential for female fertility, we demonstrate that this function does not require an intact Tip region. We also find that Mud antagonizes the localization of Lamin, a nucleoskeletal protein, in the testis, and uncover an unexpected role for Tipless Mud in promoting male fertility. Our work reveals that while the Mud-Tip is important for Mud function at mitosis, alternative splicing ensures this region is absent from Mud isoforms that perform a moonlighting role during meiosis.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1242/bio.058982
