Nuclear phosphatidylinositol 4,5-bisphosphate islets contribute to efficient RNA polymerase II-dependent transcription

Abstract

This paper describes a novel type of nuclear structure - nuclear lipid islets (NLIs). They are of 40-100 nm with a lipidic interior, and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P] molecules comprise a significant part of their surface. Most of NLIs have RNA at the periphery. Consistent with that, RNA is required for their integrity. The NLI periphery is associated with Pol II transcription machinery, including the largest Pol II subunit, transcription factors and NM1 (also known as NMI). The PtdIns(4,5)P-NM1 interaction is important for Pol II transcription, since NM1 knockdown reduces the Pol II transcription level, and the overexpression of wild-type NM1 [but not NM1 mutated in the PtdIns(4,5)P-binding site] rescues the transcription. Importantly, Pol II transcription is dependent on NLI integrity, because an enzymatic reduction of the PtdIns(4,5)P level results in a decrease of the Pol II transcription level. Furthermore, about half of nascent transcripts localise to NLIs, and transcriptionally active transgene loci preferentially colocalise with NLIs. We hypothesize that NLIs serve as a structural platform that facilitates the formation of Pol II transcription factories, thus participating in the formation of nuclear architecture competent for transcription.

Multiple Aspects of PIP2 Involvement in C. elegans Gametogenesis

“…Based on our data we concluded that the observed C. elegans phenotypes might be caused by (i) the altered chromosome structure; (ii) impaired ubiquitin-proteasome pathway; or (iii) disrupted binding of PIP2 to some essential proteins. Based on our data presented here and already published data in mammalian cell lines [ 16 , 17 , 18 ], we propose that PIP2 is involved in the regulation of the molecular processes at multiple levels, and may be a part of many protein complexes in the C. elegans germ cells nuclei.…”

“…However, we did not observe any obvious asymmetrical localization of PIP2 in the embryos, and thus provide more support for another proposal, that PPK-1 might influence the spindle positioning independently of its function as a PIP2 producer. Suggestions about the independent role of PI5PK and PIP2 were previously published by us [ 18 ] and Chakrabarti et al for the regulation of the RNA polymerase I transcription in mammalian cells [ 46 ].…”

“…On the other hand, PPK-1 per se may contribute to the regulation of these processes independently of its function as a PIP2 producer, and possibly by the interaction with different protein binding partners, too. Previously, a distinct role of PIP2 and its kinase has been described, based on the binding partners for mammalian cell lines [ 18 , 46 ]. Partially, some of the observed phenotypes might be indirect, caused by the decrease of the second messengers produced by the PIP2 cleavage.…”

“…PIP2 localization to plasma membrane, nuclear speckles, small foci in the nucleoplasm, and to the nucleolus were described in mammalian cells [ 13 , 14 , 15 , 16 , 17 ]. It is known that nuclear PIP2 acts as a transcription activator or repressor interacting with various protein complexes of RNA polymerases I and II, or with the histone demethylase [ 15 , 16 , 17 , 18 ]. PIP2 regulates the RNA polymerase II transcription apparently by the direct interaction with histone H1 and H3, shielding the positive charges of the histones and thus competing with their ability to bind DNA [ 19 ].…”

Yeast Sphingolipid Phospholipase Gene ISC1 Regulates the Spindle Checkpoint by a CDC55-Dependent Mechanism

“…These findings raise a number of intriguing questions on the localization and physical organization of lipids in the nucleus; however, an increasing on June 18, 2020 at SYDDANSK UNIVERSITETSBIBLIOTEK http://mcb.asm.org/ Downloaded from body of literature points to the presence of specific bioactive lipids in the nucleus [46][47][48][49]. Moreover, studies in mammals have also detected neutral sphingomyelinase (the mammalian counterpart of ISC1) [50][51][52][53][54] and sphingomyelin in the nucleus [55].…”