Highlight on the dynamic organization of the nucleus

Abstract

The last decade has seen rapid advances in our understanding of the proteins of the nuclear envelope, which have multiple roles including positioning the nucleus, maintaining its structural organization, and in events ranging from mitosis and meiosis to chromatin positioning and gene expression. Diverse new and stimulating results relating to nuclear organization and genome function from across kingdoms were presented in a session stream entitled "Dynamic Organization of the Nucleus" at this year's Society of Experimental Biology (SEB) meeting in Brighton, UK (July 2016). This was the first session stream run by the Nuclear Dynamics Special Interest Group, which was organized by David Evans, Katja Graumann (both Oxford Brookes University, UK) and Iris Meier (Ohio State University, USA). The session featured presentations on areas relating to nuclear organization across kingdoms including the nuclear envelope, chromatin organization, and genome function.

Keywords: LINC complex; chromatin organization; gene expression; lamin; nuclear architecture; nuclear movement; nucleopore; nucleus.

Figure 1.

Highlight on functional components of the nuclear envelope across kingdoms. The fundamental units of the LINC complexes which mechanically couple the nucleoskeleton and cytoskeleton are KASH (Klarsicht, ANC-1 and SYNE homology) domain-containing nesprins and SUN (Sad-1 and UNC-84) domain-containing proteins. Although functionally conserved, most of those components identified in metazoans do not have sequence homologues across kingdoms. With the exception of SUN proteins (e.g., SUN1, SUN2 and SUN3), KASH proteins (e.g. WIP, WIT) present no homology with their animal functional equivalent (e.g., Nesprin, ANC-1, Klarsicht, UNC-83, KASH5 or MSP-300). Similarly, most of the inner nuclear envelope proteins gathered in the LEM2-emerin-MAN1 (LEM) domain protein family, do not yet have functional equivalent in plant. The LEM domain proteins share an ability to bind lamins and tether repressive chromatin at the nuclear periphery. These have homologues in Dictyostelium discoideum (Src1) and yeast (Heh1, Heh2 and Ima1) which in the absence of lamins, play a role in nuclear stiffening through chromatin tethering to the INM. The functional lamin-like proteins in plant are the nuclear matrix constituent proteins (NMCPs) also called crowded nuclei (CRWN) in Arabidopsis, while NE81 has been identified in protozoa. SUN1 and SUN2 bind CRWN1, whereas NMCP1 has several putative interactors including ARP7. In M. truncatula, the ion channel complex DMI1-CNGC15 which localize to both inner nuclear membrane (INM) and outer nuclear membrane (ONM), are required for symbiotic factor induced nuclear localized calcium release. At the nuclear pore complex (NPC), plant-specific FG-repeat nucleoporin, NUP136 and NUP82, have been identified. While the trypanosome NPC is predominantly symmetric, the yeast NPC is comparatively less so.