Sun H et al. (2021) Nature "Temporal transitions in the post-mitotic nervous system of Caenorhabditis elegans."

Hobert O, Sun H

[Nature, 2021]

In most animals, the majority of the nervous system is generated and assembled into neuronal circuits during embryonic development¹. However, during juvenile stages, nervous systems still undergo extensive anatomical and functional changes to eventually form a fully mature nervous system by the adult stage^2,3. The molecular changes in post-mitotic neurons across post-embryonic development and the genetic programs that control these temporal transitions are not well understood^4,5. Here, using the model system Caenorhabditis elegans, we comprehensively characterized the distinct functional states (locomotor behaviour) and the corresponding distinct molecular states (transcriptome) of the post-mitotic nervous system across temporal transitions during post-embryonic development. We observed pervasive, neuron-type-specific changes in gene expression, many of which are controlled by the developmental upregulation of the conserved heterochronic microRNA LIN-4 and the subsequent promotion of a mature neuronal transcriptional program through the repression of its target, the transcription factor lin-14. The functional relevance of these molecular transitions are exemplified by a temporally regulated target gene of the LIN-14 transcription factor, nlp-45, a neuropeptide-encoding gene, which we find is required for several distinct temporal transitions in exploratory activity during post-embryonic development. Our study provides insights into regulatory strategies that control neuron-type-specific gene batteries to modulate distinct behavioural states across temporal, sexual and environmental dimensions of post-embryonic development.

Sun H et al. (2023) MicroPubl Biol "Comparing engineered nuclear-localized reporter cassettes."

Schafer W, Sun H, Beets I, Hobert O

[MicroPubl Biol, 2023]

Recent single-cell transcriptome analysis has revealed a tremendous breadth and specificity of neuropeptide-encoding gene expression in the nervous system of <i>C. elegans.</i> To analyze the dynamics of neuropeptide gene expression, as well as to dissect the regulatory mechanism by which their expression is controlled, reporter genes remain an important tool. Using CRISPR/Cas9 genome-engineering, we generate here reporter alleles for 6 different neuropeptide encoding genes (3 <i>flp</i> genes, 1 <i>nlp</i> and 2 insulin genes). We find that different reporter cassettes result in different levels of reporter expression and recommend usage of an SL2::GFP::H2B or GFP::H2B::SL2 cassette.

Sun H et al. (2007) Genetics "Modulation of Caenorhabditis elegans transcription factor activity by HIM-8 and the related Zinc-Finger ZIM proteins."

Nelms BL, Chamberlin HM, Sun H, Hanna-Rose W, Sleiman SF

[Genetics, 2007]

The previously reported negative regulatory activity of HIM-8 on the Sox protein EGL-13 is shared by the HIM-8-related ZIM proteins. Furthermore, mutation of HIM-8 can modulate the effects of substitution mutations in the DNA-binding domains of at least four other transcription factors, suggesting broad regulatory activity by HIM-8.

Sun H et al. (2002) Proc Natl Acad Sci U S A "The vitelliform macular dystrophy protein defines a new family of chloride channels."

Nathans J, Yau KW, Tsunenari T, Sun H

[Proc Natl Acad Sci U S A, 2002]

Vitelliform macular dystrophy (VMD/Best disease; MIM*153700) is an early-onset autosomal dominant disorder in which accumulation of lipofuscin-like material within and beneath the retinal pigment epithelium is associated with a progressive loss of central vision. Bestrophin, the protein product of the VMD gene, has four predicted transmembrane domains. There are multiple bestrophin homologues in the human, Drosophila, and Caenorhabditis elegans genomes, but no function has previously been ascribed to these proteins, and they show no detectable homology to other proteins of known function. Using heterologous expression, we show here that human, Drosophila, and C. elegans bestrophins form oligomeric chloride channels, and that human bestrophin is sensitive to intracellular calcium. Each of 15 missense mutations asscociated with VMD greatly reduces or abolishes the membrane current. Four of these mutant bestrophins were coexpressed with the wild type and each dominantly inhibited the wild-type membrane current, consistent with the dominant nature of the disease. These experiments establish the existence of a new chloride channel family and VMD as a channelopathy.

Baudrimont A et al. (2010) PLoS Genet "Leptotene/zygotene chromosome movement via the SUN/KASH protein bridge in Caenorhabditis elegans."

Pasierbek P, Machacek T, Penkner A, Klein F, Fridkin A, Woglar A, Baudrimont A, Jantsch V, Gruenbaum Y, Gloggnitzer J, Wegrostek C

[PLoS Genet, 2010]

The Caenorhabditis elegans inner nuclear envelope protein matefin/SUN-1 plays a conserved, pivotal role in the process of genome haploidization. CHK-2-dependent phosphorylation of SUN-1 regulates homologous chromosome pairing and interhomolog recombination in Caenorhabditis elegans. Using time-lapse microscopy, we characterized the movement of matefin/SUN-1::GFP aggregates (the equivalent of chromosomal attachment plaques) and showed that the dynamics of matefin/SUN-1 aggregates remained unchanged throughout leptonene/zygotene, despite the progression of pairing. Movement of SUN-1 aggregates correlated with chromatin polarization. We also analyzed the requirements for the formation of movement-competent matefin/SUN-1 aggregates in the context of chromosome structure and found that chromosome axes were required to produce wild-type numbers of attachment plaques. Abrogation of synapsis led to a deceleration of SUN-1 aggregate movement. Analysis of matefin/SUN-1 in a double-strand break deficient mutant revealed that repair intermediates influenced matefin/SUN-1 aggregate dynamics. Investigation of movement in meiotic regulator mutants substantiated that proper orchestration of the meiotic program and effective repair of DNA double-strand breaks were necessary for the wild-type behavior of matefin/SUN-1 aggregates.

Minn I et al. (2009) Mol Biol Cell "SUN-1 and ZYG-12, mediators of centrosome-nucleus attachment, are a functional SUN/KASH pair in Caenorhabditis elegans."

Minn I, Hanna-Rose W, Rolls MM, Malone CJ

[Mol Biol Cell, 2009]

Klarsicht/ANC-1/Syne/homology (KASH)/Sad-1/UNC-84 (SUN) protein pairs can act as connectors between cytoplasmic organelles and the nucleoskeleton. Caenorhabditis elegans ZYG-12 and SUN-1 are essential for centrosome-nucleus attachment. Although SUN-1 has a canonical SUN domain, ZYG-12 has a divergent KASH domain. Here, we establish that the ZYG-12 mini KASH domain is functional and, in combination with a portion of coiled-coil domain, is sufficient for nuclear envelope localization. ZYG-12 and SUN-1 are hypothesized to be outer and inner nuclear membrane proteins, respectively, and to interact, but neither their topologies nor their physical interaction has been directly investigated. We show that ZYG-12 is a type II outer nuclear membrane (ONM) protein and that SUN-1 is a type II inner nuclear membrane protein. The proteins interact in the luminal space of the nuclear envelope via the ZYG-12 mini KASH domain and a region of SUN-1 that does not include the SUN domain. SUN-1 is hypothesized to restrict ZYG-12 to the ONM, preventing diffusion through the endoplasmic reticulum. We establish that ZYG-12 is indeed immobile at the ONM by using fluorescence recovery after photobleaching and show that SUN-1 is sufficient to localize ZYG-12 in cells. This work supports current models of KASH/SUN pairs and highlights the diversity in sequence elements defining KASH domains.

Hao H et al. (2019) Nucleus "SUN/KASH interactions facilitate force transmission across the nuclear envelope."

Starr DA, Hao H

[Nucleus, 2019]

LINC complexes (Linker of Nucleoskeleton and Cytoskeleton), consisting of inner nuclear membrane SUN proteins and outer nuclear membrane KASH proteins, are essential for nuclear positioning, cell migration and chromosome dynamics. Crystal structures of the central SUN-KASH interaction domains revealed close interfaces predicted to mediate LINC complex formation and function. However, the in vivo significance of these conserved interactions were unclear. Cain et al (2018) used a combination of Caenorhabditis elegans genetics, imaging in cultured NIH 3T3 fibroblasts, and Molecular Dynamic simulations, to study SUN-KASH interactions in cells. The study found that a conserved aromatic residue at the -7 position of the C-terminal KASH domain and conserved cysteines in both the KASH and SUN domains play important roles in force transmission across the nuclear envelope. Other properties of LINC complexes may also play significant roles in transmitting mechanical forces generated by the cytoskeleton across the nuclear envelope. For example, the helicies preceding the SUN domain activate SUN proteins and may be important for activating KASH-SUN interactions or for association of SUN and/or KASH proteins with the membrane. The longer coiled-coils spanning the perinuclear space may also play a role in mediating force transmission. Finally, LINC complexes may be arranged in higher-order structures to facilitate high force-bearing processes.

Cain NE et al. (2014) J Cell Biol "The SUN protein UNC-84 is required only in force-bearing cells to maintain nuclear envelope architecture."

McDonald KL, Cain NE, Tapley EC, Starr DA, Cain BM

[J Cell Biol, 2014]

The nuclear envelope (NE) consists of two evenly spaced bilayers, the inner and outer nuclear membranes. The Sad1p and UNC-84 (SUN) proteins and Klarsicht, ANC-1, and Syne homology (KASH) proteins that interact to form LINC (linker of nucleoskeleton and cytoskeleton) complexes connecting the nucleoskeleton to the cytoskeleton have been implicated in maintaining NE spacing. Surprisingly, the NE morphology of most Caenorhabditis elegans nuclei was normal in the absence of functional SUN proteins. Distortions of the perinuclear space observed in unc-84 mutant muscle nuclei resembled those previously observed in HeLa cells, suggesting that SUN proteins are required to maintain NE architecture in cells under high mechanical strain. The UNC-84 protein with large deletions in its luminal domain was able to form functional NE bridges but had no observable effect on NE architecture. Therefore, SUN-KASH bridges are only required to maintain NE spacing in cells subjected to increased mechanical forces. Furthermore, SUN proteins do not dictate the width of the NE.

Penkner A et al. (2007) Dev Cell "The nuclear envelope protein Matefin/SUN-1 is required for homologous pairing in C. elegans meiosis."

Penkner A, Gruenbaum Y, Loidl J, Jantsch V, Tang L, Schweizer D, Novatchkova M, Fridkin A, Ladurner M

[Dev Cell, 2007]

We identify a highly specific mutation (jf18) in the Caenorhabditis elegans nuclear envelope protein matefin MTF-1/SUN-1 that provides direct evidence for active involvement of the nuclear envelope in homologous chromosome pairing in C. elegans meiosis. The reorganization of chromatin in early meiosis is disrupted in mtf-1/sun-1(jf18) gonads, concomitant with the absence of presynaptic homolog alignment. Synapsis is established precociously and nonhomologously. Wild-type leptotene/zygotene nuclei show patch-like aggregations of the ZYG-12 protein, which fail to develop in mtf-1/sun-1(jf18) mutants. These patches remarkably colocalize with a component of the cis-acting chromosomal pairing center (HIM-8) rather than the centrosome. Our data on this mtf-1/sun-1 allele challenge the previously postulated role of the centrosome/spindle organizing center in chromosome pairing, and clearly support a role for MTF-1/SUN-1 in meiotic chromosome reorganization and in homolog recognition, possibly by mediating local aggregation of the ZYG-12 protein in meiotic nuclei.

Penkner AM et al. (2009) Cell "Meiotic chromosome homology search involves modifications of the nuclear envelope protein Matefin/SUN-1."

Jantsch V, Ammerer G, Woglar A, Machacek T, Fridkin A, Pasierbek P, Gruenbaum Y, Penkner AM, Gloggnitzer J, Baudrimont A, Csaszar E

[Cell, 2009]

Genome haploidization during meiosis depends on recognition and association of parental homologous chromosomes. The C. elegans SUN/KASH domain proteins Matefin/SUN-1 and ZYG-12 have a conserved role in this process. They bridge the nuclear envelope, connecting the cytoplasm and the nucleoplasm to transmit forces that allow chromosome movement and homolog pairing and prevent nonhomologous synapsis. Here, we show that Matefin/SUN-1 forms rapidly moving aggregates at putative chromosomal attachment sites in the meiotic transition zone (TZ). We analyzed requirements for aggregate formation and identified multiple phosphotarget residues in the nucleoplasmic domain of Matefin/SUN-1. These CHK-2 dependent phosphorylations occur in leptotene/zygotene, diminish during pachytene and are involved in pairing. Mimicking phosphorylation causes an extended TZ and univalents at diakinesis. Our data suggest that the properties of the nuclear envelope are altered during the time window when homologs are sorted and Matefin/SUN-1 aggregates form, thereby controling the movement, homologous pairing and interhomolog recombination of chromosomes.