Multiple roles of the furrow deepening Ca2+ transient during cytokinesis in zebrafish embryos

Lipid Polarization during Cytokinesis

The plasma membrane of eukaryotic cells is composed of a large number of lipid species that are laterally segregated into functional domains as well as asymmetrically distributed between the outer and inner leaflets. Additionally, the spatial distribution and organization of these lipids dramatically change in response to various cellular states, such as cell division, differentiation, and apoptosis. Division of one cell into two daughter cells is one of the most fundamental requirements for the sustenance of growth in all living organisms. The successful completion of cytokinesis, the final stage of cell division, is critically dependent on the spatial distribution and organization of specific lipids. In this review, we discuss the properties of various lipid species associated with cytokinesis and the mechanisms involved in their polarization, including forward trafficking, endocytic recycling, local synthesis, and cortical flow models. The differences in lipid species requirements and distribution in mitotic vs. male meiotic cells will be discussed. We will concentrate on sphingolipids and phosphatidylinositols because their transbilayer organization and movement may be linked via the cytoskeleton and thus critically regulate various steps of cytokinesis.

Functional roles of the SHCBP1 and KIF23 interaction in modulating the cell-cycle and cisplatin resistance of head and neck squamous cell carcinoma

BACKGROUND

This study aimed to explore the functional roles of Shc SH2-domain-binding protein 1 (SHCBP1) and Kinesin Family Member 23 (KIF23) in HPV-negative head and neck squamous cell carcinoma (HNSCC).

METHODS

Bioinformatic analysis was conducted using data from The Cancer Genome Atlas (TCGA) and GSE103322. HNSCC cell lines were used for in vitro and in vivo analysis.

RESULTS

SHCBP1 upregulation was associated with unfavorable survival. SHCBP1 knockdown reduced cell proliferation and increased the cisplatin sensitivity of SCC9/SCC25 cells. SHCBP1 interacted with KIF23 via its Nesd homology domain (NHD) domain, which was important for its nucleus localization. SHCBP1 positively modulated KIF23 expression and activated phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt), extracellular signal regulated kinase (ERK)1/2, nuclear factor kappa B (NF/κB)-p65, and Wnt/β-catenin signaling. KIF23 knockdown abrogated cisplatin resistance induced by SHCBP1 overexpression.

CONCLUSION

SHCBP1 interacts with KIF23 and cooperatively regulates cell-cycle progression and cisplatin resistance of HNSCC tumor cells.

In vivo Functional Genomics for Undiagnosed Patients: The Impact of Small GTPases Signaling Dysregulation at Pan-Embryo Developmental Scale

While individually rare, disorders affecting development collectively represent a substantial clinical, psychological, and socioeconomic burden to patients, families, and society. Insights into the molecular mechanisms underlying these disorders are required to speed up diagnosis, improve counseling, and optimize management toward targeted therapies. Genome sequencing is now unveiling previously unexplored genetic variations in undiagnosed patients, which require functional validation and mechanistic understanding, particularly when dealing with novel nosologic entities. Functional perturbations of key regulators acting on signals' intersections of evolutionarily conserved pathways in these pathological conditions hinder the fine balance between various developmental inputs governing morphogenesis and homeostasis. However, the distinct mechanisms by which these hubs orchestrate pathways to ensure the developmental coordinates are poorly understood. Integrative functional genomics implementing quantitative in vivo models of embryogenesis with subcellular precision in whole organisms contribute to answering these questions. Here, we review the current knowledge on genes and mechanisms critically involved in developmental syndromes and pediatric cancers, revealed by genomic sequencing and in vivo models such as insects, worms and fish. We focus on the monomeric GTPases of the RAS superfamily and their influence on crucial developmental signals and processes. We next discuss the effectiveness of exponentially growing functional assays employing tractable models to identify regulatory crossroads. Unprecedented sophistications are now possible in zebrafish, i.e., genome editing with single-nucleotide precision, nanoimaging, highly resolved recording of multiple small molecules activity, and simultaneous monitoring of brain circuits and complex behavioral response. These assets permit accurate real-time reporting of dynamic small GTPases-controlled processes in entire organisms, owning the potential to tackle rare disease mechanisms.

Sensory Neuroblast Quiescence Depends on Vascular Cytoneme Contacts and Sensory Neuronal Differentiation Requires Initiation of Blood Flow

In many organs, stem cell function depends on communication with their niche partners. Cranial sensory neurons develop in close proximity to blood vessels; however, whether vasculature is an integral component of their niches is yet unknown. Here, two separate roles for vasculature in cranial sensory neurogenesis in zebrafish are uncovered. The first involves precise spatiotemporal endothelial-neuroblast cytoneme contacts and Dll4-Notch signaling to restrain neuroblast proliferation. The second, instead, requires blood flow to trigger a transcriptional response that modifies neuroblast metabolic status and induces sensory neuron differentiation. In contrast, no role of sensory neurogenesis in vascular development is found, suggesting unidirectional signaling from vasculature to sensory neuroblasts. Altogether, we demonstrate that the cranial vasculature constitutes a niche component of the sensory ganglia that regulates the pace of their growth and differentiation dynamics.

KIF23 enhances cell proliferation in pancreatic ductal adenocarcinoma and is a potent therapeutic target

Background

In recent research, high expression of kinesin family member 23 (KIF23), one of the kinesin motor proteins involved in the regulation of cytokinesis, has been shown to be related to poor prognosis in glioma and paclitaxel-resistant gastric cancer, as a results of the enhancement of proliferation, migration, and invasion. In this study, we analyzed the role of KIF23 in the progression of pancreatic ductal adenocarcinoma.

Methods

A bioinformatic method was used to analyze the KIF23 mRNA level in pancreatic tumor tissues compared with normal pancreatic tissues and to analyze the connection between high KIF23 expression and prognosis. We examined the expression of KIF23 using immunohistochemistry and analyzed the connection between the expression of KIF23 and clinicopathological features in pancreatic ductal adenocarcinoma patients. In addition, a colony formation assay, MTT assay, and western blot assay were performed in vitro, along with a mouse xenograft model in vivo, to analyze the effect of KIF23 on proliferation. Further, the correlation between KIF23 and CDCA8 was analyzed by TCGA and immunohistochemical data.

Results

Bioinformatic results showed that KIF23 mRNA expression was higher in pancreatic tumor tissues than in normal pancreatic tissues and a poor prognosis has been linked to the high expression of KIF23. Immunohistochemistry revealed that KIF23 was highly expressed at the protein level and high expression of KIF23 correlated with adverse clinicopathological features. Our experimental results demonstrated that knockdown of KIF23 could inhibit the proliferation of pancreatic cells. Further, a positive correlation between KIF23 and CDCA8 expression existed, and KIF23 might promote pancreatic cancer proliferation by affecting CDCA8 expression.

Conclusions

Our data showed that high expression of KIF23 is associated with a poor prognosis, and KIF23 might be a potential therapeutic target for pancreatic ductal adenocarcinoma.

The role of the cytoskeleton in germ plasm aggregation and compaction in the zebrafish embryo

The transmission of genetic information from one generation to another is crucial for survival of animal species. This is accomplished by the induction of primordial germ cells (PGCs) that will eventually establish the germline. In some animals the germline is induced by signals in gastrula, whereas in others it is specified by inheritance of maternal determinants, known as germ plasm. In zebrafish, aggregation and compaction of maternally derived germ plasm during the first several embryonic cell cycles is essential for generation of PGCs. These processes are controlled by cellular functions associated with the cellular division apparatus. Ribonucleoparticles containing germ plasm components are bound to both the ends of astral microtubules and a dynamic F-actin network through a mechanism integrated with that which drives the cell division program. In this chapter we discuss the role that modifications of the cell division apparatus, including the cytoskeleton and cytoskeleton-associated proteins, play in the regulation of zebrafish germ plasm assembly.

Regulation and Assembly of Actomyosin Contractile Rings in Cytokinesis and Cell Repair

Cytokinesis and single-cell wound repair both involve contractile assemblies of filamentous actin (F-actin) and myosin II organized into characteristic ring-like arrays. The assembly of these actomyosin contractile rings (CRs) is specified spatially and temporally by small Rho GTPases, which trigger local actin polymerization and myosin II contractility via a variety of downstream effectors. We now have a much clearer view of the Rho GTPase signaling cascade that leads to the formation of CRs, but some factors involved in CR positioning, assembly, and function remain poorly understood. Recent studies show that this regulation is multifactorial and goes beyond the long-established Ca²⁺ -dependent processes. There is substantial evidence that the Ca²⁺ -independent changes in cell shape, tension, and plasma membrane composition that characterize cytokinesis and single-cell wound repair also regulate CR formation. Elucidating the regulation and mechanistic properties of CRs is important to our understanding of basic cell biology and holds potential for therapeutic applications in human disease. In this review, we present a primer on the factors influencing and regulating CR positioning, assembly, and contraction as they occur in a variety of cytokinetic and single-cell wound repair models. Anat Rec, 301:2051-2066, 2018. © 2018 Wiley Periodicals, Inc.

Slow calcium waves mediate furrow microtubule reorganization and germ plasm compaction in the early zebrafish embryo

Zebrafish germ plasm ribonucleoparticles (RNPs) become recruited to furrows of early zebrafish embryos through their association with astral microtubules ends. During the initiation of cytokinesis, microtubules are remodeled into a furrow microtubule array (FMA), which is thought to be analogous to the mammalian midbody involved in membrane abscission. During furrow maturation, RNPs and FMA tubules transition from their original distribution along the furrow to enrichments at the furrow distal ends, which facilitates germ plasm mass compaction. We show that nebel mutants exhibit reduced furrow-associated slow calcium waves (SCWs), caused at least in part by defective enrichment of calcium stores. RNP and FMA distal enrichment mirrors the medial-to-distal polarity of SCWs, and inhibition of calcium release or downstream mediators such as Calmodulin affects RNP and FMA distal enrichment. Blastomeres with reduced or lacking SCWs, such as early blastomeres in nebel mutants and wild-type blastomeres at later stages, exhibit medially bundling microtubules similar to midbodies in other cell types. Our data indicate that SCWs provide medial-to-distal directionality along the furrow to facilitate germ plasm RNP enrichment at the furrow ends.

Myosin-1 inhibition by PClP affects membrane shape, cortical actin distribution and lipid droplet dynamics in early Zebrafish embryos

Myosin-1 (Myo1) represents a mechanical link between the membrane and actin-cytoskeleton in animal cells. We have studied the effect of Myo1 inhibitor PClP in 1-8 cell Zebrafish embryos. Our results indicate a unique involvement of Myo1 in early development of Zebrafish embryos. Inhibition of Myo1 (by PClP) and Myo2 (by Blebbistatin) lead to arrest in cell division. While Myo1 isoforms appears to be important for both the formation and the maintenance of cleavage furrows, Myo2 is required only for the formation of furrows. We found that the blastodisc of the embryo, which contains a thick actin cortex (~13 μm), is loaded with cortical Myo1. Myo1 appears to be crucial for maintaining the blastodisc morphology and the actin cortex thickness. In addition to cell division and furrow formation, inhibition of Myo1 has a drastic effect on the dynamics and distribution of lipid droplets (LDs) in the blastodisc near the cleavage furrow. All these results above are effects of Myo1 inhibition exclusively; Myo2 inhibition by blebbistatin does not show such phenotypes. Therefore, our results demonstrate a potential role for Myo1 in the maintenance and formation of furrow, blastodisc morphology, cell-division and LD organization within the blastodisc during early embryogenesis.

Ca2+ Signalling and Membrane Dynamics During Cytokinesis in Animal Cells

Interest in the role of Ca²⁺ signalling as a possible regulator of the combinatorial processes that result in the separation of the daughter cells during cytokinesis, extend back almost a 100 years. One of the key processes required for the successful completion of cytokinesis in animal cells (especially in the large holoblastically and meroblastically dividing embryonic cells of a number of amphibian and fish species), is the dynamic remodelling of the plasma membrane. Ca²⁺ signalling was subsequently demonstrated to regulate various different aspects of cytokinesis in animal cells, and so here we focus specifically on the role of Ca²⁺ signalling in the remodelling of the plasma membrane. We begin by providing a brief history of the animal models used and the research accomplished by the early twentieth century investigators, with regards to this aspect of animal cell cytokinesis. We then review the most recent progress made (i.e., in the last 10 years), which has significantly advanced our current understanding on the role of cytokinetic Ca²⁺ signalling in membrane remodelling. To this end, we initially summarize what is currently known about the Ca²⁺ transients generated during animal cell cytokinesis, and then we describe the latest findings regarding the source of Ca²⁺ generating these transients. Finally, we review the current evidence about the possible targets of the different cytokinetic Ca²⁺ transients with a particular emphasis on those that either directly or indirectly affect plasma membrane dynamics. With regards to the latter, we discuss the possible role of the early Ca²⁺ signalling events in the deformation of the plasma membrane at the start of cytokinesis (i.e., during furrow positioning), as well as the role of the subsequent Ca²⁺ signals in the trafficking and fusion of vesicles, which help to remodel the plasma membrane during the final stages of cell division. As it is becoming clear that each of the cytokinetic Ca²⁺ transients might have multiple, integrated targets, deciphering the precise role of each transient represents a significant (and ongoing) challenge.

SOCE proteins, STIM1 and Orai1, are localized to the cleavage furrow during cytokinesis of the first and second cell division cycles in zebrafish embryos

In zebrafish embryos, distinct Ca2+ transients are localized to the early cleavage furrows during the first few cell division cycles. These transients are generated mainly by release via IP3Rs in the endoplasmic reticulum, and they are necessary for furrow positioning, propagation, deepening and apposition. We previously showed, via the use of inhibitors, that store-operated Ca2+ entry (SOCE) also appears to be essential for maintaining the IP3R-mediated elevated levels of [Ca2+]i for the extended periods required for the completion of successful furrow deepening and daughter cell apposition in these large embryonic cells. Here, newly fertilized, dechorionated embryos were fixed at various times during the first and second cell division cycles and immunolabelled with antibodies to STIM1 and/or Orai1 (key components of SOCE). We show that both of these proteins have a dynamic pattern of localization during cytokinesis of the first two cell division cycles. These new data help to support our previous inhibitor results, and provide additional evidence that SOCE contributes to the maintenance of the sustained elevated Ca2+ that is required for the successful completion of cytokinesis in the large cells of embryonic zebrafish.

aura (mid1ip1l) regulates the cytoskeleton at the zebrafish egg-to-embryo transition

Embryos from females homozygous for a recessive maternal-effect mutation in the gene aura exhibit defects including reduced cortical integrity, defective cortical granule (CG) release upon egg activation, failure to complete cytokinesis, and abnormal cell wound healing. We show that the cytokinesis defects are associated with aberrant cytoskeletal reorganization during furrow maturation, including abnormal F-actin enrichment and microtubule reorganization. Cortical F-actin prior to furrow formation fails to exhibit a normal transition into F-actin-rich arcs, and drug inhibition is consistent with aura function promoting F-actin polymerization and/or stabilization. In mutants, components of exocytic and endocytic vesicles, such as Vamp2, Clathrin and Dynamin, are sequestered in unreleased CGs, indicating a need for CG recycling in the normal redistribution of these factors. However, the exocytic targeting factor Rab11 is recruited to the furrow plane normally at the tip of bundling microtubules, suggesting an alternative anchoring mechanism independent of membrane recycling. A positional cloning approach indicates that the mutation in aura is associated with a truncation of Mid1 interacting protein 1 like (Mid1ip1l), previously identified as an interactor of the X-linked Opitz G/BBB syndrome gene product Mid1. A Cas9/CRISPR-induced mutant allele in mid1ip1l fails to complement the originally isolated aura maternal-effect mutation, confirming gene assignment. Mid1ip1l protein localizes to cortical F-actin aggregates, consistent with a direct role in cytoskeletal regulation. Our studies indicate that maternally provided aura (mid1ip1l) acts during the reorganization of the cytoskeleton at the egg-to-embryo transition and highlight the importance of cytoskeletal dynamics and membrane recycling during this developmental period.

Vascular Mural Cells Promote Noradrenergic Differentiation of Embryonic Sympathetic Neurons

The sympathetic nervous system controls smooth muscle tone and heart rate in the cardiovascular system. Postganglionic sympathetic neurons (SNs) develop in close proximity to the dorsal aorta (DA) and innervate visceral smooth muscle targets. Here, we use the zebrafish embryo to ask whether the DA is required for SN development. We show that noradrenergic (NA) differentiation of SN precursors temporally coincides with vascular mural cell (VMC) recruitment to the DA and vascular maturation. Blocking vascular maturation inhibits VMC recruitment and blocks NA differentiation of SN precursors. Inhibition of platelet-derived growth factor receptor (PDGFR) signaling prevents VMC differentiation and also blocks NA differentiation of SN precursors. NA differentiation is normal in cloche mutants that are devoid of endothelial cells but have VMCs. Thus, PDGFR-mediated mural cell recruitment mediates neurovascular interactions between the aorta and sympathetic precursors and promotes their noradrenergic differentiation.

Characterization of tweety gene (ttyh1-3) expression in Xenopus laevis during embryonic development

The tweety family of genes encodes large-conductance chloride channels and has been implicated in a wide array of cellular processes including cell division, cell adhesion, regulation of calcium activity, and tumorigenesis, particularly in neuronal cells. However, their expression patterns during early development remain largely unknown. Here, we describe the spatial and temporal patterning of ttyh1, ttyh2, and ttyh3 in Xenopus laevis during early embryonic development. Ttyh1 and ttyh3 are initially expressed at the late neurula stage are and primarily localized to the developing nervous system; however ttyh1 and ttyh3 both show transient expression in the somites. By swimming tadpole stages, all three genes are expressed in the brain, spinal cord, eye, and cranial ganglia. While ttyh1 is restricted to proliferative, ventricular zones, ttyh3 is primarily localized to postmitotic regions of the developing nervous system. Ttyh2, however, is strongly expressed in cranial ganglia V, VII, IX and X. The differing temporal and spatial expression patterns of ttyh1, ttyh2, and ttyh3 suggest that they may play distinct roles throughout embryonic development.

Calcium signaling in extraembryonic domains during early teleost development

It is becoming recognized that the extraembryonic domains of developing vertebrates, that is, those that make no cellular contribution to the embryo proper, act as important signaling centers that induce and pattern the germ layers and help establish the key embryonic axes. In the embryos of teleost fish, in particular, significant progress has been made in understanding how signaling activity in extraembryonic domains, such as the enveloping layer, the yolk syncytial layer, and the yolk cell, might help regulate development via a combination of inductive interactions, cellular dynamics, and localized gene expression. Ca(2+) signaling in a variety of forms that include propagating waves and standing gradients is a feature found in all three teleostean extraembryonic domains. This leads us to propose that in addition to their other well-characterized signaling activities, extraembryonic domains are well suited (due to their relative stability and continuity) to act as Ca(2+) signaling centers and conduits.

Biphasic assembly of the contractile apparatus during the first two cell division cycles in zebrafish embryos

The large and optically clear embryos of the zebrafish provide an excellent model system in which to study the dynamic assembly of the essential contractile band components, actin and myosin, via double fluorescent labelling in combination with confocal microscopy. We report the rapid appearance (i.e. within <2 min) of a restricted arc of F-actin patches along the prospective furrow plane in a central, apical region of the blastodisc cortex. These patches then fused with each other end-to-end forming multiple actin cables, which were subsequently bundled together forming an F-actin band. During this initial assembly phase, the F-actin-based structure did not elongate laterally, but was still restricted to an arc extending ~15° either side of the blastodisc apex. This initial assembly phase was then followed by an extension phase, where additional F-actin patches were added to each end of the original arc, thus extending it out to the edges of the blastodisc. The dynamics of phosphorylated myosin light chain 2 (MLC2) recruitment to this F-actin scaffold also reflect the two-phase nature of the contractile apparatus assembly. MLC2 was not associated with the initial F-actin arc, but MLC2 clusters were recruited and assembled into the extending ends of the band. We propose that the MLC2-free central region of the contractile apparatus acts to position and then extend the cleavage furrow in the correct plane, while the actomyosin ends alone generate the force required for furrow ingression. This biphasic assembly strategy may be required to successfully divide the early cells of large embryos.

Membrane dynamics during cytokinesis

Endocytic membrane transport has recently emerged as a key process required for the successful completion of cytokinesis. Specific endocytic membranes act in concert with the cytoskeleton and ESCRT proteins to regulate the various stages of cytokinesis. In this review, we focus on the different endocytic Arf and Rab GTPases and their interaction proteins that regulate organelle transport to the intracellular bridge during cytokinesis. The identity and function of these endocytic organelles during the late stages of cell division will also be discussed.

HIV Assembly and Budding: Ca(2+) Signaling and Non-ESCRT Proteins Set the Stage

More than a decade has elapsed since the link between the endosomal sorting complex required for transport (ESCRT) machinery and HIV-1 protein trafficking and budding was first identified. L domains in HIV-1 Gag mediate recruitment of ESCRT which function in bud abscission releasing the viral particle from the host cell. Beyond virus budding, the ESCRT machinery is also involved in the endocytic pathway, cytokinesis, and autophagy. In the past few years, the number of non-ESCRT host proteins shown to be required in the assembly process has also grown. In this paper, we highlight the role of recently identified cellular factors that link ESCRT machinery to calcium signaling machinery and we suggest that this liaison contributes to setting the stage for productive ESCRT recruitment and mediation of abscission. Parallel paradigms for non-ESCRT roles in virus budding and cytokinesis will be discussed.

ESCRT machinery potentiates HIV-1 utilization of the PI(4,5)P(2)-PLC-IP3R-Ca(2+) signaling cascade

Human immunodeficiency virus type 1 (HIV-1) release efficiency is directed by late (L) domain motifs in the viral structural precursor polyprotein Gag, which serve as links to the ESCRT (endosomal sorting complex required for transport) machinery. Linkage is normally through binding of Tsg101, an ESCRT-1 component, to the P(7)TAP motif in the p6 region of Gag. In its absence, budding is directed by binding of Alix, an ESCRT adaptor protein, to the LY(36)PX(n)L motif in Gag. We recently showed that budding requires activation of the inositol 1,4,5-triphosphate receptor (IP3R), a protein that "gates" Ca(2+) release from intracellular stores, triggers Ca(2+) cell influx and thereby functions as a major regulator of Ca(2+) signaling. In the present study, we determined whether the L domain links Gag to Ca(2+) signaling machinery. Depletion of IP3R and inactivation of phospholipase C (PLC) inhibited budding whether or not Tsg101 was bound to Gag. PLC hydrolysis of phosphatidylinositol-(4,5)-bisphosphate generates inositol (1,4,5)-triphosphate, the ligand that activates IP3R. However, with Tsg101 bound, Gag release was independent of Gq-mediated activation of PLC, and budding was readily enhanced by pharmacological stimulation of PLC. Moreover, IP3R was redistributed to the cell periphery and cytosolic Ca(2+) was elevated, events indicative of induction of Ca(2+) signaling. The results suggest that L domain function, ESCRT machinery and Ca(2+) signaling are linked events in Gag release.

Downregulation of KIF23 suppresses glioma proliferation

To identify therapeutic molecular targets for glioma, we performed modified serological identification of antigens by recombinant complementary DNA (cDNA) expression cloning using sera from a mouse glioma model. Two clones, kinesin family member 23 (Kif23) and structural maintenance of chromosomes 4 (Smc4), were identified as antigens through immunological reaction with sera from mice harboring synergic GL261 mouse glioma and intratumoral inoculation with a mutant herpes simplex virus. The human Kif23 homolog KIF23 is a nuclear protein that localizes to the interzone of mitotic spindles, acting as a plus-end-directed motor enzyme that moves antiparallel microtubules in vitro. Expression analysis revealed a higher level of KIF23 expression in glioma tissues than in normal brain tissue. The introduction of small interfering RNA (siRNA) targeting KIF23 into two different glioma cell lines, U87MG and SF126, downregulated KIF23 expression, which significantly suppressed glioma cell proliferation in vitro. KIF23 siRNA-treated glioma cells exhibited larger cell bodies with two or more nuclei compared with control cells. In vivo analysis using mouse xenograft showed that KIF23 siRNA/DNA chimera-treated tumors were significantly smaller than tumors treated with control siRNA/DNA chimera. Taken together, our results indicate that downregulation of KIF23 decreases proliferation of glioma cells and that KIF23 may be a novel therapeutic target in malignant glioma.

Live imaging of the cytoskeleton in early cleavage-stage zebrafish embryos

The large and transparent cells of cleavage-stage zebrafish embryos provide unique opportunities to study cell division and cytoskeletal dynamics in very large animal cells. Here, we summarize recent progress, from our laboratories and others, on live imaging of the microtubule and actin cytoskeletons during zebrafish embryonic cleavage. First, we present simple protocols for extending the breeding competence of zebrafish mating ensembles throughout the day, which ensures a steady supply of embryos in early cleavage, and for mounting these embryos for imaging. Second, we describe a transgenic zebrafish line [Tg(bactin2:HsENSCONSIN17-282-3xEGFP)hm1] that expresses the green fluorescent protein (GFP)-labeled microtubule-binding part of ensconsin (EMTB-3GFP). We demonstrate that the microtubule-based structures of the early cell cycles can be imaged live, with single microtubule resolution and with high contrast, in this line. Microtubules are much more easily visualized using this tagged binding protein rather than directly labeled tubulin (injected Alexa-647-labeled tubulin), presumably due to lower background from probe molecules not attached to microtubules. Third, we illustrate live imaging of the actin cytoskeleton by injection of the actin-binding fragment of utrophin fused to GFP. Fourth, we compare epifluorescence-, spinning-disc-, laser-scanning-, and two-photon-microscopic modalities for live imaging of the microtubule cytoskeleton in early embryos of our EMTB-3GFP-expressing transgenic line. Finally, we discuss future applications and extensions of our methods.

A role for tumor protein TPD52 phosphorylation in endo-membrane trafficking during cytokinesis

Tumor protein D52 is expressed at high levels in exocrine cells containing large secretory granules where it regulates Ca(2+)-dependent protein secretion; however, D52 expression is also highly induced in multiple cancers. The present study investigated a role for the Ca(2+)-dependent phosphorylation of D52 at the single major phospho-acceptor site serine 136 on cell division. Ectopic expression of wild type D52 (D52wt) and the phosphomutants serine 136/alanine (S136A) or serine 136/glutamate (S136/E) resulted in significant multinucleation of cells. D52wt and S136/E each resulted in a greater than 2-fold increase in multinucleated cells compared to plasmid-transfected controls whereas the S136/A phospho-null mutant caused a 9-fold increase in multinucleation at 48h post-transfection. Electron microscopy revealed D52 expression induced a marked accumulation of vesicles along the mid-line between nuclei where the final stages of cell abscission normally occurs. Supporting this, D52wt strongly colocalized on vesicular structures containing the endosomal regulatory protein vesicle associated membrane protein 8 (VAMP 8) and this colocalization significantly increased with elevations in cellular Ca(2+). As VAMP 8 is known to be necessary for the endo-membrane fusion reactions that mediate the final stages of cytokinesis, these data indicate that D52 expression and phosphorylation at serine 136 play an important role in supporting the Ca(2+)-dependent membrane trafficking events necessary for cytokinesis in rapidly proliferating cancer cells.

Vertebrate maternal-effect genes: Insights into fertilization, early cleavage divisions, and germ cell determinant localization from studies in the zebrafish

In the earliest stages of animal development prior to the commencement of zygotic transcription, all critical cellular processes are carried out by maternally-provided molecular products accumulated in the egg during oogenesis. Disruption of these maternal products can lead to defective embryogenesis. In this review, we focus on maternal genes with roles in the fundamental processes of fertilization, cell division, centrosome regulation, and germ cell development with emphasis on findings from the zebrafish, as this is a unique and valuable model system for vertebrate reproduction.

Cloning and characterization of voltage-gated calcium channel alpha1 subunits in Xenopus laevis during development

Voltage-gated calcium channels play a critical role in regulating the Ca2+ activity that mediates many aspects of neural development, including neural induction, neurotransmitter phenotype specification, and neurite outgrowth. Using Xenopus laevis embryos, we describe the spatial and temporal expression patterns during development of the 10 pore-forming alpha1 subunits that define the channels' kinetic properties. In situ hybridization indicates that CaV1.2, CaV2.1, CaV2.2, and CaV3.2 are expressed during neurula stages throughout the neural tube. These, along with CaV1.3 and CaV2.3, beginning at early tail bud stages, and CaV3.1 at late tail bud stages, are detected in complex patterns within the brain and spinal cord through swimming tadpole stages. Additional expression of various alpha1 subunits was observed in the cranial ganglia, retina, olfactory epithelium, pineal gland, and heart. The unique expression patterns for the different alpha1 subunits suggests they are under precise spatial and temporal regulation and are serving specific functions during embryonic development.

Making the cut: the chemical biology of cytokinesis

Cytokinesis is the last step in the cell cycle, where daughter cells finally separate. It is precisely regulated in both time and space to ensure that each daughter cell receives an equal share of DNA and other cellular materials. Chemical biology approaches have been used very successfully to study the mechanism of cytokinesis. In this review, we discuss the use of small molecule probes to perturb cytokinesis, as well as the role naturally occurring small molecule metabolites such as lipids play during cytokinesis.