Yun Kee

The Mammalian Brain rsec6/8 Complex

rsec6 and rsec8 are two components of a 17S complex in mammalian brain that is homologous to the yeast 834 kDa Sec6/8/15 complex which is essential for exocytosis. Purification and partial amino acid sequencing of the mammalian rsec6/8 complex reveals that it is composed of eight novel proteins with a combined molecular weight of 743 kDa. The complex is broadly expressed in brain and displays a plasma membrane localization in nerve terminals. Membrane associated rsec6/8 complex coimmunoprecipitates with syntaxin, a plasma membrane protein critical for neurotransmission. These data suggest a role for the mammalian rsec6/8 complex in neurotransmitter release via interactions with the core vesicle docking and fusion apparatus.

Distinct domains of syntaxin are required for synaptic vesicle fusion complex formation and dissociation.

Membrane fusion resulting in neurotransmitter secretion forms the basis of neural communication. Three multimeric complexes of the protein syntaxin are important in this process: syntaxin and n-sec1; syntaxin, VAMP, and SNAP-25; and syntaxin, VAMP, SNAP-25, alpha SNAP, and NSF (20S complex). In this report, we demonstrate that unique, yet overlapping, domains of syntaxin are required to form these complexes. The formation of higher order heteromultimers has a set of structural requirements distinct from those required for dimeric interactions. Dissociation of the 20S complex by NSF following ATP hydrolysis requires amino-terminal regions of syntaxin that are outside of the binding domains for the 20S constituent proteins. These data are consistent with the hypothesis that conformational changes in syntaxin, resulting from protein-protein interactions and ATP hydrolysis by NSF, mediate neurotransmitter release.

Genomic mismatch scanning: a new approach to genetic linkage mapping

Genomic mismatch scanning (GMS) is a new method of genetic linkage analysis that does not require conventional polymorphic markers or gel electrophoresis. GMS is ideally suited to affected–relative–pair mapping. DNA fragments from all regions of identity–by–descent between two relatives are isolated based on their ability to form extensive mismatch–free hybrid molecules. The genomic origin of this selected pool of DNA fragments is then mapped in a single hybridization step. Here we demonstrate the practicality of GMS in a model organism, Saccharomyces cerevisiae. GMS is likely to be applicable to other organisms, including humans, and may be of particular value in mapping complex genetic traits.

Id4 expression and its relationship to other Id genes during avian embryonic development

We present the sequence and expression pattern of chick Id4 and compare its distribution to that of other vertebrate Id genes. At early stages, Id4 expression is discrete, with transcript transiently expressed in subsets of migrating neural crest cells, the dorsal myocardium, the segmental plate mesoderm, and the tail bud. Later, expression is also observed in the telencephalic vesicles and corneal epithelium. Of all the Id genes, Id4 exhibits the most restricted pattern in the developing nervous system, with little expression in the presumptive neural crest or placodes. Id4 appears in the neural tube much later than other Id genes. However, all four Id genes display overlapping patterns in the branchial arches and tail bud.

Temporally and spatially restricted expression of the helix–loop–helix transcriptional regulator Id1 during avian embryogenesis

We isolated the chick orthologue of the Id1 helix-loop-helix gene and analyzed its expression pattern during early chick embryo development by whole-mount in situ hybridization. The Id1 expression pattern is dynamic and confined to discrete locations including the neural plate border, prospective olfactory placode, hindbrain, mesenchyme of distal branchial arches and adjacent to placodes, and the distal mesoderm of the limb buds.

The transcriptional regulator Id3 is expressed in cranial sensory placodes during early avian embryonic development.

The chick homologue of the helix-loop-helix gene Id3 was isolated, and its expression pattern was analyzed during early stages of chick development. Chick Id3 is dynamically expressed in the olfactory, lens, and otic placodes. It is also observed in the epiphysis, nephric primordium, stomodeum, dermomyotome, distal branchial arches, dorsolateral hindbrain, foregut endoderm, dorsal spinal cord, and somites.

Nanobody-targeted E3-ubiquitin ligase complex degrades nuclear proteins

Targeted protein degradation is a powerful tool in determining the function of specific proteins or protein complexes. We fused nanobodies to SPOP, an adaptor protein of the Cullin-RING E3 ubiquitin ligase complex, resulting in rapid ubiquitination and subsequent proteasome-dependent degradation of specific nuclear proteins in mammalian cells and zebrafish embryos. This approach is easily modifiable, as substrate specificity is conferred by an antibody domain that can be adapted to target virtually any protein.

Live image profiling of neural crest lineages in zebrafish transgenic lines

Zebrafish transgenic lines are important experimental tools for lineage tracing and imaging studies. It is crucial to precisely characterize the cell lineages labeled in transgenic lines to understand their limitations and thus properly interpret the data obtained from their use; only then can we confidently select a line appropriate for our particular research objectives. Here we profiled the cell lineages labeled in the closely related neural crest transgenic lines Tg(foxd3:GFP), Tg(sox10:eGFP) and Tg(sox10:mRFP). These fish were crossed to generate embryos, in which foxd3 and sox10 transgenic neural crest labeling could be directly compared at the cellular level using live confocal imaging. We have identified key differences in the cell lineages labeled in each line during early neural crest development and demonstrated that the most anterior cranial neural crest cells initially migrating out of neural tube at the level of forebrain and anterior midbrain express sox10:eGFP and sox10:mRFP, but not foxd3:GFP. This differential profile was robustly maintained in the different-tiating progeny of the neural crest lineages until 3.5dpf. Our data will enable researchers to make an informed choice in selecting transgenic lines for future neural crest research.

Benzyl Isothiocyanate Suppresses High-Fat Diet- Stimulated Mammary Tumor Progression via the Alteration of Tumor Microenvironments in Obesity-Resistant BALB/c Mice

We previously reported that a high‐fat diet (HFD) and M2‐macrophages induce changes in tumor microenvironments and stimulate tumor growth and metastasis of 4T1 mammary cancer cells in BALB/c mice. In this study, we attempted to determine whether benzyl isothiocyanate (BITC) inhibits HFD‐induced changes in tumor progression and in tumor microenvironments. Four groups of female BALB/c mice (4‐week‐old) were fed on a control diet (CD, 10 kcal% fat) and HFD (60 kcal% fat) containing BITC (0, 25, or 100 mg/kg diet) for 20 weeks. Following 16 weeks of feeding, 4T1 cells (5 × 104 cells) were injected into the mammary fat pads, and animals were killed 30 d after the injection. HFD feeding increased solid tumor growth and the number of tumor nodules in the lung and liver, as compared to the CD group, and these increases were inhibited by BITC supplementation. The number of lipid vacuoles, CD45+ leukocytes and CD206+ M2‐macrophages, expression of Ki67, levels of cytokines/chemokines, including macrophage‐colony stimulating factor (M‐CSF) and monocyte chemoattractant protein‐1, and mRNA levels of F4/80, CD86, Ym1, CD163, CCR2, and M‐CSF receptor were increased in the tumor tissues of HFD‐fed mice, and these increases were inhibited by BITC supplementation. In vitro culture results demonstrated that BITC inhibited macrophage migration as well as lipid droplet accumulation in 3T3‐L1 cells. These results suggest that suppression of lipid accumulation and macrophage infiltration in tumor tissues may be one of the mechanisms by which BITC suppresses tumor progression in HFD‐fed mice.

3D Light-Sheet Fluorescence Microscopy of Cranial Neurons and Vasculature during Zebrafish Embryogenesis.

Precise 3D spatial mapping of cells and their connections within living tissues is required to fully understand developmental processes and neural activities. Zebrafish embryos are relatively small and optically transparent, making them the vertebrate model of choice for live in vivo imaging. However, embryonic brains cannot be imaged in their entirety by confocal or two-photon microscopy due to limitations in optical range and scanning speed. Here, we use light-sheet fluorescence microscopy to overcome these limitations and image the entire head of live transgenic zebrafish embryos. We simultaneously imaged cranial neurons and blood vessels during embryogenesis, generating comprehensive 3D maps that provide insight into the coordinated morphogenesis of the nervous system and vasculature during early development. In addition, blood cells circulating through the entire head, vagal and cardiac vasculature were also visualized at high resolution in a 3D movie. These data provide the foundation for the construction of a complete 4D atlas of zebrafish embryogenesis and neural activity.