Knowledge Mapping of Opuntia Milpa Alta Since 1998: A Scientometric Analysis

Opuntia Milpa Alta is a cactus cultivated, domesticated, hybridized and selected from the plant Opuntia ficus-indica by Mexican agricultural experts, which can be used as fruit and vegetable. Opuntia Milpa Alta leaves and fruit are superior to wild varieties and suitable for storage and transportation. In 1998, Opuntia Milpa Alta was introduced to China from Mexico by the Quality Product Development Center of the Ministry of Agriculture of China. Up to now, the Opuntia Milpa Alta has been cultivated on a certain scale in China. This study aims to identify the research progress and development trends of Opuntia Milpa Alta in China. Papers published between 1998 to 2019 from two major Chinese academic databases (CNKI and Wangfang) with a topic search related to Opuntia Milpa Alta were collected. The research progress and development trends were analyzed based on CiteSpace software of text mining and visualization. The analysis found that Opuntia Milpa Alta has gone through three obvious research phases after being introduced to China. In the first phase, the researchers paid attention to its cultivation method. Subsequently, researchers began to use extraction methods to extract some of its components, such as polysaccharides and flavonoids. Finally, these extracted ingredients began to be used in some biomedical research.     

Expression of neurexin and neuroligin in the enteric nervous system and their down-regulated expression levels in Hirschsprung disease

To investigate the expression levels of neurexins and neuroligins in the enteric nervous system (ENS) in Hirschsprung Disease (HSCR). Longitudinal muscles with adherent mesenteric plexus were obtained by dissection of the fresh gut wall of mice, guinea pigs, and humans. Double labeling of neurexin I and Hu (a neuron marker), neuroligin 1 and Hu, neurexin I and synaptophysin (a presynaptic marker), and neuroligin 1 and PSD95 (a postsynaptic marker) was performed by immunofluorescence staining. Images were merged to determine the relative localizations of the proteins. Expression levels of neurexin and neuroligin in different segments of the ENS in HSCR were investigated by immunohistochemistry. Neurexin and neuroligin were detected in the mesenteric plexus of mice, guinea pigs, and humans with HSCR. Neurexin was located in the presynapse, whereas neuroligin was located in the postsynapse. Expression levels of neurexin and neuroligin were significant in the ganglionic colonic segment of HSCR, moderate in the transitional segment, and negative in the aganglionic colonic segment. The expressions of neurexin and neuroligin in the transitional segments were significantly down-regulated compared with the levels in the normal segments (P < 0.05). Expression levels of neurexin and neuroligin in ENS are significantly down-regulated in HSCR, which may be involved in the pathogenesis of HSCR.     

Molecular characterization of the tobacco SET domain protein NtSET1 unravels its role in histone methylation, chromatin binding, and segregation

Plants contain a great number of genes encoding a distinctive class of SET domain proteins which harbor a plant-specific N-terminal part together with a C-terminal part showing highest sequence similarity to the catalytic domain of the yeast CLR4, the human SUV39H1 and G9a histone-methyltransferases (HMTases). Here we show that NtSET1, a representative member of this class from tobacco, methylated both K9 and K27 of histone H3 in vitro. Ectopic expression of NtSET1, by an inducible promoter, increased the amount of dimethylated H3K9 and induced chromosome-segregation defects in tobacco BY2 cells. Deletion analyses show that the HMTase activity, the association with specific chromatin regions and with condensed chromosomes, and the cellular effects largely depended on the C-terminal region including the SET domain of the protein. Nevertheless, the N-terminal part of NtSET1 was capable of targeting the green fluorescent protein to interphase chromatin. Finally, we show that NtSET1 bound LHP1, the Arabidopsis homolog of animal heterochromatin protein 1 (HP1), and that LHP1 co-localized with heterochromatin containing high amounts of dimethylated H3K9, suggesting a role for NtSET1 in heterochromatic function. Taken together, our results provide new insights into the molecular and global chromatin-binding activities of this particular class member of plant SET domain proteins.     

Serpin polymerization is prevented by a hydrogen bond network that is centered on his-334 and stabilized by glycerol

Polymerization of serpins commonly results from mutations in the shutter region underlying the bifurcation of strands 3 and 5 of the A-sheet, with entry beyond this point being barred by a H-bond network centered on His-334. Exposure of this histidine in antithrombin, which has a partially opened sheet, allows polymerization and peptide insertion to occur at pH 6 or less when His-334 will be predictably protonated with disruption of the H-bond network. Similarly, thermal stability of antithrombin is pH-dependent with a single unfolding transition at pH 6, but there is no such transition when His-334 is buried by a fully closed A-sheet in heparin-complexed antithrombin or in alpha(1)-antitrypsin. Replacement of His-334 in alpha(1)-antitrypsin by a serine or alanine at pH 7.4 results in the same polymerization and loop-peptide acceptance observed with antithrombin at low pH. The critical role of His-334 and the re-formation of its H-bond network by the conserved P8 threonine, on the full insertion of strand 4, are relevant for the design of therapeutic blocking agents. This is highlighted here by the crystallographic demonstration that glycerol, which at high concentrations blocks polymerization, can replace the P8 threonine and re-form the disrupted H-bond network with His-334.     

The N-terminal 24 amino acids of the p55 gamma regulatory subunit of phosphoinositide 3-kinase binds Rb and induces cell cycle arrest

Although phosphoinositide 3-kinase (PI 3-kinase) is essential for cell cycle progression, the molecular mechanisms that regulate its diverse biological effects are poorly understood. We demonstrate here that Rb, a key regulator of cell cycle progression, associates with p55 kDa (p55alpha and p55gamma) regulatory subunits of PI 3-kinase in vivo and in vitro. Both confocal microscopy and biochemical analysis demonstrated the presence of p55gamma in the nucleus. The 24-amino-acid N-terminal end of p55gamma, which is unique among PI 3-kinase regulatory subunits, was sufficient to bind Rb. Addition of serum or growth factors to quiescent cells triggered the dissociation of Rb from p55. Ectopic expression of the 24-amino-acid N-terminal end of p55gamma inhibited cell cycle progression, as evidenced by induction of cell growth arrest at the G0/G1 phase, inhibition of DNA synthesis, inhibition of cyclin D and cyclin E promoter activity, and changes in the expression of cell cycle-related proteins. The inhibitory effects of the N-terminal end of p55gamma on cell cycle progression depended on the presence of functional Rb. These data demonstrate for the first time an association of p55gamma with Rb and show that modification of this association can lead to cell cycle arrest.     

Truncated tyrosine kinase B brain-derived neurotrophic factor receptor directs cortical neural stem cells to a glial cell fate by a novel signaling mechanism

During development of the mammalian cerebral cortex neural stem cells (NSC) first generate neurons and subsequently produce glial cells. The mechanism(s) responsible for this developmental shift from neurogenesis to gliogenesis is unknown. Brain-derived neurotrophic factor (BDNF) is believed to play important roles in the development of the mammalian cerebral cortex; it enhances neurogenesis and promotes the differentiation and survival of newly generated neurons. Here, we provide evidence that a truncated form of the BDNF receptor tyrosine kinase B (trkB-t) plays a pivotal role in directing embryonic mouse cortical NSC to a glial cell fate. Expression of trkB-t promotes differentiation of NSC toward astrocytes while inhibiting neurogenesis both in cell culture and in vivo. The mechanism by which trkB-t induces astrocyte genesis is not simply the result of inhibition of full-length receptor with intrinsic tyrosine kinase activity signaling. Instead, binding of BDNF to trkB-t activates a signaling pathway (involving a G-protein and protein kinase C) that induced NSC to become glial progenitors and astrocytes. Thus, the increased expression of trkB-t in the embryonic cerebral cortex that occurs coincident with astrocyte production plays a pivotal role in the developmental transition from neurogenesis to gliogenesis. Our findings suggest a mechanism by which a single factor (BDNF) regulates the production of the two major cell types in the mammalian cerebral cortex.     

Interacting proteins and differences in nuclear transport reveal specific functions for the NAP1 family proteins in plants

Nucleosome assembly protein 1 (NAP1) is conserved from yeast to human and facilitates the in vitro assembly of nucleosomes as a histone chaperone. Inconsistent with their proposed function in the nucleus, however, many NAP1 proteins had been reported to localize in the cytoplasm. We investigated the subcellular localization of tobacco (Nicotiana tabacum) and rice (Oryza sativa) NAP1 family proteins first by identification of interacting partners and by direct examination of the localization of green fluorescent protein-tagged proteins. Through treatment of tobacco cells with leptomycin B and mutagenesis of nuclear export signal, we demonstrated that Nicta;NAP1;1 and Orysa;NAP1;1 shuttle between the cytoplasm and the nucleus. Together with the demonstration that tobacco NAP1 proteins bind histone H2A and H2B, our results support the current model and provide additional evidence that function of NAP1 as histone chaperones appears to be conserved in plants. In addition, we show that tobacco NAP1 proteins interact with tubulin and the mitotic cyclin Nicta;CYCB1;1, suggesting a role for NAP1 in microtubule dynamics. Interestingly, in spite of their high homology with the above NAP1 proteins, the other three tobacco proteins and Orysa;NAP1;2 did not show nucleocytoplasmic shuttling and were localized only in the cytoplasm. Moreover, Orysa;NAP1;3 that lacks a typical nuclear localization signal sequence was localized in both the cytoplasm and the nucleus. Finally, we show that only Orysa;NAP1;3 could be phosphorylated by casein kinase 2alpha in vitro. However, this phosphorylation was not responsible for nuclear import of Orysa;NAP1;3 as being demonstrated through mutagenesis studies. Together, our results provide an important step toward elucidating the molecular mechanism of function of the NAP1 family proteins in plants.