Activation of the phosphatase activity of human cdc25A by a cdk2-cyclin E dependent phosphorylation at the G1/S transition.

Progression through the cell cycle is monitored at two major points: during the G1/S and the G2/M transitions. In most cells, the G2/M transition is regulated by the timing of p34cdc2 dephosphorylation which results in the activation of the kinase activity of the cdc2-cyclin B complex. The timing of p34cdc2 dephosphorylation is determined by the balance between the activity of the kinase that phosphorylates p34cdc2 (wee1 in human cells) and the opposing phosphatase (cdc25C). Both enzymes are regulated and it has been shown that cdc25C is phosphorylated and activated by the cdc2-cyclin B complex. This creates a positive feed-back loop providing a switch used to control the onset of mitosis. Here, we show that another member of the human cdc25 family, cdc25A, undergoes phosphorylation during S phase, resulting in an increase of its phosphatase activity. The phosphorylation of cdc25A is dependent on the activity of the cdc2-cyclin E kinase. Microinjection of anti-cdc25A antibodies into G1 cells blocks entry into S phase. These results indicate that the cdc25A phosphatase is required to enter S phase in human cells and suggest that this enzyme is part of an auto-amplification loop analogous to that described at the G2/M transition. We discuss the nature of the in vivo substrate of the cdc25A phosphatase in S phase and the possible implications for the regulation of S phase entry.     

Transgenic rabbit production with simian immunodeficiency virus-derived lentiviral vector

Transgenic rabbit is the preferred disease model of atherosclerosis, lipoprotein metabolism and cardiovascular diseases since upon introducing genetic mutations of human genes, rabbit models reflect human physiological and pathological states more accurately than mouse models. Beyond that, transgenic rabbits are also used as bioreactors to produce pharmaceutical proteins in their milk. Since in the laboratory rabbit the conventional transgenesis has worked with the same low efficiency in the last twenty five years and truly pluripotent embryonic stem cells are not available to perform targeted mutagenesis, our aim was to adapt lentiviral transgenesis to this species. A simian immunodeficiency virus based replication defective lentiviral vector was used to create transgenic rabbit through perivitelline space injection of fertilized oocytes. The enhanced green fluorescent protein (GFP) gene was placed under the ubiquitous CAG promoter. Transgenic founder rabbits showed mosaic pattern of GFP expression. Transgene integration and expression was revealed in tissues derived from all three primary germ layers. Transgene expression was detected in the developing sperm cells and could get through the germ line without epigenetic silencing, albeit with very low frequency. Our data show for the first time, that lentiviral transgenesis could be a feasible and viable alternative method to create genetically modified laboratory rabbit.     

Genetic mapping of adaptive wing size variation in Drosophila simulans

Many ecologically important traits exhibit latitudinal variation. Body size clines have been described repeatedly in insects across multiple continents, suggesting that similar selective forces are shaping these geographical gradients. It is unknown whether these parallel clinal patterns are controlled by the same or different genetic mechanism(s). We present here, quantitative trait loci (QTL) analysis of wing size variation in Drosophila simulans. Our results show that much of the wing size variation is controlled by a QTL on Chr 3L with relatively minor contribution from other chromosome arms. Comparative analysis of the genomic positions of the QTL indicates that the major QTL on Chr 3 are distinct in D. simulans and D. melanogaster, whereas the QTL on Chr 2R might overlap between species. Our results suggest that parallel evolution of wing size clines could be driven by non-identical genetic mechanisms but in both cases involve a major QTL as well as smaller effects of other genomic regions.     

The oncogenic serine/threonine kinase Pim-1 directly phosphorylates and activates the G2/M specific phosphatase Cdc25C

The proto-oncogene Pim-1 encodes a serine-threonine kinase which is a downstream effector of cytokine signaling and can enhance cell cycle progression by altering the activity of several cell cycle regulators among them the G1 specific inhibitor p21(Waf), the phosphatase Cdc25A and the kinase C-TAK1. Here, we demonstrate by using biochemical assays that Pim-1 can interact with the phosphatase Cdc25C and is able to directly phosphorylate the N-terminal region of the protein. Cdc25C is functionally related to Cdc25A but acts specifically at the G2/M cell cycle transition point and can be inactivated by C-TAK1-mediated phosphorylation. Immuno-fluorescence experiments showed that Pim-1 and Cdc25C co-localize in the cytoplasm of both epithelial and myeloid cells. We find that phosphorylation by Pim-1 enhances the phosphatase activity of Cdc25C and in transfected cells that are arrested in G2/M by bleomycin, Pim-1 can enhance progression into G1. Therefore, we propose that Pim-1 activates Cdc25C by a direct phosphorylation and can thereby assume the function of a positive cell cycle regulator at the G2/M transition.     

Novel SARS-CoV-2 receptors:ASGR1 and KREMEN1

The interaction of the SARS-CoV-2 spike protein with the cellular receptor ACE2 is believed to be essential for viral entry into host cells.in a recent paper pu...     

Opposing effects of nitric oxide on different connexins expressed in the vascular system

Gap junctions--clusters of intercellular channels built by connexins (Cx)--are thought to be important for vascular cell functions such as differentiation, control of tone, or growth. In the vascular system, gap junctions can be formed by four different connexins (Cx37, Cx40, Cx43 and Cx45). The permeability of these connexin-formed gap junctions determines the amount of intercellular coupling and can be modulated by several vasoactive substances such as prostacyclin or nitric oxide (NO). We demonstrate here that NO has specific effects on certain connexins. Using two different techniques--injection of a fluorescent dye in single cells as well as detection of the de novo formation of gap junctions by a flow cytometry based technique--we found that NO decreases the functional coupling in Cx37 containing gap junctions whereas it increases the de novo formation of gap junctions containing Cx40. We conclude that NO, in addition to its known vasomotor effects, has a novel role in controlling intercellular coupling resulting in opposing effects depending on the specific connexin expressed in the cells.