Dynamics of gene differentiation between incompletely isolated populations of unequal sizes

The progress of gene differentiation between two populations of unequal sizes is studied by taking into account the effects of mutation and migration. Explicit formulae for the eventual rate of approach to equilibrium of the probabilities of identity of genes by descent within and between populations are worked out for the case of small migration. Formulae for the equilibrium values of identity probabilities are also given for some special cases. It is shown that in the case of large migration the Nei—Feldman formulae for the temporal changes and equilibrium values of identity probabilities approximately hold, unless the sizes of the two populations are extremely different. The theories developed are applied to study the evolution of cave fish populations in Astyanax mexicanus. The approximate time after divergence between the cave and river populations of this fish has been estimated to be 525,000–710,000 years, which agrees well with the geological data on cave formation.     

Cabozantinib inhibits AXL- and MET-dependent cancer cell migration induced by growth-arrest-specific 6 and hepatocyte growth factor

Cabozantinib is known as an inhibitor of receptor tyrosine kinases mainly targeting AXL receptor tyrosine kinase (AXL), MET proto-oncogene-encoded receptor tyrosine kinase (MET), and vascular endothelial growth factor receptor 2. Growth arrest-specific 6 (GAS6) and hepatocyte growth factor (HGF), the natural ligands of AXL and MET, respectively, are associated with the induction of cancer cell proliferation or metastasis. Currently, it is still unclear how cabozantinib regulates cancer cell migration and invasion by inhibiting AXL and MET. This study was conducted to investigate the mechanism underlying the anti-cancer effects of cabozantinib through regulation of AXL and MET signaling.The results of Boyden chamber assays showed that cancer cell migration was induced by GAS6 and HGF in SKOV3 cells in serum-free medium. Combinatorial treatment with GAS6 and HGF exerted an additive effect on cell migration. Furthermore, we examined the role of AXL and MET signaling in cell migration. Short interfering RNA targeting AXL and MET inhibited GAS6- and HGF-induced migration, respectively. Double knockdown of AXL and MET completely suppressed cell migration induced by combination treatment with GAS6 and HGF compared to AXL or MET inhibition alone. Finally, we investigated the effects of cabozantinib on cell migration and invasion. Cabozantinib inhibited AXL and MET phosphorylation and downregulated the downstream mediators, phosphorylated SRC in the presence of both GAS6 and HGF in SKOV3 cells. The cell migration and invasion induced by combined GAS6 and HGF treatment were suppressed by cabozantinib, but not by capmatinib, a selective MET inhibitor.Our data indicate that the GAS6-AXL and HGF-MET signal pathways markedly contribute to cancer cell migration and invasion in an independent manner, suggesting that simultaneous inhibition of these two pathways contributes to the anti-cancer effects of cabozantinib.     

Organic anion transporter 1 (OAT1/SLC22A6) enhances bioluminescence based on d-luciferin–luciferase reaction in living cells by facilitating the intracellular accumulation of d-luciferin

Bioluminescence (BL) imaging based on d-luciferin (d-luc)–luciferase reaction allows noninvasive and real-time monitoring of luciferase-expressing cells. Because BL intensity depends on photons generated through the d-luc–luciferase reaction, an approach to increase intracellular levels of d-luc could improve the detection sensitivity. In the present study, we showed that organic anion transporter 1 (OAT1) is useful, as a d-luc transporter, in boosting the BL intensity in luciferase-expressing cells. Functional screening of several transporters showed that the expression of OAT1 in HEK293?cells stably expressing Pyrearinus termitilluminans luciferase (HEK293/eLuc) markedly enhanced BL intensity in the presence of d-luc. When OAT1 was transiently expressed in HEK293?cells, intracellular accumulation of d-luc was higher than that in control cells, and the specific d-luc uptake mediated by OAT1 was saturable with a Michaelis constant (K_m) of 0.23?μM. The interaction between OAT1 and d-luc was verified using 6-carboxyfluorescein, a typical substrate of OAT1, which showed that d-luc inhibited the uptake of 6-carboxyfluorescein mediated by OAT1. BL intensity was concentration-dependent at steady states in HEK293/eLuc cells stably expressing OAT1, and followed Michaelis–Menten kinetics with an apparent K_m of 0.36?μM. In addition, the enhanced BL was significantly inhibited by OAT1-specific inhibitors. Thus, OAT1-mediated transport of d-luc could be a rate-limiting step in the d-luc–luciferase reaction. Furthermore, we found that expressing OAT1 in HEK293/eLuc cells implanted subcutaneously in mice also significantly increased the BL after intraperitoneal injection of d-luc. Our findings suggest that because OAT1 is capable of transporting d-luc, it can also be used to improve visualization and monitoring of luciferase-expressing cells.     

Identification of Brassinosteroids That Appear to Be Derived from Campesterol and Cholesterol in Tomato Shoots

To obtain information about the biosynthesis of brassinosteroids(BRs) in tomato shoots, we examined endogenous BRs by gas chromatography-massspectrometry. We identified two C²⁸ BRs, namely, castasteroneand 6-deoxocastasterone, and a C²⁷ BR, 28-norcastasterone. Ourfindings suggest that the major BRs in tomato are derived fromcampesterol and cholesterol. ⁴Present address: National Research Institute of Vegetables,Ornamental Plants and Tea, 360 Kusawa, Ano, Mie, 514-23 Japan.     

Polymorphism and evolution of influenza A virus genes

The nucleotide sequences of four genes of the influenza A virus (nonstructural protein, matrix protein, and a few subtypes of hemagglutinin and neuraminidase) are compiled for a large number of strains isolated from various locations and years, and the evolutionary relationship of the sequences is investigated. It is shown that all of these genes or subtypes are highly polymorphic and that the polymorphic sequences (alleles) are subject to rapid turnover in the population, their average age being much less than that of higher organisms. Phylogenetic analysis suggests that most polymorphic sequences within a subtype or a gene appeared during the last 80 years and that the divergence among the subtypes of hemagglutinin genes might have occurred during the last 300 years. The high degree of polymorphism in this RNA virus is caused by an extremely high rate of mutation, estimated to be 0.01/nucleotide site/year. Despite the high rate of mutation, most influenza virus genes are apparently subject to purifying selection, and the rate of nucleotide substitution is substantially lower than the mutation rate. There is considerable variation in the substitution rate among different genes, and the rate seems to be lower in nonhuman viral strains than in human strains. The difference might be responsible for the so-called freezing effect in some viral strains.