Molecular organization of theD-Qa region oft-haplotypes suggests that recombination is an important mechanism for generating genetic diversity of the major histocompatibility complex

We have determined the molecular maps of theH-2D andQa regions of thet-complex haplotypest ^l2 andt ^w5 by chromosomal walking. Analysis with class I probes and other probes unique to theH-2D:Qa subregion indicates that the class I gene organization oft ¹² is:D1-D2-Q1-Q2-Q3-Qx-Q4-Q5-Q10, while that oft ^w5 is:D1-D2-Q1-Q2-Q4-Q5-Q10. Thus, the absence of theQ6-Q9 genes suggested previously int-haplotypes was confirmed. A comparison of the molecular maps of thet ¹² andt ^w5 chromosomes revealed an extremely mosaic pattern of diversity: The regions betweenD1 andD2, and betweenQ4 andQ10, are very similar in both chromosomes. However, theirQ1 toQ3 regions are strikingly different. Further comparisons of wild-type chromosomes and additionalt-haplotypes by molecular mapping and genomic Southern blot hybridization with probes to theQ1-Q3 region showed a high level of polymorphism among both wild-type chromosomes and amongt-haplotypes. The characteristics of the polymorphisms suggest that recombination may play an important role in generating this genetic diversity. Furthermore, recombination between wild-type andt-haplotype chromosomes may be involved.     

Comparison of mammary tumorigenesis between litters in relation to mammary tumor virus antigenic expression in the milk of C3H/He mice

As a possible step to estimate the relationship between mammary tumor virus (MTV) and mammary tumorigenesis in mice, MTV antigenic expression in mother's milk and spontaneous mammary tumorigenesis in their daughters were compared between the 1st, the 2nd and the 3rd litters of the highly inbred strains of C3H/He mice with low mammary tumor incidence. While MTV antigenic expression was detected in all undiluted samples at each litter by immunodiffusion test, the amount of antigen as measured by the single radial immunodiffusion method was increased with increasing litter numbers. On the other hand, the development of preneoplastic mammary hyperplastic alveolar nodules was different little between litters and mammary tumor incidence by 13 months of age was very low with no difference in all litters. The pattern of estrous cycles and plasma prolactin level were also similar in each litter. The results suggest that spontaneous mammary tumorigenesis in mice is not always affected quantitatively by the amount of MTV when endocrine and genetical conditions are similar.     

Pertussis toxin-sensitive and insensitive intracellular signalling pathways in undifferentiated 3T3-L1 cells stimulated by insulin converge with phosphatidylinositol 3-kinase upstream of the Ras mitogen-activated protein kinase cascade.

We have previously reported that pertussis toxin (PTX)-sensitive GTP binding protein (G-protein) and phosphatidylinositol 3-kinase (PI 3-K) are involved in adipocyte differentiation of 3T3-L1 cells induced by insulin/dexamethasone/methylisobutyl xanthine. The aim of this study was to examine the effect of PTX on the tyrosine kinase cascade stimulated by insulin acting through insulin-like growth factor-I (IGF-I) receptors in undifferentiated 3T3-L1 cells. A high level of mitogen-activated protein kinase (MAPK) activation was sustained for up to 4 h after insulin treatment, and mobility shifted and tyrosine phosphorylated MAPK was also detected. MAPK kinase activity measured by the incorporation of 32P into kinase-negative recombinant MAPK was enhanced by insulin treatment. We previously discovered that insulin activates Ras and that this is mediated by wortmannin-sensitive PI 3-K. Tyrosine-phosphorylation of IRS-1 and Shc also occurred in response to insulin. Subsequently, we investigated the effects of PTX on the activation of these proteins by insulin. Interestingly, treating 3T3-L1 cells with PTX attenuates the activation by insulin of both the Ras-MAPK cascade and PI 3-K. In contrast, neither tyrosine-phosphorylation of IRS-1 and Shc nor the interaction between IRS-1 and PI 3-K is sensitive to PTX. However, activation of the Ras-MAPK cascade and tyrosine-phosphorylation of Shc by epidermal growth factor are insensitive to PTX. These results indicate that there is another pathway which regulates PI 3-K and Ras-MAPK, independent of the pathway mediated by IGF-I receptor kinase. These findings suggest that in 3T3-L1 fibroblasts, PTX-sensitive G-proteins cross-talk with the Ras-MAPK pathway via PI 3-K by insulin acting via IGF-I receptors.     

Endothelin/endothelin-B receptor signals regulate ventricle-directed interkinetic nuclear migration of cerebral cortical neural progenitors

We determined the expression profile of ～300 G protein-coupled receptors (GPCRs) in embryonic cortical neural progenitor cells (NPCs) and identified a number of highly expressed GPCRs, among which endothelin-B receptor (ET(B)-R) was expressed at the highest level. We also revealed that endothelins (ETs) were predominantly expressed in CD31-positive endothelial cells of the embryonic cerebral cortex. Activation of ET(B)-R induced NPC assembly in vitro by promoting fibronectin-dependent-motility and N-cadherin-associated cell contact. NPC assembly also required a Rho-family GTPase(s) and phosphatidylinositol-3-kinase. In the embryonic cerebral cortex, a specific ET(B)-R agonist, IRL-1620, accelerated interkinetic nuclear migration (INM) of NPCs toward the ventricular wall (VW) ex vivo. Conversely, a specific ET(B)-R antagonist, BQ788, slowed INM, thereby inducing mislocalization of phospho-histone H3-positive M-phase nuclei in the ventricular zone (VZ) and decreasing the number of Tuj1-positive newborn neurons. Our results suggest that ET(B)-R-mediated assembly signals drive INM that precedes neurogenesis.     

Modeling myosin-dependent rearrangement and force generation in an actomyosin network

Actomyosin contractility is a major force-generating mechanism that drives rearrangement of actomyosin networks; it is fundamental to cellular functions such as cellular reshaping and movement. Thus, to clarify the mechanochemical foundation of the emergence of cellular functions, understanding the relationship between actomyosin contractility and rearrangement of actomyosin networks is crucial. For this purpose, in this study, we present a new particulate-based model for simulating the motions of actin, non-muscle myosin II, and α‐actinin. To confirm the model's validity, we successfully simulated sliding and bending motions of actomyosin filaments, which are observed as fundamental behaviors in dynamic rearrangement of actomyosin networks in migrating keratocytes. Next, we simulated the dynamic rearrangement of actomyosin networks. Our simulation results indicate that an increase in the density fraction of myosin induces a higher-order structural transition of actomyosin filaments from networks to bundles, in addition to increasing the force generated by actomyosin filaments in the network. We compare our simulation results with experimental results and confirm that actomyosin bundles bridging focal adhesions and the characteristics of myosin-dependent rearrangement of actomyosin networks agree qualitatively with those observed experimentally.     

Genomic organization and genomic structural rearrangements of Sphingobium japonicum UT26, an archetypal γ-hexachlorocyclohexane-degrading bacterium

The complete genome sequencing of a γ-hexachlorocyclohexane-degrading strain, Sphingobium japonicum UT26, revealed that the genome consists of two circular chromosomes [with sizes of 3.5 Mb (Chr1) and 682kb (Chr2)], a 191-kb large plasmid (pCHQ1), and two small plasmids with sizes of 32 and 5kb. The lin genes are dispersed on Chr1, Chr2, and pCHQ1. Comparison of the UT26 genome with those of other sphingomonad strains demonstrated that the "specific"lin genes for conversion of γ-HCH to β-ketoadipate (linA, linB, linC, linRED, and linF) are located on the DNA regions unique to the UT26 genome, suggesting the acquisition of these lin genes by horizontal transfer events. On the other hand, linGHIJ and linKLMN are located on the regions conserved in the genomes of sphingomonads, suggesting that the linGHIJ-encoded β-ketoadipate pathway and the LinKLMN-type ABC transporter system are involved in core functions of sphingomonads. Based on these results, we propose a hypothesis that UT26 was created by recruiting the specific lin genes into a strain having core functions of sphingomonads. Most of the specific lin genes in UT26 are associated with IS6100. Our analysis of spontaneous linA-, linC-, and linRED-deletion mutants of UT26 revealed the involvement of IS6100 in their deduced genome rearrangements. These facts strongly suggest that IS6100 plays important roles both in the dissemination of the specific lin genes and in the genome rearrangements.