The Pristionchus pacificus mab-5 gene is involved in the regulation of ventral epidermal cell fates

One system that can be used to study the evolution of gene function is the nematode vulva. In Caenorhabditis elegans, the vulva is formed from three of the six multipotent precursors P(3-8).p. Comparison of vulval development between C. elegans and Pristionchus pacificus has revealed that, during evolution, there have been changes in the specification of cell fate for certain vulval cells. For example, the cell P8.p is a vulval precursor cell (VPC) in C. elegans, but is incompetent to adopt vulval fate in P. pacificus We have fate specification and have isolated P. pacificus mutants with a second vulva-like structure in the posterior region resulting from the ectopic differentiation of P8.p Genetic and molecular analysis indicated that point mutations in the Hox-cluster gene mab-5 of P. pacificus cause this multivulval phenotype. Further cell ablation studies revealed that the differentiation of P8.p is independent of gonadal signaling. In C. elegans, mab-5 also acts in P8.p specification, but mab-5 mutant animals do not develop differs between species, indicating that alterations in the intrinsic properties of P8.p and corresponding changes in the functional specificity of mab-5 have occurred during evolution.     

Mash1 and neurogenin1 expression patterns define complementary domains of neuroepithelium in the developing CNS and are correlated with regions expressing notch ligands

Genetic studies in Drosophila and in vertebrates have implicated basic helix-loop-helix (bHLH) genes in neuronal fate determination and cell type specification. We have compared directly the expression of Mash1 and neurogenin1 (ngn1), two bHLH genes that are expressed specifically at early stages of neurogenesis. In the PNS these genes are expressed in complementary autonomic and sensory lineages. In the CNS in situ hybridization to serial sections and double-labeling experiments indicate that Mash1 and ngn1 are expressed in adjacent and nonoverlapping regions of the neuroepithelium that correspond to future functionally distinct areas of the brain. We also showed that in the PNS several other bHLH genes exhibit similar lineal restriction, as do ngn1 and Mash1, suggesting that complementary cascades of bHLH factors are involved in PNS development. Finally, we found that there is a close association between expression of ngn1 and Mash1 and that of two Notch ligands. These observations suggest a basic plan for vertebrate neurogenesis whereby regionalization of the neuroepithelium is followed by activation of a relatively small number of bHLH genes, which are used repeatedly in complementary domains to promote neural determination and differentiation.     

Peierls-Nabarro hardening in the presence of point obstacles

In light of the controversy that has existed between proponents of Peierls-Nabarro hardening and dispersed barrier hardening with regard to possible low temperature deformation mechanisms in bee and hep metals, this paper examines the effect of point obstacles on Peierls-Nabarro hardening. The statics of double kink nucleation over Peierls barrier on finite dislocation segments are studied in detail. Point obstacles such as interstitial impurity atoms are considered to limit the length of the dislocation segments. Adopting the rate theory approach, temperature dependence of the yield stress is then investigated as a function of the concentration of point obstacles. It is found that point obstacles have little or no effect on double kink nucleation processes, when the applied stress is near the Peierls stress or at low test temperatures. At lower applied stresses or at higher test temperatures, the present results are significantly different from predictions of the Dorn-Rajnak calculation. In the present theory, the applied stress on the dislocation, τ, is found to be finite and independent of test temperature in dilute solid solutions at elevated temperatures where the Dorn-Rajnak theory predicts vanishing τ. This apparent “athermal” component of τ increases linearly with the concentration of point obstacles, whereas temperature dependent part of τ decreases. These predictions are consistent with experimental observations on iron-base alloys.     

Mechanism of Work-hardening for Austenitic Manganese Steel under Non-severe Impact Loading Conditions

The effect of C,Mn and heat-treatment onwork-hardening of austenitic Mn steel and thework-hardening mechanism have been investigatedunder non-severe impact loading condition.Theresults show that the ability of work-hardening in-creases with the increase of C and aging tempera-ture but decreases with Mn.The work-hardeningwith high austenitic stability results mainly fromdislocations,and that with low austenitic stabilityresults mainly from combined effects of strain-in-duced martensite and high density of dislocationsunder non-severe impact loading conditions.Thewear resistance of medium manganese steel (Mn7)is 1.64-2.46 times that of Hadfield steel (Mnl3).     

Synthesis of bulk and reinforced

Preforms of nickel powder or nickel/alumina powder blends were infiltrated with molten aluminum to produce nickel aluminides. Application of a pressure of 3.6 and 6.9 MPa on the melt allowed infiltration of preforms with nickel powder particles between 5 and 15 μm in diameter, which could not be infiltrated under the sole action of capillary forces. By varying the initial preform temperature from 705 °C to 280 °C, the diameter of nickel powder particles from 15 to 150 μm, and the volume fraction of alumina from 0 to 34 vol pct, pressure-infiltrated samples with large variations in the extent of reaction between nickel and aluminum were pro- duced. The range of microstructure extended from fully reacted nickel aluminide to essentially unreacted nickel/aluminum samples containing low levels of final porosity. In particular, it was found that reducing the initial preform temperature below the melting point of aluminum results in a reduction of the rate and extent of aluminide formation, allowing, in turn, reduction of macrosegregation within the resulting infiltrated material. Formerly Research Assistant, Department of Materials Science and Formerly Research Assistant, Department of Materials Science and     

Topographic-anatomic study of tissue transplants of the inguinal region

We performed 25 fresh cadaver dissections to describe the anatomy of the superficial and deep circumflex iliac artery and the superficial inferior epigastric artery to determine how they could least to used as donor vessels for the free transfer of groin flaps and living iliac bone. With injection of ink the capillary region of these vessels was stained in (iliac crest) bone, the internal oblique muscle and skin of the groin and thigh. The superficial and deep circumflex iliac artery were shown to be the main supply vessels of the groin and thigh and could be found in 96%-100% of cases. The venous drainage of this region followed from a superficial system (superficial circumflex iliac veins) and a deep venous system (Vv. comitantes accompanying arterial branches). Both venous systems could always be found. The superficial circumflex iliac artery was shown to only supply the skin and was the main donor vessel to the skin and soft tissue transplants. The deep circumflex iliac artery supplied the pelvic bone, the internal oblique muscle and a small constant area of skin above the iliac crest. Bone, muscle and bone, muscle and skin transplants could be obtained with this donor vessel, with enlargement of the skin area possible by combining two arterial branches combined in one transplant. With an average vessel diameter of 1.5 mm (superficial circumflex iliac artery) and 3 mm (deep circumflex iliac artery) both vessels could be used satisfactorily for microvascular transplantation. Different tissues including muscle, bone and skin could be obtained in adequate amounts to replace composite defects in the upper aerodigestive tract.     

The burnt-out chairman.

Discusses what it means to be a department chairperson, based on the author's 6.5 yrs of experience in this position. The frustrations and compensations of the job are considered. It is noted that administrative concerns come to replace concerns about the direction of the department. (PsycINFO Database Record (c) 2010 APA, all rights reserved)