Mouse gastrulation: the formation of a mammalian body plan

The process of gastrulation is a pivotal step in the formation of the vertebrate body plan. The primary function of gastrulation is the correct placement of precursor tissues for subsequent morphogenesis. There is now mounting evidence that the body plan is established through inductive interactions between germ layer tissues and by the global patterning activity emanating from embryonic organizers. An increasing number of mouse mutants have been described that have gastrulation defects, providing important insights into the molecular mechanisms that regulate this complex process. In this review, we explore the mouse embryo before and during gastrulation, highlighting its similarities with other vertebrate embryos and its unique characteristics.     

Superfluid effects at the onset of convection in3He-superfluid-4He mixtures

The equations of motion for convection in dilute³He-superfluid-⁴He mixtures are the same as those for convection in a conventional pure fluid with the addition of several correction terms. Fetter has considered, for a horizontally infinite layer with realistic boundary conditions, the effect of these corrections on the critical Rayleigh number,R _c . The results are a perturbation expansion forR _c to lowest order in three perturbation terms, ₁ , ₂ , ₃ . In order to make a comparison with recent precise experiments which have yieldedR _c as a function of the layer heightd, we have carried out several calculations. First we show that the analysis can be recast as an expansion in inverse powers ofd ². We then carry out a complete expansion toO(d ^–6). Up toO(d ^–4), the expansion involves only the ratio ( ₀ /d) where ₀ is a length scale which is intrinsic to superfluid mixtures. We consider the effect of the superfluid perturbations on both the critical Rayleigh numbers and wavevectors. These are shifted very little as long as ₀ /d is small; the crossover from large to small occurs for ₀ /d0.1. We also solve a simplified version of the stability problem which contains the dominant superfluid effect. The simplified problem is Hermitian, and is therefore amenable to an exact solution. A comparison with experimental data forR _c and the simplified model shows excellent agreement with the calculations.     

Assimilation of the knowledgeable newcomer under conditions of group success and failure.

"It was proposed that a new member may be perceived as either a resource or as an unwelcome source of disruption, depending upon the needs of the group… . [and] it was hypothesized that a newcomer is accepted more readily by a group with a history of failure than by a successful group." Hypotheses supported and meaning of results discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thermodynamic properties of liquid3He-4He mixtures near the tricritical point. I. Vapor pressure measurements and their thermodynamic analysis

Sensitive vapor pressure (P _sat) measurements of ³ He- ⁴ He mixtures by means of a low-temperature strain gauge are described over the temperature range 0.5–1.5 K and the range 0.4<X<0.85, whereX is the ³ He mole fraction in the liquid phase. The vapor pressure cell is flat, with a height of only 2 mm, in order to reduce concentration gradients near the tricritical point. The pressure-sensitive device, which resolves changes of about 5×10 ^–8 atm, is described, and its advantages over a conventional manometer system are discussed. Data taken successively on mixtures of small mole fraction difference are used to locate the phase separation boundary in theT-X plane and also the lambda line from a change in (P _sat/T) _x at these transitions. The limiting slopes (dT/dX) and (dT/dX) of the phase separation curve and the lambda line in the vicinity of their junction point, the tricritical point, are presented and compared with previous work. From the vapor pressure data, the concentration susceptibility (X/) _T,P was obtained. Here = ₃ – ₄ is the chemical potential difference of the respective isotopic components ³ He and ⁴ He. It is shown that (X/) _t diverges as the tricritical point is approached along various paths in theT-X plane, and the relevant tricritical exponents are presented. The weak divergence of (X/) _T along the lambda line predicted from the postulates of Griffiths and Wheeler could not be detected and it is believed that such divergence has to occur in a temperature interval that is far too small to be resolved with present-day techniques. Furthermore, gravity effects might well prevent observation of the weak divergence. The lambda transition is well evidenced by a distinct shoulder in a plot of (X/) _T at constantX as a function ofT. This shoulder becomes smaller and gradually gets topped by a peak asX decreases from the tricritical mole fractionX _t . From a combination of vapor pressure and calorimetric data the chemical potential difference [(X, T)- _t ] is calculated between 0.78 and 1.22 K. Here _t is the value at the tricritical point. From this tabulation the critical line and its slope (d/dT) are obtained and compared with previous values based on calorimetric experiments only and with calculations based on the excess chemical potentials ₃ ^E and ₄ ^E derived from saturated vapor pressure data.Work supported by a Grant from the National Science Foundation.     

Critical Rayleigh numbers for cryogenic experiments

We give critical Rayleigh numbers, R_c, and the corresponding critical wavevectors, a_c, for the onset of Rayleigh-Bénard convection for thermal conditions on the horizontal boundaries that model physical experiments, particularly those carried out at low temperatures with liquid helium. We assume that a fluid layer, satisfying the Boussinesq approximation, is bounded above and below by rigid plates with finite, nonzero vertical thicknesses and finite thermal conductivities. The effect of sidewalls on R_c is not likely to be important for many experiments and so is not considered here; specifically, we assume a horizontally infinite layer. At the top of the top plate and the bottom of the bottom plate, we consider boundary conditions for which a linear combination of the convective temperature field and its vertical derivative vanishes. For these boundary conditions, the growth rates of the linear stability problem are necessarily real. We find that R_c only deviates significantly from 1708 and a_c only deviates significantly from 3.11, when the thermal conductivity of the fluid is comparable to or larger than that of the boundaries, or when the plates are exceptionally thin. In particular a fixed heat flux applied to highly conducting plates (a configuration frequently used in cryogenic experiments) does not cause R_c to vary much from the standard value, 1708.     

Electron-beam treatment of aromatic hydrocarbons that can be air-stripped from contaminated groundwater. 1. Model studies in aqueous solution

As a model for the electron-beam degradation of volatile aromatics (benzene, toluene, ethylbenzene, xylenes, BTEX) in groundwater strip gas, to be reported in Part 2, the gamma-radiolysis of benzene has been studied in aqueous solutions. Addition of *OH to the aromatic ring gives rise to hydroxycyclohexadienyl radicals which either dimerize or disproportionate. The various dimers undergo acid-catalyzed water elimination yielding biphenyl. Phenol is formed upon disproportionation directly, but also via dihydroxycyclohexadiene which subsequently undergoes acid-catalyzed water elimination. Co-radiolysis of benzene with nitrite generates *NO2 in addition to the hydroxycyclohexadienyl radical. These not only interact with one another (product: nitrobenzene via nitro-hydroxycyclohexadienes) but the *NO2 radical is also capable of abstracting cyclohexadienylic hydrogens. This reaction leads to the formation of 2- and 4-nitrophenol and to further nitrated products that were not identified. These are suggested to be formed in an analogous reaction of *NO2 with the hydroxycylohexadienyl dimers. The effect of O2 on these reactions and the relevance for the gas-phase radiolysis of BTEX is discussed.     

Spontaneous calcification of arteries and cartilage in mice lacking matrix GLA protein

Calcification of the extracellular matrix (ECM) can be physiological or pathological. Physiological calcification occurs in bone when the soft ECM is converted into a rigid material capable of sustaining mechanical force; pathological calcification can occur in arteries and cartilage and other soft tissues. No molecular determinant regulating ECM calcification has yet been identified. A candidate molecule is matrix GLA protein (Mgp), a mineral-binding ECM protein synthesized by vascular smooth-muscle cells and chondrocytes, two cell types that produce an uncalcified ECM. Mice that lack Mgp develop to term but die within two months as a result of arterial calcification which leads to blood-vessel rupture. Chondrocytes that elaborate a typical cartilage matrix can be seen in the affected arteries. Mgp-deficient mice additionally exhibit inappropriate calcification of various cartilages, including the growth plate, which eventually leads to short stature, osteopenia and fractures. These results indicate that ECM calcification must be actively inhibited in soft tissues. To our knowledge, Mgp is the first inhibitor of calcification of arteries and cartilage to be characterized in vivo.     

Influence of diet on nipple aspirate fluid production and estrogen levels

One possible mechanism how nutritional factors may affect breast cancer risk is through an influence on estrogen levels. Nipple aspirate fluid (NAF) is thought to provide a more direct insight into hormonal influences on breast tissue than serum. The ability to produce NAF may be an indicator of breast cancer risk. The current analysis was conducted as part of a soy trial in 92 premenopausal women and evaluated the relation of usual dietary intake with NAF volume and the most predominant steroidal estrogens in NAF and serum at baseline. Estradiol (E(2)) and estrone sulfate (E(1)S) were assessed in NAF and E(2), estrone (E(1)), and E(1)S, in serum using highly sensitive radioimmunoassays. The statistical analysis applied multivariate, log-linear regression models. Intake of saturated fat and cheese (p = 0.06 for both) indicated a positive trend with NAF volume whereas isoflavonoid and soy consumption suggested inverse associations (p = 0.01 and p = 0.08). For estrogens in NAF, total fat and monounsaturated fat intake was positively associated with E(2) (p = 0.05 and p = 0.02) and in serum, alcohol intake was associated with higher E(1)S levels (p = 0.02). These findings suggest a weak influence of dietary composition on NAF production and estrogen levels in serum and NAF.