Triangular nanoperforation and band engineering of InGaAs quantum wells: a lithographic route toward Dirac cones in III-V semiconductors.

The design of two-dimensional periodic structures at the nanoscale has renewed attention for band structure engineering. Here, we investigate the nanoperforation of InGaAs quantum wells epitaxially grown on InP substrates using high-resolution e-beam lithography and highly plasma based dry etching. We report on the fabrication of a honeycomb structure with an effective lattice constant down to 23 nm by realising triangular antidot lattice with an ultimate periodicity of 40 nm in a 10 nm thick InGaAs quantum well on a p-type InP. The quality of the honeycomb structures is discussed in detail, and calculations show the possibility to measure Dirac physics in these type of samples. Based on the statistical analysis of the fluctuations in pore size and periodicity, calculations of the band structure are performed to assess the robustness of the Dirac cones with respect to distortions of the honeycomb lattice.

Notch/Delta expression in the developing mouse lung.

Factors controlling the differentiation of the multipotent embryonic lung endoderm and mesoderm are poorly understood. Recent evidence that Delta-like 1 (Dll1) and other genes in the Notch/Delta signaling pathway are expressed in the embryonic mouse lung suggests that this pathway is important for cell fate decisions and/or the differentiation of lung cell types. Here, we report the localization of transcripts of several genes encoding members of the Notch/Delta pathway in the early mouse lung. Most genes are expressed in specific populations and so may contribute to cell diversification.

Severe limb defects in Hypodactyly mice result from the expression of a novel, mutant HOXA13 protein.

Hypodactyly (Hoxa13(Hd)) mice have a 50-bp deletion in the coding region of exon 1 of the Hoxa13 gene and have more severe limb defects than mice with an engineered deletion of the entire gene (Hoxa13(-/-)). Increased cell death is observed in the autopod of Hoxa13(Hd/Hd) but not Hoxa13(-/-) limb buds. In addition, compound heterozygotes for one Hd allele and a Hoxa13(-) allele have a more severe limb phenotype than mice homozygous for the engineered null allele, suggesting a dominant-negative effect of the Hd mutation. The Hoxa13(Hd) deletion does not interfere with steady-state mRNA levels; however, its consequences on translation are unknown. In this paper, we characterize the Hoxa13 transcription initiation site in limbs and determine the initiator methionine of HOXA13. We show that the Hoxa13(Hd) deletion results in a translational frame shift that leads to the loss of wild-type HOXA13 protein and the simultaneous production of a novel, stable protein in the limb buds of mutant mice. The mutant Hd protein (HOXA13(Hd)) consists of the first 25 amino acids of wild-type HOXA13 sequence, followed by 275 amino acids of arginine- and lysine-rich, novel sequence, and lacks the homeodomain. Like wild-type HOXA13, HOXA13(Hd) is localized to the nucleus in transfected COS-7 cells, perhaps mediated by the arginine- and lysine-rich peptide sequences created by the translational frame shift. To determine whether HOXA13(Hd) could alter limb morphogenesis, we misexpressed the mutant mRNA throughout the developing limb bud using a Prx-1 promoter-Hd gene construct in transgenic mice. Three of 15 transgenic founder animals displayed reduction or absence of proximal and distal limb structures. We propose that the expression of HOXA13(Hd) plays a role in the profound failure of digit formation in Hoxa13(Hd/Hd) mice and explains the morphologic differences between these two Hoxa13 alleles.

Infertility in adult hypodactyly mice is associated with hypoplasia of distal reproductive structures.

Hypodactyly (Hoxa13(Hd)) mice have a 50-base-pair deletion in Hoxa13, and rare surviving homozygotes of both sexes are infertile. Heterozygous mutant mice are fertile; however, Hoxa13(Hd/+) females exhibit an anterior transformation of cervical tissue to a uterine stromal phenotype that is accentuated in the homozygote and occasionally includes uterine-specific glands in the transformed cervical region. The columnar-to-squamosal epithelial transition that characterizes mature cervical-vaginal tissue is positioned within uterine-like stroma rather than cervical tissue in these mutants, suggesting that this postnatal developmental transition occurs independent of the underlying stromal characteristics. Hoxa13(Hd/Hd) adult females produce apparently functional germ cells as determined by superovulation and ovarian histology, but they exhibit profound hypoplasia of the cervix and vaginal cavity. Using whole-mount in situ hybridization, we localized Hoxa13 expression to the cervical and vaginal tissues, consistent with the observed defects. In Hoxa13(Hd/Hd) males, the penian bone is severely hypoplastic and misshapen. The penian bone develops by a combination of endochondral and intramembranous ossification, but the defects observed in Hoxa13(Hd/Hd) males are limited to the region of endochondral bone formation. Our results indicate that infertility in Hypodactyly mutants is related to hypoplasia of the vaginal cavity and cervix in females and deficiency of the os penis in males.

Altered Hox expression and increased cell death distinguish Hypodactyly from Hoxa13 null mice.

Hypodactyly (Hoxa13Hd) mice have a small deletion within the coding sequence of Hoxa13 and a limb phenotype that is more severe than that of mice with an engineered null allele of Hoxa13. We used whole-mount in situ hybridization, Nile blue sulfate staining and genetic crosses to determine the basis for the phenotypic differences between these two mutants. Expression of Hoxd13 was unaffected in Hoxa13-/- mice, but its domain was reduced at the anterior and posterior margins of the autopod in Hoxa13Hd/Hd limb buds. The maturation of Hoxd11 expression was delayed and expression of Hoxa11 failed to become restricted to the autopod/zeugopod junction in both Hoxa13Hd/Hd and Hoxa13-/- limb buds compared to wild-type mice. Fgf8 expression was normal in both Hoxa13Hd/Hd and Hoxa13-/- mice throughout limb development. A dramatic increase in cell death was observed in limb bud mesenchyme of Hoxa13Hd/Hd mice as early as E11.5 but not in mice homozygous for the null allele. Genetic background was excluded as the basisforthe phenotypic differences. Compound heterozygotes (Hoxa13-/Hd) displayed an intermediate phenotype relative to both homozygotes suggesting that Hoxa13Hd has an effect on the development of the autopod beyond that which may result from a loss of HOXA13 protein. These results showthat Hoxa13Hd has a negative effect on the survival of the mesenchyme in the autopod, unlike the Hoxa13 null mutation, that cannot be explained by a failure of the AER to express Fgfs. In addition, at least one target of HOXA13 may be Hoxa11.

The molecular basis of hypodactyly (Hd): a deletion in Hoxa 13 leads to arrest of digital arch formation.

Hypodactyly (Hd) is a semidominant mutation in mice that maps in a genetic interval overlapping the Hoxa cluster. The profound deficiency of digital arch structures in Hd/Hd mice is consistent with a defect in a gene activated late in limb morphogenesis. We have determined the structure of the Hoxa13 gene and describe a 50-base pair deletion in the first exon of the Hd allele that probably arose from unequal recombination or misalignment between triplet repeats. It is predicted that no Hoxa13 protein is made from Hd mRNA. The hypodactyly limb phenotype is similar to that of Hoxd13-deficient mice in sharing defects along multiple axes and alterations in cartilage maturation; however, the overall effects on digital arch formation are more severe in Hd/Hd mice. Our results confirm the critical role of AbdB-like Hox genes in the development of the autopod, and add to the spectrum of mutations involving triplet repeats.

Fluvoxamine: metabolic fate in animals.

The metabolic fate in animals of the antidepressant compound fluvoxamine was investigated. The 14C-labeled drug was administered orally to dogs, rats, hamsters, and mice, and excretion in urine and feces was measured. Chromatographic patterns of the urines were developed by high performance liquid chromatography. These patterns were used as guides in the isolation of the metabolites, its initial step consisting of concentration of the radioactivity in the urine pools in a conical precolumn, followed by separation in the same HPLC system as used for the metabolite patterns. Altogether, 32 radioactive substances were isolated from the urine pools of the four animal species. They were all identified by the combined use of proton nuclear magnetic resonance and mass spectrometry, and by information obtained from chromatographic behavior and color reactions. Several of the 32 compounds were identical, leaving a total of 11 different metabolites in the four species. In all the animal species, the main focus of fluvoxamine degradation was its aliphatic methoxyl group. In three species, this resulted in the corresponding carboxylic acid as the main metabolite, but in the mouse the corresponding alcohol, in glucuronidated form, was at least as important. In mouse and hamster, the methyl ester was a minor metabolite. Products of acetylation or oxidative removal of the primary amino group accounted for only minor proportions of the metabolite patterns. While fluvoxamine itself has the (E)-configuration, several metabolites occurred both in the (E)- and the (Z)-form. The parent compound was isolated only from the urine of dogs, it accounted for less than 10% of the urinary radioactivity.

Fluvoxamine maleate: metabolism in man.

The metabolic fate of fluvoxamine maleate in man was investigated. The metabolites were isolated from the pooled urines of healthy volunteers who had ingested either 5 mg radioactive, or 100 mg non-radioactive fluvoxamine maleate as a single dose. The main isolation methods were solvent extraction, column and thin-layer chromatography. Eleven metabolites were isolated; eight of these were carboxylic acids. Identification of nine metabolites was accomplished by mass spectrometry supported by information from the UV spectra and the ionogenic properties. The main route of metabolic degradation of fluvoxamine begins with oxidative elimination of the methoxyl group, another route with removal of the primary amino group. In view of the nature of the degradation pattern none of the metabolites is likely to possess psychotropic activity. For the two primary metabolites this has, in effect, been demonstrated.

Dydrogesterone: metabolism in animals.

The metabolic pattern of dydrogesterone was investigated in the rat, dog, mouse, rabbit and rhesus monkey. The drug was administered orally in 3H-labelled form. Following enzymatic hydrolysis of conjugates the radioactive metabolites were extracted from the urine, and in rat and dog also from bile. The separation method used for the development of the metabolite patterns was reversed-phase high performance liquid chromatography. Dydrogesterone and 4 derivatives, known or suspected to be metabolites, were used as marker substances. In all the species a substantial portion of the urinary or biliary radioactivity was too polar to be extracted, or it was not resolved in the chromatographic system used. The radioactivity which did develop into a pattern coincided with two or more of the marker substances. Only in the monkey, the pattern contained a peak of some substance which did not coincide with any marker. The urinary patterns of rat, dog, and mouse differed substantially, from each other as well as from those of rabbit and monkey. The patterns for the latter two animals showed certain similarities, both to each other and to the human urinary pattern as reconstructed from previous studies. It is concluded that with regard to the metabolic fate of dydrogesterone, the rabbit resembles man more than does any other species.

Diflubenzuron: intestinal absorption and metabolism in the rat.

1. The metabolic fate of the insecticide diflubenzuron was investigated in the rat with radioactively labelled forms of the compound. 2. Intestinal absorption, measured as the sum of urinary and biliary excretion, diminished greatly with increasing dose, from about 50% at 4 mg/kg to about 4% at 900 mg/kg. 3. Excretion was almost complete at 72 h after dosing. At that time up to 4% of a dose was recovered from the carcasses of the rats. No detectable excretion of radioactive CO2 occurred (less than 0.5% of dose). 4. The metabolic pattern in urine and bile was investigated with diflubenzuron labelled with both 3H and 14C. No unchanged compound was detected. About 80% of the metabolites appeared to have the basic diflubenzuron structure intact. Three of these, hydroxylated at either aromatic ring, were identified; they were largely excreted as conjugates in the bile. The remainder, also largely excreted in the bile, constituted very polar material. About 20% of the diflubenzuron underwent scission of the ureido bridge. One scission product, 2,6-difluorobenzoic acid, was largely excreted as such in the urine. Its counterpart, 4-chlorophenylurea, was not present in urine or bile in appreciable quantity; nor was 4-chloroaniline detected.