Gene targeting was used to create a null allele at the epidermal growth factor receptor locus (Egfr). The phenotype was dependent on genetic background. EGFR deficiency on a CF-1 background resulted in peri-implantation death due to degeneration of the inner cell mass. On a 129/Sv background, homozygous mutants died at mid-gestation due to placental defects; on a CD-1 background, the mutants lived for up to 3 weeks and showed abnormalities in skin, kidney, brain, liver, and gastrointestinal tract. The multiple abnormalities associated with EGFR deficiency indicate that the receptor is involved in a wide range of cellular activities.

Lumican, a prototypic leucine-rich proteoglycan with keratan sulfate side chains, is a major component of the cornea, dermal, and muscle connective tissues. Mice homozygous for a null mutation in lumican display skin laxity and fragility resembling certain types of Ehlers-Danlos syndrome. In addition, the mutant mice develop bilateral corneal opacification. The underlying connective tissue defect in the homozygous mutants is deregulated growth of collagen fibrils with a significant proportion of abnormally thick collagen fibrils in the skin and cornea as indicated by transmission electron microscopy. A highly organized and regularly spaced collagen fibril matrix typical of the normal cornea is also missing in these mutant mice. This study establishes a crucial role for lumican in the regulation of collagen assembly into fibrils in various connective tissues. Most importantly, these results provide a definitive link between a necessity for lumican in the development of a highly organized collagenous matrix and corneal transparency.

Mouse embryos homozygous for the allele eed(l7Rn5-3354SB) of the Polycomb Group gene embryonic ectoderm development (eed) display a gastrulation defect in which epiblast cells move through the streak and form extraembryonic mesoderm derivatives at the expense of development of the embryo proper. Here we demonstrate that homozygous mutant ES cells have the capacity to differentiate embryonic cell types both in vitro as embryoid bodies and in vivo as chimeric embryos. In chimeric embryos, eed mutant cells can respond to wild-type signals and participate in normal gastrulation movements. These results indicate a non-cell-autonomous function for eed. Evidence of mutant cell exclusion from the forebrain and segregation within somites, however, suggests that eed has cell-autonomous roles in aspects of organogenesis. A requirement for eed in the epiblast during embryonic development is supported by the fact that high-contribution chimeras could not be rescued by a wild-type extraembryonic environment.

Deletion complexes consisting of multiple chromosomal deletions induced at single loci can provide a means for functional analysis of regions spanning several centimorgans in model genetic systems. A strategy to identify and map deletions at any cloned locus in the mouse is described here.

Abstract-The death of a control subject after an oral load of methionine for a study of the possible relationship between homocysteine and Alzheimer's disease is reported. The subject developed postload plasma concentrations of methionine far beyond those reported previously in humans given the usual oral loading dose of methionine (100 mg/kg body wt). Her preload plasma metabolite values rule out known genetic diseases that might predispose one to unusually high methionine concentrations. The most likely explanation for these events is that the subject received a substantial overdose of methionine. The possibility that extremely high methionine concentrations may lead to severe cerebral effects is discussed, and it is recommended that any move to increase the sensitivity of the usual methionine loading test by increasing the dose of methionine either not be undertaken or be taken only with extreme care. Key Words: methionine load elevation Ⅲ cerebral death T he present article reports the death of a control subject after an oral methionine load for a study of the possible relationship between elevation of plasma total homocysteine (tHcy) 1 and Alzheimer's disease. Elevation of plasma or serum tHcy (hyperhomocysteinemia) is widely recognized to be an independent risk factor for vascular disease. 2 Such elevations have also been associated with Alzheimer's disease. [3][4][5] Although this finding is consistent with the hypothesis that vascular disease may be a contributing factor in the pathogenesis of Alzheimer's disease, 3,6 it is presently uncertain whether the elevated tHcy is a cause or a consequence of the disease. 5 Administration of an oral load of methionine, the ultimate metabolic precursor of homocysteine, at a dose of 100 mg/kg body wt is a widely used means to test for a tendency to manifest hyperhomocysteinemia. 7,8 The available evidence, based on the results of at least many hundreds of such tests, indicates they are generally very safe (see Discussion for further details). In the present case study, we report a death after what seems very likely to have been an overdose of methionine. MethodstHcy, methylmalonic acid, sarcosine (N-methylglycine), cystathionine, total cysteine, and N,N-dimethylglycine were assayed as previously described by using gas chromatography/mass spectrometry. 9 -12 Because the undeproteinized samples were initially treated with a reducing reagent that cleaves all disulfide bonds, tHcy and total cysteine were measured in this assay. Methionine was assayed by column chromatography. S-Adenosylmethionine (AdoMet) and S-adenosylhomocysteine (AdoHcy) were assayed as described. 13 Methionine transamination (TAM) metabolites, the sum of methanethiol released sequentially into the gas phase at pH 7 (protein-S-S-CH 3 ), pH 10 (X-S-S-CH 3 ), and pH 12.5 to 13 (chiefly 4-methylthio-2-oxobutyrate), 14 were determined as described. 15 Phosphatidylcholine and free choline were assayed as described. 16 Betaine was assayed by an unpublished method with the use of liquid chromatography/elec...