During early embryogenesis, the transcription factor HNF3beta is expressed in visceral and definitive endoderm, node, notochord and floorplate. A targeted mutation in the HNF3&bgr ; gene results in the lack of a definitive node and notochord. Furthermore, lack of HNF3beta results in failure of proper primitive streak elongation. To address whether HNF3beta is required in visceral endoderm, we h...

Vertebrate somitogenesis is associated with a molecular oscillator, the segmentation clock, which is defined by the periodic expression of genes related to the Notch pathway such as hairy1 and hairy2 or lunatic fringe (referred to as the cyclic genes) in the presomitic mesoderm (PSM). Whereas earlier studies describing the periodic expression of these genes have essentially focussed on later st...

The regionalisation of cell fate in the embryonic ectoderm was studied by analyzing the distribution of graft-derived cells in the chimaeric embryo following grafting of wheat germ agglutinin--gold-labelled cells and culturing primitive-streak-stage mouse embryos. Embryonic ectoderm in the anterior region of the egg cylinder contributes to the neuroectoderm of the prosencephalon and mesencephal...

Mouse embryos homozygous for the mutation embryonic ectoderm development (eed) exhibit a growth defect and fail to gastrulate normally. While extraembryonic mesoderm is produced extensively, very little embryonic mesoderm is detected in eed mutant embryos, and there is no subsequent organization of mesoderm into node, notochord, or somites. The phenotype is consistent with a defect in the dista...

6 LLE Review, Volume 73 A streak camera is an electro-optic instrument capable of resolving high-speed, low-repetition-rate, pulsed laser phenomena. The basis of the instrument is a streak tube. The image of the light to be analyzed is focused onto a photocathode at the input end of the streak tube. The photocathode emits electrons in response to the intensity of the light. The electrons, focus...

A microsurgical grafting technique has been used to introduce primordial germ cell (PGC) precursors into intact primitive-streak-stage mouse embryos in vitro. Operated embryos were cultured for 36-40 h and then analysed by a combined histochemical and autoradiographic method. PGC chimaerism occurred in embryos that received grafts of caudal primitive streak cells but not adjacent embryonic endo...

PURPOSE To compare measurements of eccentric fixation using two different targets for fixation, a traditional visuoscope target and the streak target of an ophthalmoscope. PATIENTS AND METHODS Monocular fixation was evaluated using visuoscopy in 47 patients ranging in age from 4 months to 22 years. Visuoscopy measurements were compared using both the traditional visuoscope target and the stre...

A maximum a posteriori algorithm for reduction of metal streak artifacts in x-ray computed tomography is presented. The algorithm uses a Markov random field smoothness prior and applies increased sampling in the reconstructed image. Good results are obtained for simulations and phantom measurements: streak artifacts are reduced while small, line-shaped details are preserved.