Development of the embryonic trisomy 1 mouse

Integrated disinfection by-products research: assessing reproductive and developmental risks posed by complex disinfection by-product mixtures

This article presents a toxicologically-based risk assessment strategy for identifying the individual components or fractions of a complex mixture that are associated with its toxicity. The strategy relies on conventional component-based mixtures risk approaches such as dose addition, response addition, and analyses of interactions. Developmental toxicity data from two drinking-water concentrates containing disinfection by-products (DBP) mixtures were used to illustrate the strategy. The results of this study showed that future studies of DBP concentrates using the Chernoff-Kavlock bioassay need to consider evaluating DBP that are concentrated more than 130-fold and using a rat strain that is more sensitive to chemically-induced pregnancy loss than Sprague-Dawley rats. The results support the planned experimental design of a multigeneration reproductive and developmental study of DBP concentrates. Finally, this article discusses the need for a systematic evaluation of DBP concentrates obtained from multiple source waters and treatment types. The development of such a database could be useful in evaluating whether a specific DBP concentrate is sufficiently similar to tested combinations of source waters and treatment alternatives so that health risks for the former may be estimated using data on the latter.

Lens and mesenchyme ultrastructure in gestational day 11 trisomy 1 mice

The lenses and head mesenchyme of two 11-gestational day trisomy 1 mouse embryos and a normal littermate were examined using transmission electron microscopy (TEM). One trisomic embryo had a small lens with a lens stalk; the other was aphakic. The resolution available with TEM allowed detailed evaluation of cell organelles, spatial relationships and the intra- and extracellular structural environment of the lens and head mesenchyme in normal and aneuploid embryos. Differences in fine structure between normal and trisomic lenses included (1) type of epithelium, (2) size of intercellular lacunae, and (3) activity of Golgi complexes. Differences in mesenchyme included (1) the number and size of cytoplasmic extensions, (2) shape of the cells, and (3) reduced endotheliomesenchymal interactions.

Ultrastructure of murine trisomy 1 optic cup

The optic cups of two gestational day 11 trisomy (ts) 1 mouse embryos and a normal littermate control were examined using transmission electron microscopy (TEM). One trisomic embryo had a small lens with a lens stalk; the other was aphakic. The resolution available with TEM allowed detailed evaluation of cell organelles, spatial relationships, and the intra- and extracellular structural environment of the optic cup in normal and abnormal mouse embryos. Differences between the normal littermate and the trisomic optic cups, as well as between the two ts 1 structures, included the following: 1) melanin granules in the retinal layer and intraretinal space as well as in the pigment layer, 2) neither pseudostratified nor cuboidal neuroepithelium in trisomic optic cups, 3) increasing cell lysis with severity of eye defect, 4) fusion between retinal and pigment layer cells and cells from the pigment layer and head mesoderm. This investigation not only confirmed some of the abnormal morphology found in light microscopic studies of ts 1 at this gestational age but also identified other anomalies in the ts 1 eye that may play a part in the dysgenesis of this organ. The roles of larger than normal intercellular lacunae, disorganized microtubules, and the connections between different cell types in the ts 1 optic cup require further investigation.

Mitosis in embryonic trisomy 1 mouse eye

Trisomy 1 embryos consistently show eye defects (e.g., aphakia, microphakia, retention of lens stalk). To determine if the plane of division of mitotic figures is abnormal in the eyes of these animals, trisomic embryos (9.5 through 12 gestational days) were produced from mice doubly heterozygous for Robertsonian translocation chromosomes [Rb(1.3)/Rb(1.10)]. To accommodate for the known delay in trisomic embryo development, animals were grouped according to stages of eye development rather than to gestational age. Serial sections were evaluated without knowledge of karyotype for orientation of mitotic figures (parallel, perpendicular, oblique) in lens, optic cup, and diencephalon. Location of mitotic figures was scored as apical (nearest the lumen), middle, and basal. Numerous anomalies were noted in trisomic eye development. No difference was found between orientation of mitotic figures in the lens and optic cup of trisomy 1 and normal embryos. Location of mitotic figures in trisomy 1 lens was significantly different from that of normal littermates. The data confirm earlier studies that trisomy 1 affects the eye, and they tend to corroborate evidence that this trisomy affects the lens more than it affects the optic cup.

Histochemical analysis of extracellular matrix material in embryonic trisomy 1 mouse eye

Trisomic animals produced from mice doubly heterozygous for Robertsonian translocation chromosomes [Rb(1.3)/Rb(1.10)]consistently show eye defects (e.g., aphakia, microphakia, and retention of lens stalk). To determine if changes in distribution or composition of extracellular matrix material may be a factor in development of these defects, eye structures of trisomy (ts) 1 embryos and normal littermates were studied histochemically using the following methods: Alcian blue 8GX, pH 2.5; periodic acid-Schiff (PAS), Alcian blue/PAS combined; high-iron diamine (HID), and HID/Alcian blue combined. Eye development was divided into stages to account for the known delay in ts 1 mouse development. Differences were found in staining patterns as early as stage 1. In later stages, the most consistent difference was an increased period of contact between lens and optic cup due to retardation of interface matrix dissolution between these rudiments in ts 1 embryos. Eyes in which this occurred had abnormally shaped lenses. Overall, the ts 1 optic cup appeared to have fewer staining abnormalities and dysmorphology than did the lens or interface matrix. Triplication of a chromosome may indirectly alter temporal and spatial organization of extracellular matrix through action on cells responsible for the production of this material. Possible mechanisms of action are discussed.