[Corneal anomalies in murine trisomy 16]. / Minoranomalien der Hornhaut bei der murinen Trisomie 16.

BACKGROUND: The prevalence of human Down's syndrome is about 1:700. Investigations using animal models are therefore of clinical relevance for understanding its etiopathogenesis. No corneal changes have been reported with transgenic murine trisomy 16. METHODS: A total of 20 fetal mice (n=40 eyes) with experimentally induced trisomy 16 were investigated from day 18 of pregnancy in order to determine whether visible developmental disorders of the cornea occur. All specimen were investigated microscopically in serial sections. RESULTS: In addition to disturbances in systemic development, the transgenic mouse fetuses showed high rates of malformation of the eyes. Developmental and differentiation disorders of the corneal epithelial cell layers and structural disturbances of the corneal parenchyma were found. Our findings are the first demonstration of developmental disorders of the cornea in mouse fetuses with trisomy 16. These minor anomalies of the cornea could well have resulted in keratoconus if the animals had survived. CONCLUSIONS: Our findings in transgenic mouse fetuses with trisomy 16 correspond to the clinical pattern of Down's syndrome in humans. Disturbed development of lids and lenses have a high prevalence, whereas corneal hypoplasia is found less often.

Mapping of candidate genes for hypertension by fluorescence in situ hybridization on the genome of transgenic rats and mice.

Transgenic animals are new and important models for the study of candidate genes in hypertension research as well as in other fields of medicine. For detailed genetic characterization of the transgenic animals, and to account for the symptoms arising from the insertion of transgenes in the genome, it is essential to identify these insertion sites. In this study, the insertion sites of the transgenes of candidate genes for hypertension were identified by fluorescence in situ hybridization (FISH) after G-banding of the chromosomes in transgenic rats and mice. This technique combines high resolution G-banding and fluorescence in situ hybridization for the mapping of four different candidate genes in six different transgenic rats as well as three different mouse transgenic lines. The presented results will help to draw conclusions about the influence of the respective integration site on transgene expression.

Isolation of glyceraldehyde 3-phosphate dehydrogenase (Gapdh) cDNA from the distal half of mouse chromosome 16: further indication of a link between Alzheimer's disease and glycolysis.

The amyloid precursor protein (APP), which is localized on both human chromosome 21 and its murine counterpart, chromosome 16 and which is involved in the formation of deposits in Alzheimer's disease, could be shown to bind effectively to a glytolytic enzyme: rat glyceraldehyde 3-phosphate dehydrogenase (Gapdh). We report here the isolation of a cDNA of murine Gapdh from mouse chromosome 16 (MMU16) originating from microclones of the distal part of MMU16 and the use of homologous genomic DNA sequences to further screen a cDNA phage library. The cDNA was sequenced, confirmed by polymerase chain reaction following reverse transcriptase (RT-PCR) and the open reading frame was expressed in vitro. The possible localization of Gapdh on MMU16--which may provide a mouse model for Down's syndrome and Alzheimer's disease--may lead to new insights into glycolysis and its role in the two syndromes.

Genesis and systematization of cardiovascular anomalies in murine trisomy 16.

On account of genetic homologies trisomy 16 in the mouse is regarded as an animal model of Down's syndrome. A detailed evaluation of the cardiovascular system in 109 fetuses with trisomy 16 and 422 balanced siblings was performed in order to systematize the cardiovascular anomalies and to elucidate the pathogenetic mechanisms responsible for their formation. 92% of fetuses with experimentally induced trisomy 16 exhibited cardiovascular anomalies. The most common types of anomalies were hypoplasia and aplasia of the aortic arch, which appeared in 85% of the fetuses. Situs inversus of the aortic arch system was remarkably frequent (20%). Hypoplasia or aplasia of the pulmonary artery was seen in 10% of the fetuses. A too proximal insertion of the pulmonary artery into the ascending aorta was observed in 8% of the fetuses.

A multivariate morphometric analysis of hippocampal anatomical variation in C57BL/6 in equilibrium BALB/c chimeric mice.

We investigated hippocampal anatomy in artificially-produced chimeras derived by the aggregation of embryos from two widely-studied inbred mouse strains, C57BL/6J and BALB/cJ. Contrary to expectations, the chimeras were not always intermediate between the parental strains. For a number of characters, the chimeras exceeded qualitatively as well as quantitatively the phenotypical range displayed by both inbred parental strains. These findings imply that if only one parent is available for comparison, for instance, in studies involving a normally inviable genotype, separating effects of this genotype from idiosyncratic effects inherent to the chimeric model will be very difficult, if not impossible.

Defects of skeletal morphology, density, and structure in mouse fetuses with trisomy 16.

Skeletal anomalies present in trisomy 16 in the mouse--an animal model of human trisomy 21--are described. Altogether 27 fetuses with trisomy 16 and 118 chromosomally balanced siblings were examined radiographically and by alizarin staining on day 20 of gestation; the radiographs were analyzed by computer-aided densitometry and structural differentiation. Extensive asymmetry or abnormal fusion of the vertebral centers and alterations of the vertebral arches were observed along with rib malformations (rib-vertebra syndrome). The skull primarily exhibited anomalies of the occipital bone. Ossification of the humerus, femur, and tibia was characterized by reduced mineralization. Typical, fracture-like alterations affecting only the tibia were also observed. Measurement of the lengths of the humeri of fetuses of comparable weight revealed a growth retardation not correlatable with the degree of mineralization. The significance of these skeletal abnormalities with regard to the trisomy 21 syndrome is discussed.

Blastomere karyotyping and transfer of chromosomally selected embryos. Implications for the production of specific animal models and human prenatal diagnosis.

A method is described that permits the generation of four isolated blastomeres after embryo splitting of murine four-cell eggs and the subsequent chromosomal analysis of one of the obtained 1/4-blastomeres. According to the karyograms obtained, embryos can be selected for reimplantation and furthermore triplicated via the embryo splitting procedure. By employing the described experimental setup, it is possible specifically to produce trisomy 16----2n aggregation chimeras as a postnatal model system of human Down's syndrome. The design can also be used for embryo sexing in stock farming and the selective reproduction of sexed farm animals via embryo transfer. Furthermore the application of blastomere karyotyping in human genetic counseling is discussed for the descendants of carriers of Robertsonian translocations. In addition the reported method could be employed for the genotypic identification of early homozygous embryonic stages from persons carrying frequent recessive mutations. The proposed design could, therefore, widen the spectrum of prenatal diagnosis.

Behavioural and developmental abnormalities in mouse trisomy 19: an animal model of mental retardation induced by chromosome imbalance.

Murine trisomy 19 (Ts19) can be regarded as a general model of human trisomies. It is the only autosomal trisomy in the mouse that survives the perinatal period. Therefore, it is the only animal model available for postnatal investigations of trisomy-specific mental retardation. To evaluate the extent of developmental retardation during the late-embryonic and fetal period of gestation, total body weight development was documented for 60 Ts19-fetuses and compared with that of 219 euploid in utero-mates. In addition, a postnatal study on body-weight development of 77 Ts19-neonates and 74 euploid littermates was performed starting on day 1 postpartum and continuing until spontaneous death or until day 22. Forty-seven Ts19-individuals were further tested in nine behavioural test systems in order to determine their neurophysiological developmental profile. Findings were compared with age-dependent morphologic and physiologic parameters. The data obtained in the present study show a significant retardation of organ- and body-weight development in Ts19-mice starting on day 14 of gestation. Retardation of physiological parameters is progressive and persists throughout the perinatal and postnatal periods. Furthermore, the trisomic individuals showed specific behavioural abnormalities.

Genesis and systematization of cardiovascular anomalies and analysis of skeletal malformations in murine trisomy 16 and 19. Two animal models for human trisomies.

On account of genetic homologies, trisomy 16 in the mouse is generally regarded as a direct animal model of Down's syndrome. Mouse trisomy 19, on the other hand, can be seen as a general model of human trisomies. A detailed evaluation of the cardiovascular system and skeleton in 109 fetuses with trisomy 16 and 422 balanced siblings was carried out in order to systematize the cardiovascular anomalies and the pathogenetic mechanisms responsible for their formation according to (1) general retardation, (2) genetically determined impairment of neural-crest cell migration, and (3) direct gene action on organogenesis. Skeletal malformations in the form of a rib-vertebra syndrome encountered in Ts 16 are described here for the first time. In 108 fetuses and 219 neonates resulting from cross-breeding to induce trisomy 19, we found no significant increase in the frequency of the foregoing anomalies. These results are discussed with regard to a chromosome-specific genetic influence as opposed to a general effect of chromosome imbalance. The specificity of the Ts16 syndrome is compared with that of individual organ anomalies as can be induced by teratogenic agents. Our investigation shows that specific malformation patterns of a particular type can be produced by a variety of methods. However, the overall patterns of the two syndromes are highly chromosome-specific. On detailed examination, the malformation pattern of mouse trisomy 16 shows significant similarities with that of human trisomy 21.

2-Amino-4-phosphonobutyric acid selectively blocks two-way avoidance learning in the mouse.

There seems to be ample evidence supporting the view that glutamate plays a significant role in the mammalian brain as a neurotransmitter. It is considered to be a likely transmitter candidate in one or more hippocampal pathways. Recently it has been visualized in excitatory, possibly glutamatergic, neurons in the hippocampus. Glutamate has been proposed to mediate memory formation. We wanted to see if blocking glutamate action by a specific glutamate antagonist could result in reduction of learning ability. 2-Amino-4-phosphonobutyric acid (APB) is an analogue of glutamic acid and has been used as a glutamate antagonist in electrophysiological studies on invertebrate neuromuscular junction, retina and hippocampus. We tested the influence of APB on the acquisition of two way avoidance learning in the shuttle box and on learning in the water maze. Our results show that intraperitoneal injection of APB led to a reduction in avoidance learning, whereas learning in the water maze was unaffected.

Elimination of X-ray-induced chromosomal aberrations in the progeny of female mice.

Female NMRI mice were irradiated with various doses of X-rays and induced chromosome aberrations were scored in MII oocytes (Dosage: 0.222, 0.666, 2 and 6 Gy). After irradiation with 2 Gy, early zygotes were examined in the 2-cell stage; additional dominant lethals were counted and surviving embryos were examined after 13.5 days of pregnancy. 87.2% of the MII oocytes showed structural chromosomal aberrations after irradiation with 2 Gy. Surviving embryos, however, failed to show any increase in the aberration rate. This result points to (almost) complete elimination of genetically damaged oocytes and zygotes already before birth. In addition to the structural aberrations, aneuploidies were induced. Most of them, however, were hypoploidies. Hence, the study confirmed the well-known susceptibility of oocytes around the time of fertilization for induced chromosome loss. Induced hyperploidies, however, were very rare. Evidence for induction of meiotic non-disjunction was weak. In surviving embryos, no increase in numerical aberrations, either hypoploid or hyperploid was discovered. The significance of these data for the prediction of chromosomal damage due to to ionizing radiation in humans is discussed. Recent risk estimates of UNSCEAR and other agencies represent very cautious upper levels.

Mammals as model organisms for the study of the biologic basis of human behavior.

Behavioral phenotypes that are studied in mammals are seldom specific for the understanding of the biologic basis of human behavior. Phenomenologic comparisons primarily demonstrate the existence of genetically determined variabilities and do not allow for any further interpretations. A satisfactory state--using systems of lower complexity--will be reached when neuromorphologic or neurochemical variations can be traced back to phenomenologic differences with single-gene modes of inheritance. In a new study extensive data prove the single-gene inheritance of active avoidance learning. A correlated study carried out in a behavioral genetics and neuroanatomical laboratory showed that, owing to strain differences in mice, there is some probability of a multiple allelic system correlating with the hippocampal mossy fiber distribution.

Individual hippocampal mossy fiber distribution in mice correlates with two-way avoidance performance.

Mice systematically bred for randomization of their genotype show large individual differences when performing a two-way avoidance task (shuttle-box learning). Their behavioral scores correlate strongly (r = -0.80, P less than .01) with the number of mossy fibers synapsing on basal dendrites of hippocampal pyramidal neurons, poor avoiders having relatively more such terminals. This confirms previous findings showing that rat and mouse strains known for genetically dependent poor avoidance learning have extended intra- and infrapyramidal mossy fiber projections.

Monogene inheritance of learning speed in DBA and C3H mice. A behavioral genetic study in the shuttle-box.

We carried out investigations on C3H, NMRI, C57Bl/6, Balb/c, Balb/cN, and DBA inbred mouse strains in the shuttle-box to see whether their learning behavior is genetically controlled. The highly different learning behavior of the parental strains made it possible to test the F1 hybrids and the F2 generation. The environmental influences were standardized as much as possible. In particular, influences possible during the lactation period were excluded by using foster breeding. The results enable us to postulate monogenic inheritance for the learning speed in the shuttle-box. The inheritance is interpreted as codominant. The investigations are part of a basic study in mammalian behavior genetics from the human genetic aspect.