A compendium of the genetically induced congenital malformations of the house mouse

Transgenerational developmental effects and genomic instability after X-irradiation of preimplantation embryos: studies on two mouse strains

Recent results have shown that irradiation of a single cell, the zygote or 1-cell embryo of various mouse strains, could lead to congenital anomalies in the fetuses. In the Heiligenberger strain, a link between the radiation-induced congenital anomalies and the development of a genomic instability was also suggested. Moreover, further studies showed that in that strain, both congenital anomalies and genomic instability could be transmitted to the next generation. The aim of the experiments described in this paper was to investigate whether such non-targeted transgenerational effects could also be observed in two other radiosensitive mouse strains (CF1 and ICR), using lower radiation doses. Irradiation of the CF1 and ICR female zygotes with 0.2 or 0.4Gy did not result in a decrease of their fertility after birth, when they had reached sexual maturity. Moreover, females of both strains that had been X-irradiated with 0.2Gy exhibited higher rates of pregnancy, less resorptions and more living fetuses. Additionally, the mean weight of living fetuses in these groups had significantly increased. Exencephaly and dwarfism were observed in CF1 fetuses issued from control and X-irradiated females. In the control group of that strain, polydactyly and limb deformity were also found. The yields of abnormal fetuses did not differ significantly between the control and X-irradiated groups. Polydactyly, exencephaly and dwarfism were observed in fetuses issued from ICR control females. In addition to these anomalies, gastroschisis, curly tail and open eye were observed at low frequencies in ICR fetuses issued from X-irradiated females. Again, the frequencies of abnormal fetuses found in the different groups did not differ significantly. In both CF1 and ICR mouse strains, irradiation of female zygotes did not result in the development of a genomic instability in the next generation embryos. Overall, our results suggest that, at the moderate doses used, developmental defects observed after X-irradiation of female zygotes of these two sensitive mouse strains should not be transmitted to the next generation. Paradoxically, other studies would be needed to address the question of a potential increase of fertility after doses lower than 0.2Gy in both strains.

Phenotypic characterization of the transgenic mouse insertional mutation, legless

In this report, we describe the dysmorphologic phenotype associated with the transgenic insertional mutation legless. This autosomal recessive, perinatally lethal mutation results in an interesting pleiotropic array of congenital malformations. The phenotype of the legless mutation in homozygous perinatal mutants is compared to wild-type nontransgenic and heterozygous siblings. Skeletal, craniofacial, and visceral malformations are characterized. We have observed by skeletal analysis a consistent loss of distal hindlimb structures, as well as the loss of distal forelimb structures with a predilection for the preaxial side of the developing forelimb. Craniofacial malformations commonly observed appear to represent a range of severity of affect, with the mildest manifestation evident as apparently shallow lateral clefts of the upper lip and mild midfacial clefts accompanied by clefts of the secondary palate. At the severe end of the spectrum, the midline clefts of the face (and secondary palate) are very wide, with obvious accompanying frontonasal encephaloceles and overt lateral clefts of the upper lip. Examination of the mutant brain has demonstrated marked defects in the anterior structures, particularly the olfactory lobes and cerebrum, in greater than 90% of the brains studied. Observation of the internal viscera has identified transposition of thoracic and abdominal organs in approximately 50% of the mutant offspring. The limb, head, and visceral defects were not observed in the wild-type nontransgenic or heterozygous siblings. Transgenic insertional mutations leading to congenital malformations are useful because the transgene sequence may serve as a tag to facilitate molecular retrieval. Analysis of the flanking DNA sequences will allow the identification of the interrupted gene. A complete description of the mutant phenotype will assist in the understanding of this genetic locus.

Analysis of the syndrome of congenital malformations induced in genetically defined mice by acute riboflavin deficiency

The role of genetics in the expression of a complex syndrome of teratologically induced congenital malformations was examined by the use of three inbred strains and 15 related crosses of mice. The syndrome, which included various limb, brain, orofacial, gastrointestinal, and miscellaneous malformations, was induced by an intense riboflavin deficiency produced by feeding the antagonist galactoflavin during midgestation. Analyses of the data showed that, although all three strains shared the major and most other features of the syndrome, there occurred in its manifestation vast quantitative and qualitative differences among them, in which they were resembled by their related crosses such as to constitute strain-specific malformation patterns. The results can be regarded as typifying an animal counterpart of human situations, the three strains representing in toto the mouse family, each strain individually exhibiting the variety that occurs between siblings in expressing a single syndrome.

Human achondroplasia: defective mitochondrial oxidative energy metabolism may produce the pathophysiology

A summary is presented of previous studies by other investigators of human achondroplasia and dyschondroplastic animal models. In addition, studies previously reported from our laboratories are discussed, and they demonstrate that defective oxidative energy metabolism is present in mitochondrial preparations from achondroplastic human subjects and rabbits (ac/ac) with chondrodystrophy. The results of the studies support the hypothesis discussed fully in the manuscript that a partial defect in mitochondrial oxidative metabolism in achondroplastic subjects is expressed specifically in the growth plates of the long bones because this tissue has the lowest oxygen tension of any bodily organ undergoing active proliferation, thus leading to the achondroplastic phenotype in humans and the ac/ac rabbit. In the ac/ac rabbit phosphorylation at the cytochrome c oxidase region (site III) of the terminal respiratory system was shown to be absent in mitochondrial preparations from the livers of newborn ac/ac rabbits. Normal-appearing littermates did not exhibit the defect. Studies of mitochondrial preparations from human skin fibroblasts (grown in tissue culture) from normal human subjects and subjects with homozygous achondroplasia demonstrated that concentrations of cytochrome a3 were decreased approximately 80% in preparations from homozygous achondroplastic cells. Levels of cytochrome a3 in heterozygous achondroplastic cells were intermediate between the levels in normal cells and homozygous achondroplastic cells demonstrating the effects of gene dosage. Determination of total heme a (as the pyridine hemochromogen) in the normal and achondroplastic preparations from human subjects showed that the observed decrease in concentration of cytochrome a3 in the achondroplastic preparations was due to an absence of cytochrome a3 and not to a change in its absorbancy (extinction coefficient).

Anatomical features associated with preaxial duplication (pd): a recessive mutation in the rat

Preaxial polydactyly of the fore- and hindlimbs was found in Wistar-derived rats in 1978. Genetic analysis indicated that the polydactyly was due to the effects of an autosomal recessive gene (gene symbol; pd). Polydactylous homozygous rats had two or three pollices (six or seven digits) in the forelimbs and one to three preaxial extra digits (six to eight digits) in the hindlimbs. Skeletal examination revealed the presence of the extra carpal, metacarpal, and phalangeal bones that seemed to be complete or incomplete duplication of the navicular, greater multangular, first metacarpal, and phalanges of digit I in the forelimbs. In the hindlimbs, extra tarsal, metatarsal, and phalangeal bones were also observed preaxially. These extra elements seemed to be mirror-image duplications of the talus, navicular, second cuneiform, third cuneiform, cuboid, and metatarsals and phalanges of digits II-V with the absence of the first cuneiform, tibiale, first metatarsal, and phalanges of digit I. In addition, morphological changes were observed in the humerus, radius, and ulna in the forelimbs and femur, tibia, and fibula in the hindlimbs. Especially in the radius and tibia, thickening and bifurcation were found, indicating incomplete duplication of these bones. Based on these findings, the limb anomaly was classified as preaxial carpometacarpal/tarsometatarsal-type polydactyly with incomplete duplication of the radius and tibia. The mutant rats had other associated anomalies such as accessory spleens and cryptorchism. The males are sterile, whereas the females breed normally.

Alterations in cell surface galactosyltransferase activity during limb chondrogenesis in brachypod mutant mouse embryos

The autosomal mutation brachypod (bpH/bpH) in the mouse affects the development of precartilage mesenchymal condensation in the limb-bud. We have previously shown that this defect is localized to the expression of terminal N-acetylglucosamine (GlcNAc) glycoproteins in the plasma membrane (Elmer and Wright, '83). The present study is focused on cell surface galactosyltransferase (GalTase), an ectoenzyme that transfers galactose to its GlcNAc substrate. Purified plasma membrane preparations derived from wild-type (+/+), heterozygote (+/bpH) and brachypod (bpH/bpH) embryonic mouse limb cells were assayed for GalTase activity during in vitro and in utero chondrogenesis using High-Performance Liquid Chromatography (HPLC). On embryonic day E12, prior to overt expression of the mutant gene, no significant difference in GalTase activity was observed. By the third day in culture, all major chondrogenic elements of the autopod were present in +/+ and +/bpH embryos, whereas the mutant autopods were markedly deficient in staining and appeared consistently shorter. The accumulation of alcianophilic cartilage matrix in the wild-type was accompanied by a 29% increase in GalTase activity, which reflected the net change (29%) observed during development from days E12 to E13 in utero. The GalTase activity for the in utero E13 mutant (13%) was significantly different from control. In culture, day E12 mutant autopods actually decreased in their GalTase level by 3 days so that the activity was reduced to only 57% of the wild-type. Though GalTase activity in the heterozygote showed an intermediate expression, optical image analysis did not reveal consistent differences in cartilage development when compared to +/+, arguing against a gene-dosage effect at the gross anatomical level. These data indicate that an increase in plasma membrane GalTase activity is a natural developmental event that occurs during limb-bud chondrogenesis and a decrease in GalTase activity contributes to the dysmorphogenesis in brachypod limb-buds.

Heritable pulmonary lobation anomaly in the rat

A new mutant gene which caused fusion of lung lobes was found in the Wistar rat. The genetic analysis revealed an autosomal recessive inheritance and the mutant gene was named fused pulmonary lobes (gene symbol: fpl). The right lung of the fpl/fpl homozygotes had fused lobes of varying degrees. The fpl/fpl homozygotes were semilethal at the neonatal stage and had externally visible associated malformations such as malocclusion of incisors, eyelid anomalies, and digit abnormalities in the fore- and hindlimbs with different incidences. These traits were considered to be caused by the pleiotropic effects of the fpl gene.

Animal model: skeletal anomalies in mice with cleidocranial dysplasia

Cleidocranial dysplasia in mice, a radiation-induced skeletal mutation, showed striking homology with cleidocranial dysplasia in humans. Genetic studies indicated that the condition in mice is inherited as an autosomal dominant trait with variable expressivity and almost complete penetrance. The homozygous condition was lethal in utero. Radiographic and alcian blue/alizarin red S-stained whole-skeletal preparation studies were used to determine the extent, pattern, incidence, and distribution of skeletal abnormalities in heterozygous mice. Cleidocranial dysplasia in mice was characterized by variable clavicular hypoplasia, delayed closure of cranial fontanelles and sutures, and variable hypoplasia of pelvic bones, in particular ischiopubic rami. The gene symbol Ccd is proposed for the cleidocranial dysplasia mutation in mice and humans.

Developmental genetics

Of particular concern to the human geneticist are the effects of genetic abnormalities on development. To gain an understanding of these effects it is necessary to engage in a reciprocal process of using knowledge of normal developmental events to elucidate the mechanisms operative in abnormal situations and then of using what is learned about these abnormal situations to expand our understanding of the normal. True developmental genes have not been described in man, although it is likely that they exist, but many developmental abnormalities are ascribable to mutations in genes coding for enzymes and structural proteins. Some of these even produce multiple malformation syndromes with dysmorphic features. These situations provide a precedent for asserting that not only monogenic developmental abnormalities, but also abnormalities resulting from chromosome imbalance must ultimately be explicable in molecular terms. However, the major problem confronted by the investigator interested in the pathogenesis of any of the chromosome anomaly syndromes is to understand how the presence of an extra set of normal genes or the loss of one of two sets of genes has an adverse effect on development. Several molecular mechanisms for which limited precedents exist may be considered on theoretical grounds. Because of the difficulties in studying developmental disorders in man, a variety of experimental systems have been employed. Particularly useful has been the mouse, which provides models for both monogenic and aneuploidy produced abnormalities of development. An example of the former is the mutation oligosyndactylism which in the heterozygous state causes oligosyndactyly and in the homozygous state causes early embryonic mitotic arrest. All whole arm trisomies and monosomies of the mouse can be produced experimentally, and of special interest is mouse trisomy 16 which has been developed as an animal model of human trisomy 21 (Down syndrome). In the long run, the most direct approach to elucidating the genetic problems of human development will involve not only the study of man himself but also of the appropriate experimental models in other species.

An inherited limb deformity created by insertional mutagenesis in a transgenic mouse

We have created an insertional mutation that leads to a severe defect in the pattern of limb formation in the developing mouse. The novel recessive mutation is phenotypically identical and non-complementary to two previously encountered limb deformity mutations, and is closely linked to a dominant mutation that gives rise to a related limb dysmorphism. The inserted element thus provides a molecular genetic link with the control of pattern formation in the mammalian embryo.

Morphological and biochemical aspects of monofunctional phosphoramide mustard teratogenicity in rat embryos cultured in vitro

Day 10 rat embryos were exposed in vitro to a monofunctional analog of phosphoramide mustard (MPM) at concentrations of 25 to 200 micrograms/ml (144 to 1,156 X 10(-6) M). After a 24-hour exposure, embryos exhibited a dose-dependent decrease in growth parameters (crown-rump length, number of somites, and protein content) as well as incidence of malformations. Abnormal embryos were characterized by hypoplasia of the prosencephalon as well as hypoplasia of the mandibular arches, tail, and limb buds. Histological analysis revealed abnormal levels of necrotic cells, particularly in the neuroepithelium and surrounding mesenchyme. In all respects embryos exposed to MPM could not be distinguished from embryos exposed to phosphoramide mustard. We also determined using mouse L1210 cells that at the maximum nonlethal concentration used in our embryo exposure experiments, MPM did not cause DNA cross-linking but did cause single-strand DNA breaks. Phosphoramide mustard, at concentrations teratogenic to embryos in vitro, did produce DNA cross-linking. Taken together, our results indicate that although cyclophosphamide (CP)-induced DNA cross-linking may play a role in CP teratogenesis, DNA cross-linking is not an absolute requirement.

A genetic factor controlling morphogenesis of the laryngotracheo-esophageal complex the mouse

A new autosomal, recessive lethal mutation in the mouse cause failure of division of the embryonic foregut into totally separate digestive and respiratory ducts. The newborn homozygote has a cleft that extends between the laryngotracheal and esophageal tubes, allowing excessive air to pass into the stomach and subsequently into the peritoneal cavity. This mutation has been designated lec (laryngotracheo-esophageal cleft). The common region shared by the respiratory and digestive tubes has features characteristic of both structures. Development of cartilage around the laryngotracheo-esophageal complex is also affected in the mutant.