Quadricuspid aortic valves in Syrian hamsters and their formation according to current knowledge on valvulogenesis.

Occurrence of quadricuspid aortic valves has been reported in humans, in nine dogs and in a greater white-toothed shrew. Moreover, two cases of developing aortic valves with four anticipated leaflets have been described in Syrian hamster embryos. Currently, however, no case of quadricuspid aortic valve in adult hamsters has been recorded. The aim here is to present four adults of this rodent species, two of them with unequivocally quadricuspid aortic valves and the other two with quadricuspid-like aortic valves. The four anomalous aortic valves were detected among 4,190 Syrian hamsters examined in our laboratory, representing an incidence of 0.09%. None of the affected hamsters showed apparent signs of disease. The present findings are considered on the light of current empirical knowledge about the morphogenesis of quadricuspid and bicuspid aortic and pulmonary valves. Quadricuspid aortic valves result from the partition of one of the normal mesenchymal cushions which normally give rise to normal (tricuspid) valves, while quadricuspid-like valves might be the product of a combined mechanism of fusion and partition of the cushions at the onset of the valvulogenesis. The presence of aortic valves with four leaflets in ancient mammalian lineages such as insectivors and rodents suggest that quadricuspid aortic valves, although showing almost certainly a low incidence, may be widespread among the different groups of mammals, including domestic animals.

EBP1, a novel host factor involved in primer binding site-dependent restriction of moloney murine leukemia virus in embryonic cells.

Mouse embryonic cells are unable to support the replication of Moloney murine leukemia virus (MLV). The integrated viral DNA is transcriptionally silenced, largely due to binding of host transcriptional repressors to the primer binding site (PBS) of the provirus. We have previously shown that a PBS DNA-binding repressor complex contains ZFP809 and TRIM28. Here, we identified ErbB3-binding protein 1 (EBP1) to be a novel component of the ZFP809-TRIM28 silencing complex and show that EBP1 depletion reduces PBS-mediated retroviral silencing.

Sirenomelia in Bmp7 and Tsg compound mutant mice: requirement for Bmp signaling in the development of ventral posterior mesoderm.

Sirenomelia or mermaid-like phenotype is one of the principal human congenital malformations that can be traced back to the stage of gastrulation. Sirenomelia is characterized by the fusion of the two hindlimbs into a single one. In the mouse, sirens have been observed in crosses between specific strains and as the consequence of mutations that increase retinoic acid levels. We report that the loss of bone morphogenetic protein 7 (Bmp7) in combination with a half dose or complete loss of twisted gastrulation (Tsg) causes sirenomelia in the mouse. Tsg is a Bmp- and chordin-binding protein that has multiple effects on Bmp metabolism in the extracellular space; Bmp7 is one of many Bmps and is shown here to bind to Tsg. In Xenopus, co-injection of Tsg and Bmp7 morpholino oligonucleotides (MO) has a synergistic effect, greatly inhibiting formation of ventral mesoderm and ventral fin tissue. In the mouse, molecular marker studies indicate that the sirenomelia phenotype is associated with a defect in the formation of ventroposterior mesoderm. These experiments demonstrate that dorsoventral patterning of the mouse posterior mesoderm is regulated by Bmp signaling, as is the case in other vertebrates. Sirens result from a fusion of the hindlimb buds caused by a defect in the formation of ventral mesoderm.

Isolation of Bartonella spp. from embryos and neonates of naturally infected rodents.

Embryos and neonatal offspring of wild-captured cotton rats (Sigmodon hispidus) and white-footed mice (Peromyscus leucopus) were tested for the presence of Bartonella spp. Isolates of Bartonella spp. were obtained from 18 of 31 embryos and 7 of 19 neonates from bacteremic dams of the two species; no isolates were obtained from material from non-bacteremic dams. Sequence analysis demonstrated that the isolates from embryos and neonates matched the phylogenetic group of Bartonella spp. isolates obtained from the mother. No antibodies to homologous Bartonella spp. antigens were detected in maternal and neonatal blood or embryonic tissue. These findings suggest the possibility of vertical transmission of Bartonella spp. among natural rodent hosts.

Persistent common atrioventricular canal of the complete form associated with anomalies of the aortic arch system in WKY/NCrj rat fetuses.

Atrioventricular (AV) septal defect with a common AV orifice was found in two near-term rat fetuses, which are descendants of an inbred strain, known to genetically develop tetralogy of Fallot, hypertrophic cardiomyopathy, etc. In one fetus the anterior bridging leaflet was almost entirely committed to the left ventricle but in the other it protruded slightly into the right also, coinciding with type A or type B in humans, respectively. The latter fetus had also a subaortic ventricular septal defect with overriding of the aorta and a double aortic arch. Both fetuses had a narrow pulmonary infundibulum with a muscular band, a dysplastic pulmonary valve, and a markedly hypoplastic ductus arteriosus. Complete AV septal defect and tetralogy of Fallot may be linked genetically, with some common underlying developmental processes.

Tail short variable: characterization of a new mouse mutant, and its possible analogy to certain human vascular disruption defects.

A new mouse mutant, tail short variable (Tsv) produces a reduction deformity of the tail, growth retardation, and, in adults, a mild anemia. Genetic and embryological studies show that on all genetic backgrounds there is variable viability of Tsv/Tsv and Tsv/+ and phenotypic overlap within these and with +/+. A modifier is located to a short segment of chromosome 7, which alters the tail length of Tsv/+ mice up to 15%. The modifier, Tsv, and a coat texture mutant come from the same wild Peru mouse. The tail deformity is associated with, and may be caused by, a vascular disruption of the caudal aorta starting on day 11 of gestation. Thus Tsv appears to be different from each of the thirty known mouse mutants involving the tail. It is suggested that Tsv could be a mouse model for human conditions involving transverse terminal limb defects such as Moebius and de Lange syndromes.

Skeletal morphogenesis: comparative effects of a mutant gene and a teratogen.

As a teratogenic agent retinoic acid (RA) produces severe limb reduction defects if administered at a certain stage of embryonic development. In vitro, RA is able to prevent chondrogenesis and this inhibitory effect is accompanied by the absence of cartilage specific proteoglycans in treated cultures. Such an effect is ruled out as a direct causative factor in teratogenesis for two reasons. First, the limbs of treated embryos show extensive chondrogenesis and this cartilage is normal as far as the expression of biochemical markers of differentiation are concerned. Second, the morphogenetic effects of a mutant gene, cmd, where there is a functional deficit of the proteoglycan core protein are very different from those associated with RA-induced teratogenesis. The differences between the two are not wholly reconciled by the fact that the effects of the mutant gene are cumulative and progressive while those of the RA insult are transitory. There are a number of developmental events which are, however, altered by RA in the mesenchymal cells of the early limb bud such as cell proliferation, cell death, and hyaluronic acid metabolism. Not only any one or more of these factors may secondarily inhibit chondrogenesis but, more importantly, may also have a number of other consequences in the developing embryo. Since a number of cell types besides mesenchymal cells respond to RA by altering their pattern of differentiation, it is conceivable that some fundamental molecular step in the process of differentiation provides a target for its action. In a recent review, Sporn and Roberts (1983) have suggested that to be compatible with the wide ranging effects of retinoids documented so far, any hypothesis put forward for its molecular mechanism of action must include a role in gene expression. No experimental work has yet directly addressed how retinoids might modify gene expression. We believe that along with teratocarcinoma stem cell lines, the use of retinoids as selective teratogens may open up another avenue in search of molecular mechanisms of cell differentiation.

Genetic and developmental studies of a new mouse mutation that produces otocephaly.

A new recessive lethal mutation in mice that produces the otocephaly defect is described. The mutation, provisionally named oto is located on chromosome 1, within, or just outside of, a previously existing inversion, In(1)1Rk, and was probably induced by X-irradiation. The penetrance of oto is nearly complete on C57BL strain backgrounds but is reduced to a variable extent on other backgrounds. The previously reported liability to spontaneous otocephaly in the C57BL strains appears to increase the penetrance of oto. Studies of the sequences of developmental changes (conducted primarily by scanning electron microscopy) and of the range of defects indicate that a primary deficiency involving the anterior aspect of the embryonic disc occurs in affected individuals. An hypothesis related to deficiencies in mesodermal populations is presented as the basis for the craniofacial and brain defects observed.

Extensive multiple innervation and abnormal synaptogenesis in muscular dysgenesis (mdg/mdg) in the mouse embryo.

Muscular dysgenesis (mdg) is an autosomal recessive mutation in the mouse characterized by total muscle inactivity in vivo or in vitro. The muscle fiber in the mdg/mdg diaphragm was not only morphologically abnormal but also multiply innervated; the motor innervation was very dense, showing overgrowth and sprouting. As expected at the ultrastructural level, nerve-muscle contacts were composed of dense appositions of numerous axon terminals (dense focal polyinnervation). Moreover, these mdg/mdg neuromuscular junctions, lacking post-synaptic unfolding, were immature compared to the control ones. This retarded neuromuscular junction differentiation in muscular dysgenesis may be related to considerable delay in muscle maturation and/or abnormal muscular differentiation, or to a nerve defect independent of, or causally related to, the muscular defect.

Double staining technique for rat foetus skeletons in teratological studies.

Cartilage and bone were differentiated using alcian blue and alizarin red S respectively. Anomalies of both cartilaginous and bony parts of the skeleton could be examined.