The Dumbo rat mutant: a cytogenetic, morphologic and sagittal morphometric analysis.

OBJECTIVE: To study the possibility of use Dumbo rat as, experimental model for understanding abnormal craniofacial development. DESIGN: We investigated craniofacial morphogenesis in the Dumbo rat by morphologic and morphometric technics. We also performed a cytogenetic study of this rat. Wistar strain was considered as control. For morphologic and morphometric studies, we used Dumbo and Wistar embryos at E15 to 21. We stained these embryos in toto with alcian blue and alizarin red. The skeletons of the embryos were examined and drawn under a Lucida camera, and the following sagittal measurements were taken: zygomatic length and thickness, length of the mandible and its anterior and posterior thicknesses, length of the maxillary, and petrous bone height. Statistical analyses were realized using Mann Whitney test in SPSS. For cytogenetic study, chromosome spreads were prepared from lymphocyte cultures obtained from the blood of adult rats of both strains. RESULTS: The Dumbo embryos exhibited hypoplasia of the zygomatic, maxillar and mandibular bones, and micrognathia, evoking some human dysmorphogenesis . Moreover, the position of the preliminary ear was abnormally low. The differences in the measurements of the craniofacial structures between the two groups of rats are significant. However, the cytogenetic study did not reveal any differences between the two strains. CONCLUSION: Our data indicate that the considerable morphometric differences between the craniofacial structures of Dumbo and Wistar rats might be due to genetic mutations that are undetectable by chromosome mapping. Further histologic and genetic analyses might contribute to elucidate the early determinism of the Dumbo phenotype.

The influence of the genetic background on the interaction of retinoic acid with Lx mutation of the rat.

The teratogenic effect of RA was found to be significantly influenced both by genetic background and by the genotype of malformation mutation Lx. The presence of the Lx mutation and BN genetic background strongly increases the teratogenic effect of RA. On the contrary, the SHR genetic background was shown to protect foetuses from RA teratogenic affliction. Recombinant inbred strain BXH2 is endowed with a specific combination of BN and SHR genes, and following RA administration it exhibits the same embryolethal effect as the BN genetic background alone. Without the Lx mutation there was no effect of RA on hind limbs in SHR/SHR or SHR/BN progeny whilst there was a significantly higher occurence of oligodactyly in SHR/BN on forelimbs as compared to SHR/SHR (92.2% vs 11.5%). In +/Lx progeny, forelimbs were significantly more afflicted with oligodactyly in SHR/BN +/Lx in comparison with both SHR/SHR and SHR/BXH2 foetuses, which indicates that BN modifiers responsible for oligodactyly were not passed to the BXH2 strain. On the contrary, hind limbs of SHR/BXH2, +/Lx progeny exhibited the highest affliction (62% of polydactyly and/or oligodactyly). In homozygous Lx/Lx progeny, polydactyly prevailed in forelimbs of SHR/BXH2 following RA administration, whilst in BN/BN progeny oligodactyly was the most frequent affliction. On the hind limbs, the highest reduction of toe number after RA treatment was connected with BN modifiers. The polymorphism of normal morphogenetic factors was shown to be responsible not only for Lx. phenotypic manifestation, but also for the variability in the response to RA teratogenic action.

The role of cell death in limb development of rats manifesting Lx allele on different genetic backgrounds.

Control of vertebrate digital pattern is a phylogenetically old mechanism. Animal strains with abnormal digital counts are a useful model system to study tissue, cell and molecular factors involved in limb patterning. The aim of this study was to investigate rat limb morphogenesis on gestation days 13 to 16 in normodactylous, polydactylous and oligodactylous fetuses where the deviation from the normal pentadactylous phenotype is caused by interaction of mutant Lx allele with different genetic backgrounds. General development was assessed by measurements of crown-rump length, and limb morphogenesis by hand and foot plate width. Skeletogenesis was studied histologically and by whole mount staining with Alcian Blue and Acridine Orange. Cell death was demonstrated by supravital staining and fluorescence microscopy and by standard histology on serial sections. No phenotypic differences among the groups were noted on day 13. On day 14, the oligodactylous hind limb buds were more spiky than normal and had well-developed preaxial necrotic site (foyer preaxial primaire) which was normally observed only on day 15. This area of programmed cell death was severely attenuated in polydactylous limb buds. Pollex triphalangy manifested as increased hand plate width from day 15. Also hind limb buds width differed by this stage between groups. No acceleration or retardation of skeletogenesis was observed in abnormal limbs. The data confirm the crucial role of spatial and temporal patterns of morphogenetic programmed cell death in control of digital pattern.

Anomalies of fetal development in GK rats.

Fetal development was investigated in Goto-Kakizaki (GK) rats. Between days 15 and 20 after identification of a positive sperm plug, the GK rats gained less weight than control animals. The number of conceptuses in each litter was not significantly different in control and GK rats. The incidence of abortive fetal development, however, averaged 39.7% +/- 9.1% in GK rats, compared with only 5.6% +/- 0.2% in control animals. The placental weight in living fetuses was slightly lower in GK rats than control rats. The crown-rump length was identical in the fetuses of control and diabetic mothers. The number of ossification points in the lumbosacral spine, pelvic girdle and anterior and posterior limbs was significantly lower in fetuses of GK rats than control animals. These anomalies could not be blamed on a lower plasma insulin concentration in GK than control animals, whether before or during (days 15-20) pregnancy. Moreover, in both control and GK rats, the insulinogenic index was raised during pregnancy. These findings indicate that GK rats represent a new model for the study of diabetes-related fetal anomalies, their pathogenesis and prevention.

Prenatal development of the Brattleboro rat is influenced by genotype and lysine vasopressin treatment of the mother.

Homozygous (Hom) Brattleboro rats suffer from severe diabetes insipidus (DI) as a consequence of the lack of arginine-vasopressin (AVP) in the brain. Compared with heterozygous (Het) AVP-synthesizing Brattleboro rats, Hom rats show disturbed body and brain development. In this study breeding experiments with Het and Hom rats were performed to determine whether prenatal conditions might contribute to the developmental disturbances in Hom pups. For this purpose Het and Hom females were mated with Hom and Het males, respectively. In addition lysine-vasopressin (LVP) was administered to half of the pregnant females, since this has previously been shown to stimulate birth weight of Hom pups. On day 1 postnatally the body and brain weight of Hom pups of nontreated Hom mothers was significantly smaller than that of the Het litter mates, whereas no difference was found between the weight of Het or Hom pups of nontreated or LVP-treated Het mothers. These results indicate an important role of the genotype of the mother in prenatal development of Hom pups. LVP administration failed to diminish the growth deficits, but increased protein and DNA content of the cerebellum of both Het and Hom pups. Notwithstanding the improved prenatal growth of Hom pups from Het mothers, postnatally retarded development was still observed: at 1 month of age there was a significant difference between the body, brain and cerebellar weight of Het and Hom pups from Het mothers. It was therefore concluded that the prenatal situation of the Hom mother, i.e. AVP-deficiency, significantly contributes to the developmental disturbance of the Hom pup, but also that growth impairment is linked to the presence of the mutation in the Hom pups themselves.

Facial and neuroepithelial abnormalities in a neurological mutant with congenital hydrocephalus. A scanning electron microscope study.

This investigation was carried out to determine the early structural abnormalities of the cephalic region in a genetic mutant of the rat characterized by prenatal aqueductal stenosis and hydrocephalus. The appearance of hydrocephalic and control embryos was examined on days 13-15 of gestation, and the structure and organization of the neuroepithelium and basal lamina were studied using scanning electron microscopy. In addition to some overall developmental delay, hydrocephalic embryos were characterized by abnormalities of forebrain and midbrain development, and eye and external ear anomalies. There were also associated defects of the midfacial region. The lateral cell surface of the neuroepithelium reflected the developmental delay of hydrocephalic embryos, and failed to undergo the morphogenetic cell-shaping changes seen in control embryos. There were also variations in the number of lateral cell-cell specializations as well as regions of neuroepithelial disorganization and occasional herniation into the mesenchymal compartment. The role of the neuroepithelial basal lamina and extracellular matrix in the development of these defects is considered.