Cleft lip with or without associated cleft palate [CL(P)], one of the most common human malformations, is believed to be caused by a combination of genetic and environmental factors. To study the morphological manifestations of genetic factors in this interaction, we compared the embryonic development of the CL/Fr mouse strain (with a mean incidence of 36% spontaneous CL(P) in our colony) with that of the C57B1/6J mouse strain (with no CL(P) in our colony). Results from our scanning electron microscopic study demonstrated that, when compared with C57B1/6J embryos, CL/Fr embryos have several developmental differences including: 1) altered facial geometry, 2) depressed ability of the surface epithelium of primary-palate primordia to participate in the fusion process, and 3) variable hypoplasia of the lateral nasal prominences. We suggest that all of these alterations may contribute to the pathogenesis of CL(P) in the CL/Fr mouse strain.

This paper describes alterations in the incidence of cleft lip and palate in CL/Fr mice subsequent to experimental manipulation of maternal respiratory oxygen levels during a critical period of pregnancy. Only a few previous studies have shown that the incidence of some "genetically determined" malformations in mammals can be decreased by environmental procedures. In addition to demonstrating a decreased incidence ofcleft lip and palate subsequent to maternal hyperoxia on gestational days 10 and II in a genetically susceptible strain, the results ofthe present study show that hypoxia at this time increases the incidence ofcleft lip and palate.The mother, placenta, and embryo form a functional system. This biological association makes all three components vulnerable to physiological and pathological changes in any part ofthe system. The significance of this interdependence is demonstrated by the experimental reduction ofthe incidence ofdefects with genetic predisposition by manipulation of the maternal environment. Erway et al. (1,2) demonstrated that abnormal otolith development in the pallid mouse (a homozygote for a mutant gene) can be prevented by giving pregnant females a diet containing high levels ofmanganese. Supplementation with this element was also effective in reducing otolith malformations and agenesis in the analogous pastel mink (3). Hereditary brachydactyly in rabbits, an autosomal recessive trait, is associated with hemorrhagic necrosis that destroys the tissues in limbs of fetuses. Petter et at were able to prevent this malformation by subjecting pregnant rabbits of this strain to hyperoxia (4) or by supplementing their diet with folic acid plus vitamin B-12 or with folinic acid (5). Millicovsky and Johnston (6) recently reported that maternal hyperoxia greatly decreases the incidence ofphenytoin (Dilantin)-induced cleft lip and palate in A/J mice.The CL/Fr mouse has an incidence of spontaneous cleft lip (which is almost invariably associated with cleft palate) of 35-40% in near-term fetuses in our colony. Our observations ofgravid uteri and concepti ofCL/Fr mice often revealed uterine and placental cyanosis and facial hematomas in the fetuses. Based on the hypothesis that these vascular disturbances may result from deficient circulatory function in the maternal-placental-embryonic complex, we designed the present study to evaluate the potentials of hyperoxia and hypoxia to alter the incidence of cleft lip and palate in this strain. We studied the effects ofhypoxia because an increase in facial malformations in response to this treatment would provide further evidence that maternal factors may mediate birth defects. To our knowledge, a decrease and an increase in the incidence of a genetic malformation in response to variation in the maternal environment has not been demonstrated heretofore. MATERIALS AND METHODSFifteen pregnant animals were divided into three groups offive each and housed in environmental chambers which contained food, water, and bedding material and permitted control ...

The A/J mouse has been used to study the teratogenic affects of phenytoin. The developmental abnormalities produced in offspring of this model are similar to some of the malformations observed in cases of human "fetal hydantoin syndrome." Placing pregnant A/J mice in a hyperoxic chamber after phenytoin injection greatly reduces the incidence of phenytoin-induced cleft lip and palate. These results suggest that phenytoin may affect embryonic development indirectly by altering maternal physiology. This maternally mediated mechanism, and the protection against it afforded by hyperoxia, has general implications for the effects of maternal toxicity on teratogenesis.

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The early cardiovascular (CV) responses of New Zealand white rabbit embryos in situ subsequent to maternal SC injection with hydroxyurea (HU) were analyzed by in vivo microscopic methods. Laparotomies were performed on gestational day 12, and the gravid uteri were exteriorized. The embryos were exposed by careful incisions of the uterine wall and reflection of the extraembryonic membranes. Temperature, water, and electrolyte homeostasis were maintained throughout all procedures. Maternal injection with HU at a teratogenic level (750 mg HU/kg) caused alterations in the embryonic CV system as early as 2 minutes post-treatment. Typically, within 4 minutes the embryonic craniofacial region responded with dilations of the anterior cardinal vein (ACV) and its tributaries. The ensuing pathological events included petechial hemorrhages and hematomas in the forebrain, postocular region, mandibular and nasal processes, and apparent collapse of the vasculature in the forelimb bud. Many embryos exhibited pericardial hemorrhage within 9 minutes. The most severely affected embryos displayed cardiac tamponade and stasis of blood flow through the cardiac chambers. In contrast, control embryos, which received either no drug treatment of SC injection of saline at various osmolarities and pH's, demonstrated none of the CV changes reported above, even after 120 minutes. Low doses of HU (500 mg/kg) produced only ACV dilations in some embryos by 30 minutes. Histologic analysis of HU embryos confirmed the in vivo microscopic observations. The drastic CV derangements exhibited by many embryos may be one of the causes for the high resorption rates associated with the treatment. Furthermore, since teratogenic doses of HU produce immediate hemorrhages and hematomas in the embryos in the same craniofacial areas which are later deformed in the term fetus, it is possible that the teratogenic action of this drug may be related to the initial vascular embryopathies.