The laboratory is engaged in problems of experimental and clinical teratology with the aim of contributing to knowledge on the etiopathogenesis of developmental defects. Only a small part of inborn defects in man is explained either by prenatal exposure to a harmful external factor (15% of cases) or by genetic reasons (20% of cases). Most developmental defects (65%) are thought to result from prenatal exposure to the combined effect of several sub-threshold doses of external factors that act either simultaneously or sequentially; a genetic predisposition is presumed in some of these cases. Our research is focused on the identification of mechanisms implicated in the origin of developmental disturbances induced by either external or genetic factors in two models - chick embryogenesis and mouse odontogenesis, respectively.
      Research at the Department of Teratology focuses on the following main topics:
- Chick embryogenesis
- Mouse odontogenesis
- Craniofacial malformations in man

      In recent years, the chick embryo model has been defined as a tool of experimental teratology, and a method of experimental intervention by external factors has been worked out and standardized in our Department.
      Cleft beak in chicks is employed as a model to verify the hypothesis that a subthreshold dose of an external harmful factor can also induce a developmental disturbance, provided it acts repeatedly or in combination with other factors.
      Our original test method for embryotoxicity in the chick embryo allowed us to estimate minimum embryotoxic doses for chemical substances (drugs, harmful chemical and physical factors). Using this method, we have also predicted the range of embryotoxic doses of vitamin A. Vitamin A was later determined to be the most treacherous human teratogen.
      The rRNA transcription intensity appeared to be a sensitive marker of latent developmental alterations without structural defects. In chicks, embryonic proerythroblast and hepatocyte rRNA transcription was significantly decreased following a single administration of embryotoxic factors. We focused also on the target organ toxicity of chemical compounds within the peripheral nervous system, especially on the study of pathogenic mechanisms involved in the development of peripheral sensory neuropathy. Organotypic cultures of dorsal root ganglia maintained with a semi-solid culture medium represent the main model system used in these studies. These approaches also allow us to reveal factors that do not lead to a gross structural malformation at the organism or organ levels, but that may induce minor structural defects at the tissue level, potentially resulting in postnatal functional deficiency of the corresponding organ.

Fig. 1: The mean incidence of orofacial clefts in the districts of the Czech Republic during 1983-1997.

      Our data may contribute to an elucidation of the etiopathogenesis of most inborn defects in man, where neither exposure to a strong external factor nor any genetic disturbance can be found.

      A functionally specialized dentition is present in mice: each jaw quadrant includes one permanently growing incisor separated from three molars by a toothless jaw segment - the diastema. We have investigated the prenatal development of mouse dentition using qualitative and quantitative histology, 3-D computer-assisted reconstruction and an in situ hybridization method. The mouse functional dentition appears to originate by secondary reduction of the embryonic, more numerous, dental pattern. Either their integration during incisor development or their regression in the prospective diastema results in the reduction of the tooth primordia. Also, the large tooth primordium, which has been generally considered as the early stage of the first molar, appears to be just a rudimental structure in front of the real molar tooth. Epithelial apoptosis is involved in the regression of the rudimental tooth primordia and the positioning of the mesial end of the first molar tooth in mice. The apoptosis has been classified as programmed cell death: BMP-4 and BMP-2 appeared to be involved in its regulation. From this aspect, mouse odontogenesis represents a natural tool for studies of the mechanisms regulating the existence of tooth-bearing and toothless areas in dentition.
      The normogenesis data are compared with the tabby (EDA) mice in which disturbances of tooth development occur due to an altered genotype. The aim isto identify some morphogenetic mechanisms and regulatory factors involved in the determination of tooth number, shape and size. The results may contribute to elucidating the etiopathogenesis of some dental defects in man. (This part of our research is conducted in collaboration with the INSERM U-595, Strasbourg, France).

      Our experimental observations in the mouse revealed the participation of a developmental disturbance of the mandible during the origin of an isolated cleft palate. In patients with isolated cleft palate, a shortening of the mandible has also been recorded, associated with a higher frequency of hypodontia in the lower jaw. The correspondence between experimental and clinical findings suggests that the mechanisms involved in the origin of a cleft palate in experimental animals operate also in man.
      In patients with orofacial developmental disturbances, roentgenometric and anthropometric methods are used to assess the effectiveness of surgical and orthodontic procedures and to evaluate the adequacy of their final outcome. Attention is paid to facial growth patterns and their effect on the therapeutic results. Postnatal lesions resulting from prenatal impairment of morphogenetic functions are analysed in detail, contributing to the elucidation of the etiopathogenesis of these malformations. Current research projects are focused on predicting the postnatal growth of the jaws and on detecting factors that promote the severe skeletal and dental anomalies associated with orofacial clefts.

Fig. 2:
A. Patient with unilateral cleft lip.
B. Injection of a test substance into the amniotic sac of the chick embryo in ovo.
C. Unilateral cleft beak in the chick embryo after intraamniotic injection of styrene on day 4.
D – F. The first upper molar in the mouse. Computer aided 3D reconstruction of the dental epithelium (D) and papilla mesenchyme (E) at embryonic day 19.0. F – functional tooth in the adult mouse.