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Models in developmental biology continue to yield valuable insights, yet do not play a strong role as guides to experiment. This may be because of the largely unexplored complexity of most developing organisms, and the fact that the most powerful models work at a very abstract level. In Dictyostelium discoideum, however, a fully formed model incorporating detailed experimental results is now available.
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This study presents a computational approach for the deformation analyses of problems in cell and developmental biology. Cells and embryos are viewed mechanically as axisymmetric shell-like bodies containing a body of incompressible material. The analysis approach is based on the finite element method. It is comprised of three finite element ingredients: an axisymmetric shell/membrane element valid for modeling finite bending, shearing and stretching; a volume constraint algorithm for modeling the membrane-bound incompressible material; and a contact algorithm for modeling the mechanical interactions between deformable bodies. Part II of this study will demonstrate how these three ingredients can be applied to analyze mechanical experiments on cells. This same method is also useful for simulating embryonic shape changes during development.
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A review is given of the advances in our knowledge of the developmental biology of the so-called cyst-forming coccidia in the years from 1974 to 1978. Until 1970 only 6 Isospora species were known to occur in cats, dogs and men. After the discovery of the coccidian nature of the genera Toxoplasma, Sarcocystis, Besnoitia and Frenkelia, and after the discovery of the new genus Hammondia the number of known species rose to over 30. In addition it could be shown that also birds of prey, owls and reptiles serve as final hosts for several Sarcocystis and Frenkelia species. The coccidia with isosporoid oocysts can be classified into two major groups: Species with gamogony and sporogony in the final host (Sarcocystis, Frenkelia) and species with schizogony and gamogony in the final host and sporogony on the ground (Isospora, Cystoisospora, Hammondia, Toxoplasma, Besnoitia). The subdivision of the first group into the genera Sarcocystis and Frenkelia based on the localization of their cysts in the musculature and in the brain, respectively, cannot be upheld in the future. Their classification into organisms with small cystozoites of about 7 microm with birds or reptiles as final hosts (Sarcocystis and Frenkelia species of rodents) and those with large cystozoites of about 15 microm and mammals as final hosts (Sarcocystis spp. of domestic animals and rodents) would be more significative. The second group can be subdivided into monoxenous species (Isospora), species with an optional intermediate host in which no or only slight multiplication occurs (Cystoisospora) and in genera with a multiplication in two phases in the intermediate host (Hammondia, Toxoplasma, Besnoitia). The nomenclature of single species is very controversial. As an example the controversial apprehension of the taxonomy of the Sarcocystis species of cattle is discussed. An application has been submitted to the International Commission for the Zoological Nomenclature to delcare a number of names as nomina dubia and to introduce unambiguous names for those organisms for which type specimens are available.
Cnidarians are generally considered to be the most primitive group of eumetazoans. They are therefore of considerable interest for comparative studies of metazoan development and evolution. The application of molecular techniques to cnidarians can provide important insights into developmental processes and phylogenetic relationships both within the phylum Cnidaria and among the eumetazoa. This paper reviews current knowledge of molecular and developmental biology of cinidarians with particular emphasis on tropical scleractinian corals and soft corals from the Great Barrier Reef region. Nucleotide sequencing of the histone gene cluster has unequivocally established that cnidarians are typical eumetazoans. Repeated sequence analysis has been applied to the staghorn corals, and implies a major divergence within this group, which corresponds with differences in sperm ultrastructure. Recent developmental studies of corals have indicated that some species have an unusual method of germ layer formation. Molecular events associated with this process, and with other important developmental stages, are currently under investigation. Other areas of current research interest, including targets for PCR-based investigations into cnidarian phylogeny, are highlighted.
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We have attempted to describe virtually all forms of malignant melanoma which affect man except those arising in the eye. The vast majority of malignant melanomas clearly fall into one of three kinds: (1) malignant melanoma of the superficial-spreading type, (2) malignant melanoma of the lentigo-maligna type, and (3) malignant melanoma of the nodular type. The developmental biology of a primary neoplasm is illustrated by discussing and illustrating the evolution of these three dominant forms of melanoma. Primary malignant melanoma of the superficial-spreading type and of the lentigo-maligna type develop through a characteristic biphasic growth pattern: an initial radial-growth phase, followed by a vertical-growth phase. The radial-growth phase of these melanomas is only rarely associated with the development of metastases, while the vertical-growth phase is commonly associated with subsequent metastatic disease. The phenomenon of the vertical-growth phase is apparently, therefore, a qualitative step in the development of a primary malignant melanoma. Malignant melanoma of the nodular type is an example of a primary tumor without a precursor developmental stage such as a radial-growth phase.
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Clinical experimental research on schizophrenia does not consider maturation processes of brain function in the majority of cases. In the course of neuronal organization and the differentiation phases of cerebral systems, early traumas in functionally important regions of the brain are accompanied by a facultative impairment of complex systems of information processing. Against the background of the comprehensively coherent "integrative psychobiological model of schizophrenia" (Ciompi) with high construct validity, (experimental) psychology investigations are reported on in the context of the "high-risk" concept in 44 young (20-37 years old) and mainly chronic schizophrenic patients with formation of a specific hypothesis for the developmental biology of the condition. In two homogeneous groups with the same structure, it is checked whether a discriminative appraisal concerning a different organization principle of central information processing systems is possible with "crossmodal" choice-reaction times (cCRT) and certain subscales of the Frankfurt symptom questionnaire (FBF) with regard to alternatively distributed and specially operationalized anamnestic biological risk factors. It can be objectively established in terms of experimental psychology that postpsychotically de-actualized "risk-free" schizophrenics differ from the reference group with a high-risk anamnesis in terms of significantly prolonged cCRT, but not from healthy subjects and an "MBD" control group. In addition, the FBF subscores "weakness of selective attention" and "loss of automatized skills" correlate with poor cCRT.(ABSTRACT TRUNCATED AT 250 WORDS)
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