Mitochondria and polarity in the egg ofSmittia spec. (Diptera, Chironomidae): UV irradiation, respiration measurements, ATP determination and application of inhibitors

Induction and the Turing-Child field in development

The central problem in biological development is the understanding of epigenesis. The dominant theory of development in the last 80 years that also purports to explain epigenesis is induction theory. It suggests that development is driven by sequential inductions where each "induction" (in one sense of the word induction) is effected by the action of an inducing part of the embryo on a responding part of the embryo. The theory stems from Spemann and Mangold (W.Roux' Arch.f.Entw.d.Organis.u.mikrosk.Anat.100 (1924) 599) who transplanted a tissue from the dorsal blastopore lip of Triturus into the ventral ectoderm of another gastrula and thus initiated and "induced" (in another sense of the word induction) gastrulation and embryogenesis in the ventral side of the host that became a double embryo (siamese twins). We explain this induction, i.e. the formation of the double embryo, according to the Child theory and the Turing-Gierer-Meinhardt theory when it is also assumed that cAMP and ATP are the Turing activator and inhibitor, respectively. Spemann and Mangold (W.Roux' Arch.f.Entw.d.Organis.u.mikrosk.Anat.100 (1924) 599) also suggested that the ingressing mesoderm induces the overlying ectoderm to form the neural plate and neural tube. This 'neural induction', the 'primary embryonic induction', became the cornerstone of induction theory, i.e. of the sequential induction concept referred to above. But we argue that the metabolic gradients that precede and accompany neurulation, as obtained by Child, also for Triturus, arise through a Turing self-organization if it is assumed that cAMP and ATP are the Turing morphogens, and these gradients are the cause and primary event of neurulation. Thus there is no need to invoke the 'neural induction'. It is argued that fundamental events such as gastrulation and also organ formation are caused by the Turing-Child field and not by sequential induction. Similar principles, such as bud formation caused by a radial metabolic pattern that transforms to a longitudinal pattern, govern the formation, for example, of the mouth and the gut. The formation and localization of bottle cells is explained according to the Child-Turing field and modern biochemistry. The chemical metabolic pre-pattern precedes, and causes, morphogenesis and differentiation as envisaged by Turing. The Spemann and Mangold (W.Roux' Arch.f.Entw.d.Organis.u.mikrosk.Anat.100 (1924) 599) transplantation experiment when performed on a sea urchin duplicates not only the phenotype but also the metabolic (reduction) pattern. These experimental results, by Horstadius, predicted by Child, follow from the Turing-Gierer-Meinhardt theory if it is assumed that cAMP and ATP are the Turing morphogens. If the transplantation is performed not onto the whole sea urchin but onto only a part of it, that manifests only a part of the metabolic pattern, then from the part a phenotypic whole underlain by a normal and a whole metabolic pattern can be rescued. These experimental results of Horstadius follow from Turing theory if cAMP and ATP are the Turing morphogens. Understanding how to transform a part into a whole can be valuable in regenerative medicine. Unspecific induction of a secondary amphibian embryo is similar to the induction of posterior structures at the anterior pole of an insect, and the "double abdomen" (and Kalthoff's experimental results) of the midge Smittia resulting from UV irradiation of the anterior pole, can be explained by Meinhardt theory of unspecific induction if ATP is the Turing morphogen. When not working on regeneration, Child investigated intact living organisms and his observation method was not disruptive to normal development, whereas workers in induction theory work with pieces and in general disrupt normal development. We conclude that the Turing-Child field causes all development and explains epigenesis. Sequential induction does not explain epigenesis and does not exist in normal development. But induction in the sense of a transplantation leading to double embryo or rescuing a whole phenotype from a part is of interest.

Unusual distribution of mitochondrial large subunit rRNA in the cytosol during conjugation in Tetrahymena thermophila

The distribution of mitochondria during conjugation of the ciliated protozoan Tetrahymena thermophila was surveyed using a mitochondrial stain and fluorescence in situ hybridization (FISH). When the mitochondria-specific stain, Mito-Tracker, was used, the majority of mitochondria were detected in the cortex; their distribution was not changed during conjugation. On the other hand, FISH using mitochondrial large subunit (LSU) rRNA as a probe showed an unusual distribution of signals during conjugation. Unexpectedly, the signals were detected throughout the cytoplasm of conjugating cells. These signals were not observed in pre-mating cells and in exconjugants. The cytosolic localization of mitochondrial rRNA was supported by northern blot analysis using post-mitochondrial RNA fraction at the later stages of conjugation. These observations suggest selective mitochondrial breakdown or transport of LSU rRNA into cytosol. The biological significance of the conjugation-specific appearance of the cytosolic mitochondrial rRNA is discussed.

Abortive conjugation induced by UV-B irradiation at meiotic prophase in Tetrahymena thermophila

Conjugating Tetrahymena were irradiated by ultraviolet-B (UV-B) at various stages of conjugation. When the conjugants were exposed to the UV-B at late meiotic prophase (the stage from pachytene to diplotene), abortive conjugation was induced a high frequencies. After completing meiosis, a significant number of the conjugants showed marked anomalies, i.e., failure of nuclear selection after meiosis, and abortion of the subsequent conjugation process such as a postmeiotic division to form gametic nuclei, nuclear exchange, synkaryon formation, and postzygotic development. The conjugating pairs retained the parental macronucleus and separated earlier as compared with a control. The resultant exconjugants degenerated meiotic products and became amicronucleates. These observations strongly suggest the presence of a UV-sensitive molecule that is expressed specifically at the meiotic prophase and that directs the subsequent development after meiosis.

Functions of maternal mRNA as a cytoplasmic factor responsible for pole cell formation in Drosophila embryos

Injection of mRNA extracted from Drosophila cleavage embryos or mature oocytes restored pole cell-forming ability to embryos that had been deprived of this ability by uv irradiation. However, mRNA extracted from blastoderms did not show the restoration activity. Pole cells thus formed in uv-irradiated embryos bear similarities to normal pole cells both in their morphology and their ability to migrate to the gonadal rudiments. But this mRNA does not appear to be capable of rescuing uv-induced sterility, or inducing pole cells in the anterior polar region.