Mitotic Segregation of the Nucleolar Ribosomal RNA in Physarum polycephalum

In the naturally synchronous mitosis of the syncytial plasmodium of Physarum polycephalum , the nucleolus disintegrates in prophase, releasing a large amount of ribosomal RNA. Using biotinylated rDNA probes, we studied by high-resolution in situ hybridization the behavior of this nucleolar RNA throughout mitosis. Our results demonstrate that this rRNA is stable and maintained within the mitotic nucleus mainly, but not exclusively, associated with fibrillar nucleolar remnants. The distribution of these rRNA molecules on both sides of the cleavage plane in telophase is indicative of a precise mechanism of mitotic partition of the nucleolar components, supporting our recent findings concerning the rDNA minichromosomes (Puvion-Dutilleul and Pierron, 1992, Exp. Cell Res. 203, 354-364). Taking advantage of the stability of this RNA component in mitosis, we unambiguously demonstrate that the nucleolar remnants are the precursors of the prenucleolar bodies appearing in the newly divided nuclei which, by fusion, reconstitute a single nucleolus. Our data exemplify the persistence of the nucleolar rRNA in mitosis and demonstrate that in Physarum, following its disintegration, the nucleolus is segregated and inherited.     

A case of congenital non-spherocytic hemolytic anemia caused by triose phosphate isomerase deficiency. Prenatal diagnosis

Prenatal diagnosis: The authors present a personal case of triose-phosphate-isomerase deficiency. Clinically the deficiency associates a constitutional non spherocytic anemia, paroxystic and precocius, and neuromuscular symptoms (axial hypotonia and limb palsies). A diaphragmatic paralysis may complicate the syndrome. Infections are frequent. Survival rarely goes beyond 5 years of age. Biochemical exams show the ubiquity of the deficiency. The physiopathology remains obscure. The TPI deficiency is heritable (autosomal recessive transmission). The gene has been mapped on the short arm of the chromosome 12. Prenatal diagnosis is possible.     

Metal-binding sites in germinating fern spores (Onoclea sensibilis)

Summary During germination of the spore of the sensitive fernOnoclea sensibilis L. the nucleus migrates from a central position to the proximal face and then to one end of the ellipsoidal spore. An asymmetric cell division follows giving rise to a small cell which differentiates immediately into a rhizoid, and a large cell which divides further to give rise to the prothallus. The proximal face of the spore coat is differentiated from the remainder of the spore by its ability to bind nickel ions under certain conditions and by its staining with a sulfide-silver procedure which localizes heavy metals. The inner portion of the exine at the proximal face is differentiated from the outer part by its ability to stain with sulfide-silver at specific periods during germination. The exine at the proximal face also contains pore-like structures 50 nm in diameter which extend from the inner layer of the exine to the outer surface. Sulfide-silver staining material appears to be extruded through the pores at specific periods during germination. The percentage of spores showing nickel-binding and sulfide-silver stainability increases sharply during the first two to four hours of imbibition, then decreases sharply during the following two hours. This is followed by a second rise in staining at 8 to 12 hours of imbibition.The role of the ion-binding sites in the exine is discussed in relation to the stable polarity of the spore.Publishing prior to 1984 asAlix R. Bassel