Organization of giant interneuron projections in thoracic ganglia of the cockroach Periplaneta americana

We have investigated the structural organization of the wind-sensitive giant interneurons in the thoracic ganglia of adult American cockroaches. These seven bilaterally paired interneurons have long been thought to play a role in directing the wind-elicited escape response of the animal. Each of the giant interneurons was labeled individually by intracellular injection of cobaltic hexamine chloride. An individual giant interneuron could be reliably identified from animal to animal based on its branching pattern in thoracic ganglia. The axons of the giant interneurons are situated on each side of the nerve cord in two recognizable subgroups. Comparisons of the axonal arbors of the dorsal and ventral subgroups showed that they project into distinct but partly overlapping regions of thoracic ganglia. Three of the giant interneurons were found to have axonal arbors that cross the longitudinal midline of thoracic and abdominal ganglia. Bilateral pairs of these giant interneurons were labeled concomitantly, and many of the individual neurites from these cells appeared to be closely apposed. All these morphological characteristics are discussed in relation to the connectivity and functional significance of the giant interneurons.     

Citreoviridin levels in Eupenicillium ochrosalmoneum-infested maize kernels at harvest

Citreoviridin contents were measured in eight bulk samples of maize kernels collected from eight fields immediately following harvest in southern Georgia. Citreoviridin contamination in six of the bulk samples ranged from 19 to 2,790 micrograms/kg. In hand-picked samples the toxin was concentrated in a few kernels (pick-outs), the contents of which were stained a bright lemon yellow (range, 53,800 to 759,900 micrograms/kg). The citreoviridin-producing fungus Eupenicillium ochrosalmoneum Scott & Stolk was isolated from each of these pick-out kernels. Citreoviridin was not detected in bulk samples from two of the fields. Aflatoxins were also present in all of the bulk samples (total aflatoxin B1 and B2; range, 7 to 360 micrograms/kg), including those not containing citreoviridin. In Biotron-grown maize ears that were inoculated with E. ochrosalmoneum through a wound made with a toothpick, citreoviridin was concentrated primarily in the wounded and fungus-rotted kernels (range, 142,000 to 2,780,000 micrograms/kg). Samples of uninjured kernels immediately adjacent to the wounded kernel (first circle) had less than 4,000 micrograms of citreoviridin per kg, while the mean concentration of toxin in kernel samples representing the next row removed (second circle) and all remaining kernels from the ear was less than 45 micrograms/kg. Animal toxicosis has not been linked to citreoviridin-contaminated maize.     

Endomitosis: A reappraisal

Summary The concept and role of endomitosis is reevaluated in the light of observations on three organisms. Endomitosis which morphologically agrees with Geitler's (1939) classical definition is compared in tapetal cells of the liliaceous plant Eremurus, in the septal cells of the testicular follicles of the grasshopper Melanoplus, and in human cells from normal and molar trophoblasts and cervical cancer. These observations, together with those of Kidnadze and Istomina (1980), show that functionally at least two fundamentally different types of endomitosis exist, although morphologically the stages resemble each other in the three organisms. In the first type, exemplified by Eremurus, each endomitosis leads to a chromosome constitution which represents one level higher ploidy, a course that has been assumed to be characteristic of endomitosis in general. The second type, observed in its most characteristic form in the grasshopper, seems to be stationary: no DNA synthesis occurs, but an intensive RNA synthesis takes place. Presumably such cells have reached a final state in their development and are specialized in manufacturing one or more gene products. Endomitosis in normal placenta comes near this type, although DNA synthesis takes place in occasional cells. However, similar endomitotic nuclei in the hydatiform moles are in the process of DNA synthesis. When endomitosis is analyzed in different organisms and tissues, the observation that this process is not one entity should be kept in mind.     

Effects of actinomycin D, amethopterin, and 5-fluro-2'-deoxyuridine on procentriole formation in Chinese hamster fibroblasts in culture

Synchronized Chinese hamster fibroblasts (Don-C) were cultured for 6 h in the presence of amethopterin, 5-fluorodeoxyuridine (FUdR), or actinomycin D and were then examined by electron microscopy of thin sections for the presence or absence of daughter procentrioles. Control cells were at mid S phase and contained obvious procentrioles in about 1 profile out of 140. Treatment with FUdR or amethopterin did not reduce this frequency significantly. However, serial section analysis did demonstrate a lack of procentrioles in some cells treated with amethopterin. Actinomycin was quite effective in preventing daughter procentriole formation.     

A theory for developmental control by a program encoded in the genome

A new genetic mechanism is proposed to explain the evident order seen in embryonic development. This theory postulates control DNA, a set of genetic elements activated in a specific sequence, one at a time. With each cell division, control of gene expression passes to the next control unit in the series. The complete series of control units would constitute the encoded (and inherited) development program of an organism.