Search

Survival after gamma irradiation (generated from either a 137Cs or 60Co source) was determined for two strains of the nematode Caenorhabditis elegans. Animals were between 1.3 and 39 times more sensitive to cesium than to cobalt. The magnitude of this differential sensitivity was dependent upon the strain, developmental stage and sex tested. Several control experiments eliminated trivial explanations for this difference. Since cobalt- and cesium-generated gamma particles have nearly identical energy depositions, the differential sensitivity likely reflects different mechanisms of processing the slightly different spectra of DNA damage induced by these two radiations. Sex-specific differences in radiation sensitivity were also noted and were likely due to the fact that males possess a single X chromosome rather than two, as do hermaphrodites.

In Caenorhabditis elegans , loss of viability and fertility is observed after treatment with DES. The decrease in life span is associated with senescent morphology of meiotic prophase nuclei, such that nuclei from young and old specimens cannot be differentiated. Aging in oocytes at the pachytene stage of meiotic prophase is manifested by nucleo-cytoplasmic aberrations, increased density of the nucleoplasm and cytoplasm and decrease in numbers of mitochondria. Increasing concentrations of DES are characterized by concomitant decrease in fertility and increased production of abnormal gametes. At DES concentrations higher than 1.25 μg/ml, synaptonemal complexes (SC) are absent from the nuclei, thus, effective pairing and segregation of homologous chromosomes is not possible. The absence of SCs may be the result of: (1) a premeiotic colchicine-like effect that influences pairing of chromosomes; (2) changes in the structure of the DNA due to DES binding that results in changes in expression of the DNA; and (3) changs in temporal DNA synthesis in response to DES. Since the SC is essential for regulating pairing and subsequent separation of bivalents, the lack of an SC explains the loss of fertility, due to the production of unbalanced gametes, observed in DES-treated specimens.

A technique for the extraction of pure somatic (post-diminution) and germ line (pre-diminution) DNA from the parasitic nematode Ascaris is described. Uncontaminated post- and pre-diminution DNAs were sheared and reassociated to different C0t values. Computer analysis of the complete reassociation kinetics determined that 33% of the germ line genome is eliminated during the process of chromatin diminution. The eliminated DNA is comprised of repetitive and unique sequences in an approx. 1:1 ratio.

An information feedback model and an ideology of evaluation is posed. The authors' experiences in actually doing evaluation research are then contrasted with the model and ideology. Suggestions are made for closing the gap between reality and the model, primarily by altering the structural constraints that present obstacles to achieving the model. The authors assume that impact on policy is the appropriate criterion for the success of an evlauation, and they conclude that political constraints are primary in preventing evaluation research from having this impact. It is proposed that evaluators need to develop more explicitly political ways of acquiring power of their own in order to maximize such impact. Some ways social researchers might conceptualize and construct an appropriate base of power are considered.

In the rad -4 mutant of C. elegans there is a specific increase in the number of ‘Disjunction Regulator Regions’ (DDR) present on the synaptonemal complexes (SC) in pachytene nuclei. These DDRs either promote disjunction or inhibit nondisjunction of the X-chromosome as evidenced by the 10-fold decrease in the rate of X-chromosome nondisjunction as compared to the wild-type. The structure of the tripartite SC is normal, thus, the decrease in the rate of X-chromosome nondisjunction in the rad -4 mutant is not related to the structure of the SC but may be related to the number of DDRs. Other changes are also associated with the sensitivity to irradiation, i.e. the pachytene nuclear morphology is altered such that nuclei and nucleoli are 50% the size of wild-type. In addition, the autosomal: X-chromosome size ratio is reduced in the rad -4 mutant. That there are six SCs confirms n = 6 in this mutant and of these six SCs three can be identified: (1) the XX bivalent, SC No. 1, is the shortest and pairs synchronously with the autosomes; (2) the longest bivalent, SC No. 6, carries the nucleolar organizer region at one extreme end; and (3) SC No. 5 has two DDRs located approximately on μm apart from each other.

A 3,780-g newborn girl had multiple, bilateral eyelid adhesions taht connected the upper and lower eyelids by bands of extensile tissue. Although the eyelid lesion was benign, the associated systemic abnormalities may have been serious. We doubt that a single intrauterine insult led to ankyloblepharon filiforme adnatum and the associated anomalies.