We have isolated and characterized two human middle repetitive alphoid DNA fragments, L1.26 and L1.84, which localize to two different sets of chromosomes. In situ hybridization revealed both repeats to have major and minor binding sites on the pericentric regions of several chromosomes. Probe L1.26 maps predominantly to chromosomes 13 and 21. Probe L1.84 locates to chromosome 18. Minor hybridization sites for both probes include chromosomes 2, 8, 9, and 20; in addition, L1.26 revealed minor sites on chromosomes 18 and 22. The binding to these sites strongly depends on hybridization conditions. In Southern blot hybridizations to total human DNA, both L1.26 and L1.84 give the same ladder pattern, with a step size of 170 bp, indicating their presence as tandem repeats, but with different band intensities for each probe. The chromosome-specific nature of particular multimers was confirmed by Southern blot analyses of a human-rodent hybrid cell panel. We conclude that L1.26 and L1.84, with their related sequences, constitute subfamilies of alphoid DNA that are specific for subsets of chromosomes and, in some cases, possibly even for single chromosomes.

Acrosome-reacted spermatozoa were microinjected into the perivitelline space of mouse oocytes. After 2 h incubation in culture medium containing lactate and albumin, spermatozoa were transferred into culture medium containing 12 mM of dibutyryl cyclic guanosine 3',5'-monophosphate (dbcGMP) and 10 mM imidazole for 20 min. One motile spermatozoon was injected into the perivitelline space of each oocyte. Fertilization was recognized by the presence of a second polar body and two pronuclei. The overall fertilization rate was 19.6% in the case of dbcGMP-treated spermatozoa as compared to 5.3% for non-treated spermatozoa. Thus, acrosome-reacted motile spermatozoa improve the fertilization rate of sperm microinjection. Sperm microinjection may be a method to foster fertility in cases of oligo-/asthenozoospermia in human in-vitro fertilization.

The influence of age and sex on the behaviour and distribution of 9% and was investigated in albino rats after administration of solutions with eoSr-gOY in radioactive equilibrium. The ratio of Y/Sr, Q, was found to be proportional to age and was also significantly higher for female animals as compared to males. Sex and age acted additively, increasing the radioactive burden of the bones in the case of female animals substantially.

Modulation of radiosensitivity by components of the extracellular matrix (ECM) and cytoskeletal elements has not been adequately studied. Although differences in the radiosensitivities of cells grown as monolayers, as spheroids, or grown in vitro in animal models are known, explanations have in the past neglected possible influences by the ECM and cytoskeleton. Using collagen gel cultures, it is shown that the fibrillar component of the ECM (which is responsible for cell anchorage) induces shifts in radiosensitivity. The effect is critically dependent on the affinity of the cell type towards collagen. The shifts in radiosensitivity induced by ECM alteration are manifested as changed Dq values. By applying four specific cytoskeletal poisons which either stabilize or destabilize specific cytoskeletal elements, the involvement of microfilaments and microtubuli was qualitatively appraised. Cytochalasin B, which destabilizes microfilaments (by preventing polymerization), caused a significant rise in radioresistance. This rise was due to increased D0. Although the cellular morphological change accompanying cytochalasin B treatment was essentially similar to that obtained with trypsin, the respective shifts in radioresponses were qualitatively different and opposite, suggesting differences in mechanism of action.

By use of a rapid technique, initial rates of D-glucose transport were obtained during the lifespan in vitro of a commercially available strain of human embryo lung fibroblasts (Flow 2000). The apparent Km of the D-glucose carrier did not change during senescence in vitro: 8 = 1.8 mM (range 1.3-2.3) in phase 11, X = 1.8 mM (range 1.5-2.2) in phase 111. Transport rates remained constant in stationary phase I1 cultures, which had completed between 3Wo and 8Wo of their replicative lifespan. A wide variation, however, was observed in terminally differentiated cells (phase III), which showed a two-to threefold increase in average cell size and protein content. In some senescent cultures, glucose transport calculated on a per cell basis was also two-to threefold increased, while it was strongly decreased (-75%) in others. When calculated per unit of cell water, protein, and surface area, respectively, transport rates in phase I11 cultures ranged from values established for stationary phase I1 cultures down to very low values. Detaching cells flushed off from senescent cultures did not show measurable rates of glucose transport into the inulin impermeable cell space. Present evidence argues against the idea that an impairment of D-glucose transport might precede loss of replicative potential in aging human fibroblasts. Instead our data indicate that the transport capacity of cell membrane finally decreases during postreplicative senescence in terminally differentiated cells.