WI-38 and SV40WI-38 cells have been synchronized using centrifugal elutriation . This technique allows for the rapid harvesting of early G, phase cells from exponentially growing populations of both the normal and transformed cell. Using these cells, as well as WI-38 cells synchronized by serum deprivation, we have examined the effects of extracellular Ca and Mg levels on the progression of cells through GI phase . A differential sensitivity to both Ca and Mg deprivation is observed between normal and transformed cells. The WI-38 cell requires higher levels of both ions for traversal of G, phase and for continued proliferation as compared to the transformed cell. The temporal nature of the Ca and Mg requirements for the WI-38 cell has been examined during G, phase . Ca is strictly required during early and late G, phase, but not necessarily throughout mid-G, .

Neurobehavioral correlates of CGG amplification were studied in 17 nonretarded adult female carriers of fragile X syndrome. The results revealed a significant relationship between IQ and the number of CGG repeats in the 5' untranslated region of the FMR1 gene. Women with a full mutation (> 200 CGG repeats) scored below average in IQ, visual-spatial perception, visual-spatial organization, and executive function. There were no differences in fine motor dexterity or memory as a function of CGG amplification status. A history of major depressive disorder was identified in 71% of the sample, but incidence of depression was not associated with the degree of CGG amplification. Schizotypal features were noted in 18%. No intellectual or neuropsychological deficit was found in women with a premutation (< 200 CGG repeats). Decrements in IQ, visual-spatial perception, and executive function appear to arise as a consequence of the CGG amplification.

Serum stimulation of quiescent 3T3 cells returns the cells to a proliferative state. Changes in Ca content, transport and distribution during the transition through G1 and S phase have been investigated following serum stimulation of these cells. 45 Ca exchange data indicate at least two kinetically defined cellular compartments for Ca; a rapidly exchanging component presumably representing surface Ca which is removable by EGTA and a slowly exchanging component presumably representing cytoplasmically located Ca. Previous studies (Tupper and Zorgniotti, '77) indicate that the approach to quiescence in the 3T3 cells is characterized by a large increase in the surface Ca component. The present data demonstrate that this component is rapidly lost following serum stimulation. Furthermore, the serum induces an 8-fold increase in Ca influx into the cytoplasmic compartment and a reduction in the unidirectional efflux rate coefficient for Ca. The increased Ca uptake peaks at approximately six hours (mid G1) and is accompanied by a parallel increase in cellular Ca. Prior to entrance of the cells into S phase (10-12 hours), Ca uptake declines. This is followed by a slower decline in cytoplasmic Ca levels. Simultaneous addition to fresh serum plus 0.5 mM dibutryl cAMP inhibits the entrance of the cells into S phase. Under these conditions the loss of surface Ca is not blocked. However, the presence of 0.5 mM dibutyryl cAMP inhibits the increase in Ca uptake and, in turn, diminishes the increase in cellular Ca following serum stimulation. In contrast, a low level of dibutyryl cAMP (0.1 mM) enhances progression through G1 phase but also reduces both Ca uptake and Ca content of the cells. The data suggest that the serum induced changes in Ca content and transport are linked to intracellular cyclic nucleotide levels and progression through G1 phase and that extracellular cAMP elevating agents may enhance of inhibit these interactions in a concentration dependent manner.

The kinetics of Ca ++ uptake have been evaluated in 3T3 and SV40-3T3 mouse cells. The data reveal at least two exchangeable cellular compartments in the 3T3 and SV40-3T3 cell over a 50-min exposure to *~Ca ++. A rapidly exchanging compartment may represent surface-membrane-localized Ca ++ whereas a more slowly exchanging compartment is presumably intracellular. The transition of the 3T3 cell from exponential growth (at 3 day's incubation) to quiescence (at 7 days) is characterized by a 7.5-fold increase in the size of the fast component. Quiescence of the 3T3 cell is also characterized by a 3.2-fold increase in the unidirectional Ca ++ influx into the slowly exchanging compartment and a 3.6-fold increase in its size. The increase in size of the slow compartment at quiescence may result from a redistribution of intracellular Ca ++ to a more readily exchangeable compartment, possibly reflecting a release of previously bound Ca ++. In contrast, no significant change in any of these parameters is observed in the proliferatively active SV40-3T3 cells after corresponding periods of incubation, even though these cells attained higher growth densities and underwent postconfluence.

GC3/c1 human colon adenocarcinoma cells were treated with the mutagen ethyl methanesulfonate, and three clones deficient in thymidylate synthase (5,10-methylenetetrahydrofolate:dUMP C-methyltransferase, EC 2.1.1. 45) activity were selected and characterized. Growth in medium deficient in thymidine caused cell death in two clones (TS-cl and TS-c3), whereas one clone (TS-c2) showed limited growth.Growth correlated with thymidine synthase activity and 5-fluoro-2'-deoxyuridine 5'-monophosphate-binding capacity and with incorporation of 2'-deoxy[6-3H]uridine into DNA. In the presence of optimal thymidine, growth rates were only 5-18% that of the parental clone (GC3/cl), which grew equally well in thymidine-deficient or -replete medium. Analysis of poly(A)+ RNA showed normal levels of a 1.6-kilobase transcript in TS-cl and TS-c2 but decreased levels (=6% control) in TS-c3. Clone TS-c3 was 32-, 750-, and >100,000-fold more resistant than the parental clone to 5-fluorouracil, 5-fluoro-2'-deoxyuridine, and methotrexate, respectively. When inoculated into athymic nude mice, each TS-clone produced tumors, demonstrating continued ability to proliferate in vivo.