Two recombinant DNA clones that are localized to single human chromosomes were isolated from a human repetitive DNA library. Clone pHuR 98, a variant satellite 3 sequence, specifically hybridizes to chromosome position 9qh. Clone pHuR 195, a variant satellite 2 sequence, specifically hybridizes to chromosome position 16qh. These locations were determined by fluorescent in situ hybridization to metaphase chromosomes, and confirmed by DNA hybridizations to human chromosomes sorted by flow cytometry. Pulsed field gel electrophoresis analysis indicated that both sequences exist in the genome as large DNA blocks. In situ hybridization to intact interphase nuclei showed a well-defined, localized organization for both DNA sequences. The ability to tag specific human autosomal chromosomes, both at metaphase and in interphase nuclei, allows novel molecular cytogenetic analyses in numerous basic research and clinical studies.

The cell differentiation of HL-60 human leukemic promyelocytes along the myeloid pathway due to various continuous and distributed exposures to retinoic acid was studied. HL-60 myeloid differentiation was a continuously driven process; significant terminal cell differentiation occurred only after a minimum exposure to inducer of two division cycles. Cells so committed to differentiation retained a heritable, finite memory of differentiation commitment over a further division cycle. Prior to becoming committed, cells acquired precommitment memory of exposure to inducer. Precommitment memory abbreviated the subsequent exposure to inducer needed for commitment to differentiation. Precommitment memory was semistable. It was heritable, but was lost after four division cycles. The acquisition and loss of precommitment memory correlated with alterations in nuclear architecture detected by narrow angle light scatter using flow cytometry. The altered nuclear architecture first occurred before any overt cell differentiation or growth arrest. It was thus an early event in the induced program of terminal cell differentiation. Alterations in relative abundances of cytoplasmic proteins also occurred prior to overt cell differentiation or growth arrest. One of these was a 17 kdalton, anionic, probably Ca2+ binding, protein. Retinoic acid thus induced early cellular changes, including cytoplasmic and nuclear alterations, within one cell cycle when cell differentiation was not yet apparent.

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In a recent paper a new technique was proposed for remote ranging and topographical mapping by using a system with a single-photon-counting detector and a low-power pulsed laser ͓Appl. Opt. 35, 441 ͑1996͔͒. We report on the results from the laboratory and the field demonstration of this literal three-dimensional imaging technique. Using a detector system developed at Los Alamos with a commercial pulsed laser and observing from a single remote vantage point, we demonstrate use of this technique in the literal mapping of three-dimensional topography and the probing of a complex scene. With a reasonably short exposure this system can resolve features with height variations as small as 5 cm.

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