In situ hybridization to chromosomes stabilized in gel microdrops

Use of fluorescent sequence-specific polyamides to discriminate human chromosomes by microscopy and flow cytometry

In this paper, we demonstrate the use of synthetic polyamide probes to fluorescently label heterochromatic regions on human chromosomes for discrimination in cytogenetic preparations and by flow cytometry. Polyamides bind to the minor groove of DNA in a sequence-specific manner. Unlike conventional sequence-specific DNA or RNA probes, polyamides can recognize their target sequence without the need to subject chromosomes to harsh denaturing conditions. For this study, we designed and synthesized a polyamide to target the TTCCA-motif repeated in the heterochromatic regions of chromosome 9, Y and 1. We demonstrate that the fluorescently labeled polyamide binds to its target sequence in both conventional cytogenetic preparations of metaphase chromosomes and suspended chromosomes without denaturation. Chromosomes 9 and Y can be discriminated and purified by flow sorting on the basis of polyamide binding and Hoechst 33258 staining. We generate chromosome 9- and Y-specific 'paints' from the sorted fractions. We demonstrate the utility of this technology by characterizing the sequence of an olfactory receptor gene that is duplicated on multiple chromosomes. By separating chromosome 9 from chromosomes 10-12 on the basis of polyamide fluorescence, we determine and differentiate the haplotypes of the highly similar copies of this gene on chromosomes 9 and 11.

Gel microdrop technology for rapid isolation of rare and high producer cells

Secreted proteins are a therapeutic cornerstone of the biotechnology industry, and numerous recombinant products, including human growth hormone, human erythropoietin and granulocyte-colony stimulating factor, are now widely prescribed. In addition to bioprocessing applications, GMD technology should benefit the emerging fields of cellular and gene therapy. The ability to assess rapidly and precisely the productivity of cells for ex vivo cell screening and expansion is a unique approach with numerous research and therapeutic uses.

FACS-based isolation of slowly growing cells: double encapsulation of yeast in gel microdrops

Isolating hyperproducing cells is important in biotechnology, but these cells usually grow slowly and can be overgrown by poorly producing cells. We describe a new method of isolating slowly growing cells from among rapidly growing cells, which has the potential for automation and high throughput (e.g., 100,000 cells/h). A model system is presented consisting of a mixed population of slowly growing mutant and rapidly growing wild-type yeast, which were encapsulated in double agarose gel microdrops (dGMDs); with most dGMDs initially containing single cells. Double encapsulation locates parent cells near dGMD centers, making microcolony measurement more accurate. After a 15-h incubation, fluorescent activated cell sorting was used to analyze and sort dGMDs with small microcolonies (slow growers) from dGMDs with large microcolonies (rapid growers). Successful isolation of slow growers from a mixed population of predominantly rapidly growing Saccharomyces cerevisiae cells was achieved.