In situ transcription and detection of CD 1a mRNA in epidermal cells: An alternative to standard in situ hybridization techniques

mRNA structure, in situ, as assessed by microscopic techniques

The secondary and tertiary structure of RNA, in situ, is thought to be involved in distinct functions such as directing association of the RNA with the cytoskeleton, enzymatic activity of some RNAs, and the control of translation. In situ transcription (IST), a procedure by which cDNA is synthesized in situ, has been used to assess mRNA structure in situ using fixed cells or tissues. Distinct banding patterns were noted for mouse and rat POMC. Unique IST banding patterns were observed when an oligonucleotide complementary to a putative POMC stem-loop structure was used to prime IST. Indeed local changes in banding patterns could be elicited by pharmacological agents which modulate POMC translation. Inhibition of POMC synthesis with NaF or dexamethasone decreased the number of POMC mRNAs in the polysome fractions and increased the intensity of high molecular weight IST-derived bands. Forskolin, a stimulator of POMC synthesis, had the opposite effect. One mechanism by which translational control is thought to occur is by regulation of ribosome movement down the mRNA by specific binding of cytosolic proteins to RNA structure. Cytosolic protein fractions from AtT20 pituitary cells have been shown to specifically bind to the IST-predicted RNA structure. These findings suggest that 1) mRNA structure can be assessed in situ, 2) translation may be altered by the secondary and tertiary structure of mRNAs, and 3) a predicted stem-loop structure exists in situ in the 5'-end of POMC mRNA.

Isolation of high quality mRNA from a discrete cell cycle population identified using a nonvital dye and fluorescence activated sorting

Flow cytometry (FCM) is useful for measuring DNA content as related to cell cycle position. We have extended this technology by developing a method that measures cellular DNA content using propidium iodide after permeabilization with lysolecithin. This technique maintains cell integrity such that high quality mRNA can be isolated from a sorted population. Unfixed MDA-468 cells, a human breast cancer cell line, were temporarily permeabilized with lysolecithin. A range of lysolecithin concentrations were studied in order to optimize DNA staining but minimize alterations in cell size and integrity. Cells permeabilized with lysolecithin in PBS, were stained with propidium iodide (50 micrograms/ml) in the presence of 1% bovine serum albumin, 1 mM Na2EDTA in PBS. The optimal concentration (4 micrograms lysolecithin/ml) combined staining approximately 90% of the cells for DNA, with minimal effects on cell size. Subsequently, the cells were assayed for DNA content as a measure of cell cycle position. MDA-468 cells identified as being in G1 were sorted and collected. From these, high quality mRNA could be isolated, as judged by its ability to be in vitro translated into protein of a wide range of molecular weights. This technique should be useful for molecular studies requiring discrete cell populations based on DNA content and/or cell cycle position.