Summary. Megakaryocytes have been studied in rats using objective methods, with assessment of numbers of cells, cell diameter and DNA content. Stimulation and suppression of platelet production have been shown to be accompanied by changes in cell diameter, and in numbers of megakaryocytes in the bone marrow and spleen. A method is described permitting measurement of DNA content of the cells under these conditions, using Feulgen staining and an integrating micro‐densitometer. It has been demonstrated that alteration in size is secondary to alteration in ploidy value. The reduction in ploidy following transfusion of platelets was apparent morphologically as a decrease in the number of lobes in the nucleus, but following stimulation of platelet production, an increase in ploidy occurred which was not associated with a discernible increase in nuclear lobulation. Microdensitometry provides the only certain method of objective assessment of megakaryocyte ploidy. It is concluded that the system regulating megakaryocyte proliferation governs DNA replication in both megakaryoblast and stem cells.

Gene expression analysis at the single-cell level is critical to understanding variations among cells in heterogeneous populations. Microfluidic reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) is well suited to gene expression assays of single cells. We present a microfluidic approach that integrates all functional steps for RT-qPCR of a single cell, including isolation and lysis of the cell, as well as purification, reverse transcription and quantitative real-time PCR of messenger RNA in the cell lysate. In this approach, all reactions in the multi-step assay of a single lysed cell can be completed on microbeads, thereby simplifying the design, fabrication and operation of the microfluidic device, as well as facilitating the minimization of sample loss or contamination. In the microfluidic device, a single cell is isolated and lysed; mRNA in the cell lysate is then analyzed by RT-qPCR using primers immobilized on microbeads in a single microchamber whose temperature is controlled in closed loop via an integrated heater and temperature sensor. The utility of the approach was demonstrated by the analysis of the effects of the drug (methyl methanesulfonate, MMS) on the induction of the cyclin-dependent kinase inhibitor 1a (CDKN1A) in single human cancer cells (MCF-7), demonstrating the potential of our approach for efficient, integrated single-cell RT-qPCR for gene expression analysis.