Fig. 4. RT-PCR analysis of CD45 expression within CD34⁺ CD45⁺ (+/+), CD34⁺ CD45^– (+/–) and CD34^– CD45^– (–/–) cell subsets sorted from the human embryo. mRNA was extracted from CD34⁺ CD45^– cells sorted from the 32-day yolk sac and 32-day AGM and from CD34⁺ CD45⁺, CD34⁺ CD45^– and CD34^– CD45^– cells sorted from the 40-day embryonic liver. mRNA was also extracted from the whole (W) yolk sac, AGM and embryonic liver. mRNAs were then retro-transcribed into cDNAs and CD45 cDNAs were amplified by PCR. Amplified products were separated on a 1.5% agarose gel and visualized after BET staining. Product size was checked by running molecular weight markers. Signals obtained for ß-actin cDNA amplification were used as references to normalize differences between cDNA samples.