Master's Thesis from the year 2007 in the subject Biology - Zoology, grade: 1,0, University of Innsbruck (Zoologie), language: English, abstract: The transcription factor GATA-1 is essential for the development of the erythroid cell lineage in vertebrates. In this article we introduce a method to easily determine the approximately development status of red blood cells and the progression of blood formation by intensity of fluorescence in GATA-1/Ds-Red marked zebrafish. We classified the blood cells on the basis of their fluorescence intensity in 5 intensity stages (IS) with the brightest in IS 1. The comparison with our erythropoietin (Epo) data showed a noticable correlation between GATA-1, Epo mRNA and EPO protein level. Between 2 and 3 dpf we observed a major increase in blood cell concentration to circa 1200 cells*nl-1, until 15 dpf this value decreased to about the half. The appearance of IS 1 cells correspond approximately to the peaks in Epo cRNA copies and the highest values in EPO protein emerged about 1 day later. Our data show that the blood cell concentration, Epo and Gata-1 expression in zebrafish larvae is subjected to large fluctuations in the first few days of development.