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Figure 4. Localization of Hematopoietic Precursors in the Region of the Dorsal Aorta and Their Origins (A) In situ hybridization on 10 um sections reveals expression of GATA-2 (a and b), SCL (c), Xaml (d), and GATA-3 (e) in the region of the dorsal aorta of stage 43 embryos. Notice that both GATA-2 and Xaml are expressed in clusters within the dorsal aorta, in the ventral wall of the dorsal aorta, and in mesenchymal cells below the dorsal aorta. SCL is mainly expressed in the ventral wall of the dorsal aorta and in clusters within the aorta. GATA-3 is expressed in the pronephric ducts only. GATA-2, SCL, and Xaml expression are not detected in circulating blood cells at this stage of development (data not shown). All sections are transverse. Red arrows indicate expression in the ventral wall of the dorsal aorta and in mesenchyme below the aorta. Red arrowheads indicate the endothelial lining of the dorsal aorta. Black arrowheads indicate the pronephric ducts. n, notochord; sc, spinal cord; s, somites. (B) Detection of beta-galactosidase activity at stage 43 in C3 beta-gal injected embryos. (a) location of beta-galactosidase in a stage 43 embryo which was injected with beta-gal RNA in the C3 blastomere at the 32-cell stage. Note that beta-gal is not detected in the heart, gills, and tail vessels (TV) where circulating blood cells are easily detected, indicating that C3 does not contribute to the primitive blood. (b) Ten micrometer transverse section of another C3 embryo at the A/P level of the single median dorsal aorta (just posterior to the glomus). (c) Same section magnified. Red arrowheads indicate the endothelial lining of the dorsal aorta. Red arrows indicate beta-gal positive mesenchymal cells located just ventral to the dorsal aorta. Black arrowheads indicate pronephric ducts. beta-gal positive cells are also located further anterior in the paired dorsal aortae, pronephros, and the glomus (data not shown). n, notochord; s, somites; sc, spinal cord; PD, pronephric ducts; PN pronephros; TV, tail vessels. |
