For coordinated circulation, vertebrate and invertebrate hearts require stereotyped arrangements of diverse cell populations. This study explores the process of cardiac cell diversification in the Drosophila heart, focusing on the two major cardioblast subpopulations: generic working myocardial cells and inflow valve-forming ostial cardioblasts. By screening a large collection of randomly induced mutants, we identified several genes involved in cardiac patterning. Further analysis revealed an unexpected, specific requirement of EGF signaling for the specification of generic cardioblasts and a subset of pericardial cells. We demonstrate that the Tbx20 ortholog Midline acts as a direct target of the EGFR effector Pointed to repress ostial fates. Furthermore, we identified Edl/Mae, an antagonist of the ETS factor Pointed, as a novel cardiac regulator crucial for ostial cardioblast specification. Combining these findings, we propose a regulatory model in which the balance between activation of Pointed and its inhibition by Edl controls cardioblast subtype-specific gene expression.
SumutayyUsing substrate tritiated stereospecifically a t C-6 it was shown that the dehydroshikimate dehydratase reaction involves the syn-elimination of the elements of water, whereas the acid-catalysed chemical conversion of 3-dehydroshikimate into protocatechuate proceeds nonstereospecifically and involves a hydrogen isotope effect.
D‐Shikimic acids 1−14C, 6−14C and 7‐(carboxyl) 14C have been biosynthetically prepared with specific activities of about 25 mCi/mmole and with overall yields of 45% based on pyruvate 3,2 or 1−14C as the respective starting materials. A crude cellfree homogenate of E. coli 83–24 was used to catalyze the condensation of phosphoenolpyruvate−14C with unlabelled erythrose‐4‐phosphate to give shikimic acid. Phosphoenolpyruvate−14C was synthesized from pyruvate−14C and ATP by the action of phosphoenolpyruvate‐synthase. Erythrose‐4‐phosphate 1,2,3,4−14C and erythrose‐4‐phosphate‐4‐T was prepared from glucose‐U−14C and glucose‐6‐T via enzymatic phosphorylation to labelled glucose‐6‐phosphate and subsequent lead tetraacetate oxidation. Condensation of labelled E‐4‐P with unlabelled PEP gave rise to shikimic acid‐2,3,4,5−14C and 2‐T.
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