Expression tinman

Initial tinman expression occurs at cellular blastoderm in the prospective mesoderm and is confined to the trunk mesoderm where it is initally modulated in a peri-t)dic pair-rule pattern (Bodmer et ah, 1990 Azpiazu and Frasch. 1993). During invagination and dorsal migration of the mesoderm, the entire trunk mesoderm expresses tinman mRNA in a uniform pattern. However, shortly before the mesoderm reaches the dorsal border of the ectoderm, tinman expression decreases in the ventral portions and its levels increase in the dorsaimost cells of the mesoderm. Be-... 

Figure 2. The function of tinman in the formation of mesodermal tissues. The (eft column shows wild-type embryos and the right column tinman mutant embryos of the same stage and stained with the same markers. (A, B) Neither cardioblasts nor pericardial cells are formed in tin mutants (embryos stained as in Figure 1 ). (C, D) The midgut musculature (stained for flCal expression from an enhancer trap insertion is completely m ssing in tinman mutants. (E, F Dorsal muscles (stained for [iCa expression from a .cZ reporter insertion Yin and Frasch, 1998) are not properly specified in tinman mutants. (G, H) Earlv stage 12. The muscle founders of the S59 cluster I (as detected with an S59 antibody), which give rise to muscles 5 and 25, are not specified in tinman mutants. By contrast, the founder cells of S59 cluster II are formed normally and will develop into muscles 26, 2(r, and 29, (I, J) Stage 11. huttonlesi niRN.A expression in the DM cell precursors (arrow) is absent in tin mutants and DM cells are not formed. (The bilateral pairs of nuclei are Eve-stained neuronal precursors).. Abbreviations DM dorsal median cell precursors dsm dorsal somatic muscles mgv m midgut visceral mesoderm pc pericardial precursors.

Yin and Frasch, 1998). Together with the zinc finger homeobox gene zfli-I, tinman is also required for normal formation of the gonadal mesoderm (Boyle et al., 1997 Broihier et al., 1998). It is likely that the functions of tinman in these developmental processes are required during its early phase of expression in the entire trunk mesoderm. 

Ectopic expression experiments have also been performed to study the functional potential of the tinman gene. Perhaps surprisingly, the consequences of prolonged ubiquitous tinman expression in the mesoderm or in the whole embryo were relatively mild. The main effect was a transient increase in the number of heart precursors during stage 11, but the formation of the heart, visceral muscles, and body wall muscles appeared not to be disturbed (Yin and Frasch, 1998). These results indicate that coregulators, whose expression or activity is spatially restricted, are obligatory for all known aspects of tinman function. 

Significant progress has been made in unraveling the genetic and molecular processes that control the development of the mesoderm in Drosophila. Three meso-dermally expressed genes, twist, tinman, and meJ2, have been found to play key... 

Gajewski, K., Kim, Y., Choi, C. Y, and Schulz, R. A. (1998). Combinatorial control of Drosophila mef2 gene expression in cardiac and somatic muscle cell linet es. Dev. Genes Evol. 208 382-392. Gajewski, K., Kim, Y., Lee, Y., Olson, E., and Schulz, R. (1997). D-mefi is a target for Tinman activation during Drosophila heart development. EMBO J. 16 515-522. 

---