TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL REGULATION OF MATERNAL AND ZYGOTIC CYTOSKELETAL TROPOMYOSIN MESSENGER-RNA DURING DROSOPHILA DEVELOPMENT CORRELATES WITH SPECIFIC MORPHOGENIC EVENTS

We have characterized maternal and zygotic cytoskeletal tropomyosin mR NA expression during Drosophila embryogenesis using in situ hybridizat ion to endogenous cytoskeletal tropomyosin mRNA and a cytoskeletal tro pomyosin promoter/beta-galactosidase-encoding fusion gene mRNA in tran sgenic flies. A 2.0-kb maternal cytoskeletal tropomyosin mRNA is synth esized in the nurse cells and transported into the oocyte during oogen esis. During early embryogenesis, this mRNA becomes localized to the p ole cell region and then to the cortex during the cellular blastoderm stage. In later embryos it is localized to the ventral and cephalic fu rrows and extending germ band. The major zygotic mRNA is 2.4 kb and is first detected at gastrulation. In early embryos, this mRNA is expres sed in the invaginating anterior and posterior midgut, the transverse furrows, and the amnioserosa, all regions of the embryo undergoing int ense cellular movement, and in later embryos, predominantly in the gut , brain, and epidermis. A transgene construct containing 1.2 kb of 5' cytoskeletal tropomyosin promoter sequences driving expression of Esch erichia coli beta-galactosidase and the cytoskeletal tropomyosin 3' un translated region in transgenic flies has the same distribution of mat ernal and zygotic transcripts throughout oogenesis and embryonic devel opment as the endogenous transcripts. A transgene containing the 3' un translated region from either the hsp70 gene or the SV40 early genes, on the other hand, does not express maternal RNA. Furthermore, none of the transgenes expressed in the follicle cells, suggesting that expre ssion in these cells is under different transcriptional control. Our r esults indicate that maternal and zygotic cytoskeletal tropomyosin mRN As are localized to specific regions of the developing embryo, particu larly in regions of the embryo undergoing cell movement and invaginati on. Furthermore, the synthesis, transport, and accumulation of this RN A is under transcriptional and post-transcriptional control. (C) 1994 Academic Press, Inc.