The Specification of Dorsal and Lateral Pattern in the Drosophila Embryo

Esguerra, Camila Vicencio (1994). The Specification of Dorsal and Lateral Pattern in the Drosophila Embryo. MPhil thesis The Open University.



The dorsal-ventral axis of the Drosophila embryo is established through the nuclear gradient expression of the maternal morphogen dorsal, which sets up the dorsal, lateral, and ventral domains along the embryo circumference. The steps from this maternal signal to the onset of patterning and morphogenesis is quite rapid, and although genetic approaches have identified several zygotic genes that are transcriptionally regulated by dorsal, the direct targets of these zygotic genes, as well as other targets of dorsal, are still unknown.

A molecular screen was utilized in order to identify genes that are differentially expressed along the dorsal-ventral axis, with a specific focus on dorsal-lateral genes involved in patterning and differentiation. A subtractive cDNA library highly enriched for genes expressed in the dorsal and lateral regions of the embryo was screened twice. From the two screens, 24 non-crosshybridizing clones were obtained, 21 of which appear to be novel genes based on preliminary sequence analysis and in situ hybridization patterns. Two clones turned out to be cDNA fragments of previously identified genes. One clone had an identical sequence to the Drosophila POU domain genes pdm-1 and pdm-2, while the other turned out to be tolloid, one of the dorsal-ventral patterning genes.

In conjunction with previously described genes, several clones from the library were then chosen to serve as molecular markers for specific domains along the dorsal-ventral axis. In situ hybridizations were performed on a series of mutant embryos either lacking progressively larger portions of the dorsal part of the embryo (zygotic ventralizing mutants), or lacking the entire mesoderm (twist snail double mutants). The aim of this thesis was to understand how patterning along the dorsal-ventral axis occurs, and to determine whether the current model on how the genes for the zygotic ventralizing mutants interact with one another to pattern the dorsal part of the embryo is correct. Indeed, a number of results show that this model may have to be revised.

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