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A genetic and molecular analysis of the Drosophila dachs gene
The proximal-distal (P-D) axis is one of the three major body axes and is responsible for limb formation. Development in the Drosophila P-D axis is the least understood of the three axes due to historical and technical reasons. It arises the latest in sequence and requires some of the earlier genes expressed for anterior-posterior and dorsal-ventral axes development. Development in the P- D axis can be divided into two phases: initiation of the axis in imaginal discs in the larva, and growth and differentiation of the imaginal discs in larval through pupal stages into limbs. Initiation of the P-D axis in imaginal discs requires genes to establish the tissue identity, location along the developing embryo, and gross positional values of the imaginal discs. Absence of these genes results in loss of limbs. Growth and differentiation require genes to interpret the axis, i.e., to subdivide the axis molecularly, confer segment identity, carry out programs of proliferation/apoptosis, and finally execute distinct differentiation programs at different times. Loss of function of these genes results in loss of particular pattern elements. While genes for initiation have begun to be identified in both Drosophila and vertebrates, the latter class remains largely unknown. Furthermore, we still lack a clear paradigm for how this elaboration might take place. This study contributes to understanding P-D growth and differentiation by investigating the role of the dachs gene, whose mutant phenotype suggests a function in the axis. Based on the original dachs' mutation and eight new alleles examined in this thesis, the role of dachs seems to be to carry out growth and boundary formation in the intermediate P-D axis, which implies that it is not required for initiation, but rather for the mostly unknown process of interpreting the axis. dachs phenotypes include shortened femur, tibia, and tarsus, with a loss of one of the (normally five) tarsal joints, and a collapsed distance between the two crossveins in the wings. In the wings this collapsed distance is due to a loss of 50% of the cells in the inter-crossvein region. Thus, both growth and differentiation are affected. The molecular nature of dachs is unknown at present. This study uses genetic mapping to place its location in 29D1,2-D4,5 on the 2L chromosome, between the distal breakpoint of Df(2L)N22-5, a deficiency that uncovers dachs, and the acer gene. This chromosomal region contains approximately 83 kb of DNA, an interval which recently has been cloned and sequenced by the Berkeley Drosophila Genome Project. Initial RFLP analysis of y-ray-induced dachs alleles suggests that dachs may be on the proximal end of this interval. Finally, this study and other data from this laboratory implicate dachs in the same genetic pathway as four-jointed, a gene with very similar mutant phenotype. In addition, it is shown that dachs interacts with abelson (abl), a cytoplasmic tyrosine kinase and a homolog of a mammalian proto-oncogene, and possibly enabled, a proline-rich protein and substrate of abl, which is believed to transduce extracellular signals to the actin cytoskeleton.
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Includes bibliographical references (leaves 84-89).
Issued also on microfiche from Lange Micrographics.
Hu, Wei-Li (1999). A genetic and molecular analysis of the Drosophila dachs gene. Master's thesis, Texas A&M University. Available electronically from
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