Research Interests:

Much of the molecular understanding of arthropod limb development comes from studies on the leg imaginal disc of Drosophila melanogaster. The fly limb is a relatively simple unbranched (uniramous) structure extending out from the body wall. The molecular basis for this outgrowth involves the intersection of two signaling pathways, dpp and wg, to create a single domain of distal outgrowth, clearly depicted by the expression of the Distal-less gene (Dll). The uniramous limb form has been studied in good detail; expression of wg and dpp during the development of other arthropod thoracic limbs indicates that the use of these pathways might be conserved across arthropods for uniramous limb development. The appendages of crustaceans and the gnathal appendages of insects, however, exhibit a diverse array of morphologies, some with no distal elements, such as the mandible, and others that are branched or possess multiple lobes as seen in many crustacean limbs and the maxilla and labium of insects. I am interested in two questions; first, why does the mandible lack any distal element or Distal-less expression and second, how are branched appendages made. It is unclear how, if at all, the known patterning genes for making a uniramous limb might be deployed to generate these diverse appendage forms. To do this I have been analyzing the expression of wg, dpp, and Dll in the development of these gnathal appendages of the grasshopper, Schistocerca americana, and the flour beetle, Tribolium castaneum.

The gnathal appendages of beetles and grasshoppers are well suited to understand how non-uniramous limb forms develop. First, the gnathal appendages of beetles and grasshoppers are of the more “typical” mandibulate form. The mandible, though gnathobasic, is a distinct element unlike the Drosophila mandible, which is largely non-existent. The maxilla and labium have a leg-like palp and may possess ventral branches, whereas the Drosophila maxilla is extremely reduced and the labium is a highly derived sponging device. Hence, the adult fly mouthparts, though interesting, do not represent good cases for studying typical gnathobasic and branched appendages. Second, the beetle and grasshopper limbs and gnathal appendages all form directly out from the body wall allowing us to easily visualize their entire development as well as directly compare development between them. Understanding this relationship in flies is complicated due to the highly derived nature of the imaginal discs, such that there is no great understanding of the whole development, from embryo to adult, of any of the appendages. And though the legs are relatively well understood, the gnathal appendages of Drosophila are particularly confusing because the embryonic cells of the gnathal segments contribute to both the highly derived larval mouthparts and the imaginal discs.

In addition to understanding the non-uniramous limbs of insects I am also interested in understanding how diverse crustacean limbs are patterned by the wg+dpp system. To this end I am cloning and visualizing the expression patterns of wg, dpp, and Dll in the amphipod, Parhyale hawaiensis.

[PDF] Dissertation

Publications and Abstracts

Giorgianni, M.W. and Patel, N.H. (2004). Patterning of the gnathal appendages in Schistocerca americana and Tribolium castaneum by wingless, decapentaplegic and Distal-less. (Poster to be presented at The Drosophila Research Conference (March 21st-28th)

Giorgianni, M.W. and Patel N.H. (2003). Complex appendage development in arthropods. (Poster presented at The Developmental Basis of Evolutionary Change III, October 16th-19th)

Giorgianni, M.W., Gleich, N.R., DiPietro, D., Averof, M., Patel, N.H. (2000). Evolution of arthropod appendage development. 59th Annual SDB Meeting.

Moens, C.B., Cordes, S.P., Giorgianni, M.W., Barsh, G.S., Kimmel, C.B. (1998). Equivalence in the genetic control of hindbrain segmentation in fish and mouse. Development 125: 381-391.

Lynch, M., Latta, L., Hicks, J., Giorgianni, M. (1998). Mutation, selection, and the maintenance of life-history variation in a natural population. Evolution 52: 727-733.

Meetings Attended

The Developmental Basis of Evolutionary Change III (Chicago, IL) 10/03
Meeting at the Howard Hughes Medical Institute (Chevy Chase, MD) 10/03
Drosophila Research Conference (Chicago, IL) 3/03
The Developmental Basis of Evolutionary Change II (Chicago, IL) 10/01
Drosophila Research Conference (Washington, DC) 3/01
59th annual SDB Meeting (Boulder, CO) 6/00
Drosophila Research Conference (Pittsburgh, PA) 3/00
58th Annual SDB Meeting (Charleston, VA) 6/99
The Developmental Basis of Evolutionary Change I (Chicago, IL) 5/99

Meetings Organized

The Developmental Basis of Evolutionary Change II (Chicago, IL) 10/01

Education:

Ph.D
University of Chicago
Committee on Developmental Biology
Advisor: Nipam H. Patel
1998-2004

B.S. Biology
University of Oregon
1992-1996