Abstract of Thesis

The paucity of developmental, genetic, and evolutionary data available in non-model systems leaves critical questions regarding the tempo and mode of evolution in generating extant biological diversity unanswered. These questions can begin to be addressed by 'gap-filling' with new systems more closely related to systems currently in use. The insect and crustacean lineages are thought to be closely allied. Crustaceans are an enormously successful group, possessing a wide diversity of morphologies and life histories. My dissertation focuses on developing a crustacean 'model system' to fill a critical taxonomic gap for the functional study of embryogenesis.

I identified a crustacean species, Parhyale hawaiensis, suitable for laboratory culturing and embryonic analysis. Parhyale embryos are robust and resistant to environmental variations and thus are suitable for experimental manipulation. Parhyale embryos develop directly and hatchlings are morphologically similar to adults. I completed a etailed descriptive analysis of Parhyale embryogenesis, compiling data from in vivo description, nuclear DNA distribution, and two commonly used panspecific antibodies as molecular markers during segmentation and limb formation. Complete embryogenesis requires ~250hrs at 26 degrees Celcius. I divided embroygenesis into 30 stages. Significant to further studies, the early cleavage program is total and holoblastic and generates an eight-cell embryo. The staging data generated for Parhyale will facilitate comparative analysis of embryonic development among Crustacea as well as divergent arthropod groups such as Insecta, Myriapoda and Chelicerata.

The eight-cell stage of Parhyale is amenable to microinjection techniques. Lineage tracing experiments identified specific and invariant lineages that map uniquely to these eight blastomeres. The early establishment of distinct cell lineages will facilitate experimental manipulations of cell lineage and germ layers via microinjection and other pertubation techniques.

To explore the mechanism of 'pair-rule' patterning in segmentation, I cloned the Parhyale homolog of Drosophila hairy. In situ hybridization suggests a requirement for Ph hes in every segment. This is inconsistent with the two-segment periodicity patterning role of hairy in Drosophila. The Parhyale expression data suggests that 'pair-rule' patterning mechanisms may be restricted to the insect lineage. To assess the validity of this hypothesis requires analysis of hairy expression and other 'primary pair-rule' genes in additional arthropods.

Areas of interest:

Hox gene expression, regulation, and function in various arthropods. Collection of specimen and analysis of evolutionary process and history.

Education:

1994 - 2003

Ph.D., University of Chicago, Molecular Genetics and Cell Biology. Funded under National Institute of Health Fellowships (Biotechnology Training Grant, and Molecular Cell Biology Training Grant) and the H.F.S.P.O.. Student Representative (95-96) and student member of Graduate Minority Committee (96-).

1994

University of Chicago,
B.A. in the Biological Sciences

Research Experience:

1999

Field collection of crustacean embryos at Smithsonian Institution Marine Station located in Fort Pierce, Florida. Habitats sampled included jetties, floating piers, intercostal mud flats, sand flats, and offshore plankton tows in the Gulf Stream. This study was funded by Howard Hughes Medical Institute and carried out in conjunction with Frank Ferrari, curator, Smithsonian Institution.

Member of three person organizing committee for symposium entitled, The Developmental Basis of Evolutionary Change. Project involved all aspects of planning and coordinating a multiday symposium which featured speakers recognized as leaders in the fields of developmental biology, evolutionary biology, and paleontology. The symposium successfully attracted a diverse international audience of several hundred. Funding was secured principally through a grant from NASA life sciences division as well as significant support from University of Chicago and several biotechnology firms. (http://evodevo.bsd.uchicago.edu)

1996

University of Chicago, researcher with the Patel lab. Thesis project involves the study of Hox gene expression, regulation, and function in various arthropods. Endogenous gene expression domains will be defined and results will be used to interpret important evolutionary gene regulation changes. Experiments using viral expression systems will extend and reduce the endogenous expression domains and results will be used to interpret aspects of cell fate determination mediated by Hox gene function.

1995-96

University of Chicago, researcher with the Preuss lab. Project focus included; 1) design of experiments, methodologies, and techniques required for measurement of rates of genetic recombination to establish the chromosomal location of functional centromeres in Arabadopsis, 2) design of screens and techniques for identification of genes important for male gametophytic development in Arabadopsis.

1995

Abbott Laboratories, research intern in the Diagnostics Division. Worked with the Probe Development Group. Project focus was to identify and test variables affecting the performance of DNA chips. The primary goal was to utilize experimental design to identify important parameters for increasing the intensity of light signals emanating from the DNA chip surface.

1994

Member of icthyological expedition to Amazonas, Venezuela. During the three week expedition, eight scientists from various disciplines lived in a hollowed out log canoe while moving among remote rain forest sites collecting fish (principally Apterontidae and Gymnotidae) for both phylogenetic study and information concerning cranial nerve innervation. Study was sponsored by University of Michigan, FUDECI, and Universidad Central de Venezuela.

1994

Sigma Xi Scientific Society

1993

Member of ichthyological expedition to southern Illinois. Primary objective was the live capture of gar and bowfin fish which were used to collect data concerning unique muscle contractile properties during the execution of escape responses and C-starts. Data was collected through the combined use of high speed video, electrode implants, and pressure transducer implants.

1993-94

University of Chicago, student researcher with the Rothman-Denes lab. Independent project utilized molecular genetic and biochemical techniques to study the structural and functional relationships between N4 RNA polymerase II and promoters of middle transcription in the bacteriophage N4.

1990-94

Field museum of Natural History, student researcher with the Division of Fishes. Prince Fellow (1991-1993). Responsibilities included identifying recently collected specimens and extensive chemical preparation for both the storage, and clearing and staining of specimens for use in further research. Collected meristic data for use in establishing systematic relationships between related taxa. Analyzed high speed video to generate data for examining bio-mechanics of fish locomotion. Experience in scanning electron microscopy and data base management.

Publications and presentations:

2002

Gerberding, M., Browne, W.E., and N. H. Patel (2002) Cell lineage analysis of the amphipod crustacean Parhyale hawaiensis reveals an early restriction of cell fates. Development 129:5789-5801.

2000

Browne, W.E., and Patel, N.H. Molecular genetics of crustacean feeding appendage development and diversification. Semin Cell Dev Biol 11, 427.

1999

Browne, W., Davis, G. and McClintock, J. , "Ancestors and variants: tales from the cryptic, Evol. & Dev. 2(3), 130. (Review of meeting, The Developmental Basis of Evolutionary Change, University of Chicago, May 13 - 15.

1999

Poster, The Developmental Basis of Evolutionary Change, "Functional and evolutionary implications of changing Hox gene expression boundaries".

1998

Copenhaver, G.P., Browne, W.E., and Preuss, D. Assaying genome-wide recombination and centromere functions with Arabidopsis tetrads. Proc. Natl. Acad. Sci., USA, 95, 247-252.

1997

Spielman, M., Preuss, D., Li, F-L., Browne, W.E., and Scott, R.J. TETRASPORE is required for male meiotic cytokinesis in Arabidopsis thaliana. Development 124, 2645-2657.

1997

Poster, Departmental Retreat, "Functional and Evolutionary Implications of Changing Hox gene expression boundaries".

1996

Poster, Midwest Development Meeting, "Using the Arabidopsis QUARTET mutant: Tetrad Analysis and Haploid-Specific Mutations".

1995

Poster, Departmental Retreat, "Using the Arabidopsis QUARTET mutant : Tetrad Analysis and Haploid-Specific Mutations".

Research Interests:

I am driven by the immense range of biological diversity and the relationship between phenotype and genotype. The correlation between genotypic and phenotypic variation is most beguiling. How is observed organismal diversity generated? What are the rules governing this connection between genotype and phenotype? And importantly, how are these rules interpreted by organisms passaging through evolutionary time? Further resolution of some of these major questions of both evolutionary process and history require a multidisciplinary experimental approach.

My thesis research focuses on Hox gene expression, regulation, and function. Hox genes are members of the homeodomain family of transcription factors which regulate body plan development in a number of metazoan phyla. This process appears to be driven through regulation of specific cell fate and determination events. I have set out to test some proposed evolutionary aspects of Hox gene expression and correlated changes in cell fate and morphology in arthropods.

Arthropods have a great diversity of body plans which are reflected in differential segment fates and thus are particularly well suited for comparative Hox gene expression analysis. Within arthropods it is crustaceans that demonstrate the greatest degrees of morphological divergence and differential segmental fates. These variable segment fates have been hypothesized to be under the control of Hox gene complex members. Previous comparative studies of Hox gene expression domains suggest that both radical and subtle changes in gene expression boundaries have correlated with changes in both body plans and segmental fates through evolutionary time. These observations raise an important question concerning diversity of metazoan body plans. Have changes in regulation of Hox gene expression played an important role in evolution of morphology? From early data it is clear that future studies must be extended to include both a wider range of related organisms and a wider range of Hox gene complex members. This is crucial in assessing the relative evolutionary importance of regulatory changes in Hox gene expression domains during embryonic development.

Cloned Hox gene sequences are used for generating in situ probes which delineate endogenous gene transcript expression domains during embryogenesis. Cloned sequences are used to probe embryonic cDNA libraries for full length transcripts. These cDNAs will then be used for two purposes. One, insertion into misexpression vectors followed by injection into developing crustacean embryos. Resulting phenotypes will be examined and should provide support for the evolutionary inferences drawn from comparative analysis of endogenous expression domains. Perturbation experiments are predicted to produce changes in specific cell fates and thus shed light on morphogenetic transitions of segmental fates. Some of these morphogenetic transitions will be predicted based upon previous genetic studies in Drosophila involving both ectopic and mutant expression of Hox genes. However, by virtue of greater morphological divergence within crustaceans, novel fate transitions associated with novel expression domains may serve to illuminate additional Hox gene functions in cell fate decisions and segmental identity determination.