University of California, Berkeley
Dept. of Integrative Biology
3060 VLSB #3140
Berkeley, CA 94720-3140
Lab TEL (510) 643-6227
FAX (510) 643-5022

Email: hannibal[at]berkeley.edu

Research Summary
 
In arthropods, annelids and chordates, the ectoderm and underlying mesoderm are organized into segments.  Although these phyla share the trait of segmentation, a current phylogenetic hypothesis places them into the three separate clades of the bilatarians.  As each of these clades also contains many unsegmented phyla, there is debate on whether segmentation in the arthropods, annelids and vertebrates is homologous.  To gain insight into whether segmentation evolved once or multiple times, segmentation must be studied in a diversity of segmented organisms and in both segmented tissue layers within these organisms.

In order to extend existing studies on the evolution of segmentation, I am examining mesoderm segmentation in the arthropod, Parhyale hawaiensis.  While studies of segmentation in “non-model” metazoans are increasing, many studies of arthropod segmentation focus only on the ectoderm.  When comparing mechanisms of segmentation between two organisms, homologous mechanisms could be overlooked if not all segmental layers are compared.  For example, a comparison between segmental mesoderm in one species and segmental ectoderm in another could miss similarities between the segmental mesoderm of both species.

Parhyale is an excellent model system in which to study segmentation because the presumptive mesoderm and ectoderm are separated very early in development.  At the eight-cell stage three large cells will form the ectoderm, while one large and two small cells will form the mesoderm.  Typically, one large cell, “Mav”, gives rise to head and visceral mesoderm, while two small cells, “ml” and “mr”, give rise to the left and right segmental mesoderm, respectively.  After gastrulation, the progeny of ml and mr will form eight Mesoteloblasts, the mesodermal stem cells.  The Mesoteloblasts will then migrate posteriorly in the embryo.  During this migration, the Mesoteloblasts will go through a series of asymmetrical divisions to produce the mesoblasts.  Each row of mesoblasts will become one segment’s worth of mesoderm.  This mode of segmentation contrasts with ectoderm segmentation, suggesting that the mesoderm and ectoderm may employ different mechanisms of segmentation. 

Currently, I am working on two questions.  My first research project addresses the question of whether mesoderm segmentation in Parhyale requires inductive signals from the ectoderm.  While mesoderm is the primary segmented tissue in vertebrates, various lines of evidence suggest that, in Drosophila, the most studied arthropod, the mesoderm receives segmental information from the ectoderm.  Since Drosophila is highly derived, we do not know whether this hold true for other arthropods.  Moreover, the developmental mode of Drosophila adds some uncertainty to the claim that the mesoderm receives all of its segmental information from the ectoderm.  Since segmental genes are transiently expressed in tissue that will become mesoderm later in development, there is debate to whether the mesoderm retains this information.  Parhyale is a great model system to investigate potential ectoderm-mesoderm interactions both because of its phylogenetic position and because of the ease at which the ectoderm and mesoderm can be manipulated separately from each other.  I am currently using ablation techniques to test the hypothesis that the mesoderm can segment independently of the ectoderm.  

My second research project addresses the question of whether gene cycling, which is critical for segmentation in some vertebrate systems, plays an important role in Parhyale mesoderm segmentation.  In many vertebrates, cycling of genes drives mesoderm segmentation.  One of these genes is the transcriptional repressor, snail.  Previous work in the lab has found that both Parhyale-snail1 (Ph-sna1) mRNA and protein cycle in the Mesoteloblasts.  Both are expressed during the migration of the Mesoteloblasts, but not before and during cell division, when they are stationary.  I am currently using missexpression and knock-down techniques to test the hypothesis that the cycling of Ph-Sna1 plays an important role in the migratory behavior of the Mesoteloblasts.

Education

Ph.D. Candidate
Advisor: Nipam Patel
Molecular & Cell Biology
University of California, Berkeley
2004 – Present

B.A. in the Biological Sciences
Honors in Biological Sciences
University of Chicago, Chicago, IL
2000 – 2004

Honors & Special Training
 
NSF-Spnsored International Graduate Training Course in Antarctic Biology
“Integrative Biology and Adaptation of Antarctic Marine Organisms”
McMurdo Station, Antarctica
January 4 – February 4 2006

Research Experience

Doctoral research with Dr. Nipam H. Patel
Department of Molecular & Cell Biology
“Mesoderm Segmentation in the Amphipod Crustacean, Parhyale hawaiensis”
University of California, Berkeley
2004 – Present

Undergraduate Research with Dr. Victoria Prince
“Retinoic acid regulation of Hox genes in zebrafish”
University of Chicago, Chicago, IL
2000 – 2004

Summer Intern with Dr. Greg Muller
“Affect of Nitrogen, a major air pollutant, on mushroom biodiversity”
Field Museum of Natural History, Chicago, IL
Summer 2003

Teaching Experience
 
Undergraduate Mentor
Patel Lab
University of California, Berkeley
Summer 2008 – Present

Teaching Assistant
Embryology (Arthropod Module)
Marine Biological Laboratory, Woods Hole, MA
Summers 2007 & 2008

Graduate Student Instructor
Developmental Biology (MCB131)
University of California, Berkeley
Spring 2007

Graduate Student Instructor
Cell & Developmental Biology Lab (MCB130L)
University of California, Berkeley
Fall 2005

Teaching Assistant
Developmental Biology Lab
University of Chicago
Spring 2003

Presentations

Speaker at the Society for Developmental Biology Annual Meeting
“The Role of Cyclical Ph-Snail1 Expression During Stem Cell Migration”
San Francisco, CA
July 2009

Speaker at the UC Berkeley Department of Molecular & Cell Biology Retreat
“Mesoderm Segmentation in the Amphipod Crustacean Parhyale hawaiensis”
UC Berkeley Department of Molecular and Cell Biology Retreat
Pacific Grove, CA
January 2009

Presented a Poster at the Integrating Evolution, Development and Genomics Conference
“The Interplay Between Mesodermal and Ectodermal Segmentation in the Amphipod Crustacean Parhyale hawaiensis”
Berkeley, CA
May 2008

Presented a Poster a the West Coast Society for Developmental Biology Regional Conference
“Potential Autonomous Segmentation of the Ectoderm and the Mesoderm in Parhyale hawaiensis”
Pacific Grove, CA
April 2007

Publications 

Rehm, E. J., Hannibal, R. L., Chaw, R. C., Vargas-Vila, M. A., and Patel, N. H.  (2009)  “The Crustacean Parhyale hawaiensis: A New Model for Arthropod Development” in Emerging Model Organisms: A Laboratory Manual, Volume 1.  (Crotty, D. A. and Gann, A. eds.), Cold Spring Harbor Laboratory Press.  New York.  pp. 373-404.