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L. Patricia
Hernandez
Assistant Professor of Biology
Evolutionary Developmental
Biology of Vertebrates
Department of Biological Sciences
The George Washington University
Lisner Hall 340, 2023 G Street, NW
Washington, D.C. 20052
Lab: (202) 994-4574
Office: (202) 994-6930
Fax: (202) 994-6100
E-Mail: phernand@gwu.edu
Dept E-mail : biology@gwu.edu
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Education:
B.S. in Biology, Eckerd College
Ph.D. in Biology, Harvard University
Research Interests:
Craniofacial development using the zebrafish model system:
Research in my lab centers around uncovering the developmental mechanisms
involved in vertebrate head formation. I primarily use the zebrafish
model system to examine the mechanisms involved in the morphogenesis
of the pharyngeal arches and neurocranium. The vertebrate skull
is composed of 3 basic units: the chondrocranium/neurocranium encases
and protects the brain; the dermatocranium (composed of dermal bone)
covers the neurocranium and makes up a significant portion of the
cranial vault; and the viscerocranium, derived from seven pharyngeal
arches, gives rise to the jaws and gill bearing structures in fishes.
In mammals the viscerocranium consists of the jaws and associated
structures, which support the throat and laryngeal structures. The
pharyngeal arches in zebrafish embryos represent a series of relatively
simple reiterated structures whose development depends on all three
germ layers as well as neural crest cells. The relative simplicity
of these embryonic structures affords an ideal situation in which
to study the molecular mechanisms involved in the interactions among
germ layers in these structures.
Presently I am investigating the role of the Hedgehog pathway in
the proper growth and differentiation of the cartilaginous components
of the pharyngeal arches. Using mutant analysis, overexpression,
and pharmacological treatment with cyclopamine my lab is investigating
the role Hedgehog proteins play in the differentiation of the branchial
cartilages (which support the gills). Our previous findings suggest
that the Hh signaling pathway is required for growth of the jaws,
hyoid and branchial cartilages, and more importantly it is required
for the differentiation of branchial cartilages. Work on this project
is ongoing.
Evolutionary developmental biology of fishes:
For many years I have been interested in the comparative cranial
anatomy of fishes. It is clear that the skulls of fishes are much
more complex than mammalian skulls, showing an enormous amount of
structural diversity. Jaws and associated cranial structures differ
from the small picking jaws of the butterflyfishes to the large
straining branchial arches of the paddlefish. Such structural complexity
coupled with amazing morphological diversity makes this group especially
well suited for study within an evolutionary developmental perspective.
How has this enormous morphological diversity evolved? Ultimately
natural selection acts to cull failed experiments, but the only
way that novel morphologies are generated is through modification
of developmental mechanisms.
Thus a second area of study within my lab entails investigating
the developmental mechanisms (as defined through molecular interactions/mechanisms)
that are involved in the generation of different morphologies. While
differential growth between ancestors and descendents (i.e. heterochrony)
has been invoked to explain morphological differences among species,
the molecular mechanisms involved in such shape/size changes have
been poorly resolved. While heterochrony assuredly plays a key role
in many of these morphological changes, to fully understand how
these changes have evolved we must understand precisely which molecular/genetic
mechanisms brought about changes in growth trajectories. Previous
work using the comparative method has done much to establish the
morphological patterns we see during the course of evolution, yet
in order to specifically identify the factors responsible for morphological
change we need to isolate the genetic factors involved.
Thus, in addition to our work on the development of the visceral
arches in zebrafish, we are also examining the development and evolution
of the neurocranium in zebrafish and a number of congeners. Previous
work has shown that defects in the Hedgehog signaling pathway lead
to defects associated with growth within the anterior neurocranium.
This would suggest that during normal development, the Hh pathway
plays an important role in the proper morphogenesis and growth of
the anterior neurocranium. By conducting a morphometric analysis
of shape changes in the neurocranium in a number of related cyprinids
we hope to generate hypotheses concerning the role of Hh in neurocranial
development within this group.
During the course of my postdoctoral work I became interested in
the development and evolution of muscle fiber type proportion and
distribution in cranial muscles. While an enormous amount of research
effort has been placed on examining extensive differences in musculoskeletal
architecture in the head, it is clear that relatively minor differences
in fiber type composition and distribution may have a disproportionately
large impact on animal performance. Moreover the genetic factors
involved in fiber type specification are being uncovered. To this
end my lab is investigating the evolution and development of muscle
fiber type changes within cranial muscles. My previous work on zebrafish
has shown that ontogenetic changes in cranial muscle fiber type
proportion are correlated with changes in feeding mode. If this
is true among ontogenetic stages, it is likely also true among different
species of closely related fishes. Thus, we are presently analyzing
fiber type distribution in a number of related Danios.
Finally my doctoral student, Nathan Bird, and I are examining the
development and evolution of the Weberian apparatus, a novel bony
connection between the inner ear and swim bladder, which characterizes
the Otophysi. We believe that this probable key innovation has led
to a major radiation (~27% of all fish species) within this group.
We are mapping a number of gene expression patterns, as well as
larval and adult morphological characters unto a known phylogeny
to better understand how this complex structure has developed and
evolved.
RECENT
PUBLICATIONS
Hernandez, L. P., M. J. F. Barresi and S. H. Devoto. 2002. Functional
morphology and developmental biology of zebrafish: reciprocal illumination
from an unlikely couple. Integrative and Comparative Biology, Volume
42(2): 222-231.
Barresi M.J.F., D'Angelo J.A., Hernandez L.P., and Devoto S. H.
2001. Distinct mechanisms regulate slow-muscle development. Curr.
Biol. 11 (18): 1432-1438.
Hernandez, L. P. 2000. Intraspecific scaling of feeding mechanics
in an ontogenetic series of zebrafish, Danio rerio. J. Exp. Biol.
203: 3033-3043.
Hernandez, L. P. and P. J. Motta. 1997. Trophic consequences of
differential performance: ontogeny of oral jaw crushing performance
in the sheepshead, Archosargus probatocephalus (Teleostei: Sparidae):
J. Zool. 243:737-756.
Courses:
Undergraduate:
Bisc
132 - Comparative Vertebrate Anatomy, Spring
BiSc
168 - Tropical Marine Biology, Fall and Summer
Graduate:
BiSc 249
-Topics in Developmental Biology, Fall
WWW Links of Interest:
Society for Integrative and Comparative Biology
Society for Developmental Biology
International Society for Vertebrate Morphology
ZFIN
American Society of Ichthyologists and Herpetologists
Museum of Comparative Zoology
National Museum of Natural History
National Institutes of Health
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