Lamprey Krox Reveals Ancient Origin of Vertebrate Hindbrain Segmentation
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Authors
Neef, Haley C.
Issue Date
2002
Type
Thesis
Language
en_US
Keywords
Alternative Title
Abstract
The taxon Vertebrata is made up of non-jawed vertebrates and jawed vertebrates,
or gnathostomes. Molecular and morphological characteristics distinguish vertebrates
from other chordates and also help define phylogenetic relationships among lampreys,
the only extant non-jawed vertebrates, and gnathostomes. Studying genes that dictate
vertebrate head structure and organization is of particular interest because the
specialization of head structures early in development gives rise to many characteristic
vertebrate adult morphologies. Additionally, to gain insight into early vertebrate
evolution, it is important to understand when duplications of genes that control head
structure occur, at the vertebrate origin or at the lamprey-gnathostome divergence.
Krox-20, a gene that helps form and maintain hindbrain segmentation in gnathostomes,
is expressed in the third and fifth hindbrain segments during embryonic development
and contributes to segmental specialization in later development. A paralog, Krox-24,
also exists in gnathostomes. In this study, we have cloned, phylogenetically analyzed,
and shown the developmental expression of a lamprey Krox homolog in Petromyzon
marinus. Our results suggest that hindbrain segmentation is present in lampreys and
therefore is characteristic of all vertebrates, and also that lamprey Krox is an ortholog of
gnathostome Krox-20. This orthology gives preliminary evidence that the Krox gene
duplication event occurred prior to the vertebrate origin.
Description
v, 29 p.
Citation
Publisher
Kalamazoo College
License
U.S. copyright laws protect this material. Commercial use or distribution of this material is not permitted without prior written permission of the copyright holder.