Hox Genes

by Deutsch, Jean S., Ph.D.

• ISBN13: 9781441966728
• ISBN10: 1441966722
• Edition: 1st
• Format: Hardcover
• Copyright: 2010-06-25
• Publisher: Landes Bioscience

Summary

The purpose of this book is to argue, and to convince those who may not agree, that the Hox genes are indeed so important that their study will not end with the 20th century. The book is divided into three major sections. The first section covers aspects of the regulation of Hox gene expression and the structure and function of the now justifiably well-known homeobox. The second section offers insights and discussions of the sometimes contentious issues of the origin and evolution of the aforementioned Hox complexes. In the third and last section the role of the resident loci in the specification of body plans and meristic identity of thearthropods is presented.

Table of Contents

Mechanisms of Activity
Regulation of Hox Activity: Insights from Protein Motifs	p. 3
Abstract	p. 3
Introduction	p. 3
The Homeodomain	p. 4
The Hexapeptide Motif	p. 8
Additional Hox Functional Motifs	p. 9
Conclusion	p. 10
CIS-Regulation in the Drosophila Bithorax Complex	p. 17
Abstract	p. 17
Genetics of the Bithorax Complex: The Model of Ed Lewis	p. 17
The BX-C Encodes Only Three Genes, Ubx, abd-A and Abd-B	p. 19
The Segment-Specific Functions Act as Segment/Parasegment-Specific Enhancers	p. 22
Initiation and Maintenance Phase in BX-C Regulation	p. 23
Initiation, Maintenance and Cell Type-Specific Elements within the Cis-Regulatory Domain	p. 25
The Cis-Regulatory Regions Are Organized in Segment-Specific Chromosomal Domains	p. 26
Chromatin Boundaries Flank the Parasegment-Specific Domains	p. 28
Elements Mediating Long-Distance Cis- and Trans- Regulatory Interactions	p. 28
Transvection Studies	p. 28
Promoter Targeting Sequences	p. 31
Promoter Tethering Element	p. 32
Intergenic Transcription in the BX-C	p. 32
MicroRNAs in the BX-C	p. 34
Conclusion	p. 35
Maintenance of Hox Gene Expression Patterns	p. 41
Abstract	p. 41
Introduction	p. 41
Genetics of PcG and trxG Genes	p. 42
PcG Proteins and Their Complexes	p. 43
TrxG Proteins and Their Complexes	p. 46
ETP Proteins	p. 46
PcG and trxG Response Elements	p. 47
Recruitment of Maintenance Proteins to Maintenance Elements	p. 48
Role of Maintenance Proteins in Regulation of Transcription	p. 50
Epigenetic Marks	p. 51
Release of PcG Silencing	p. 53
Role of PcG Proteins in Chromatin Replication	p. 54
Role of PcG Proteins in Stem Cells	p. 54
Conclusion	p. 55
Future Research in the Field	p. 55
Control of Vertebrate Hox Clusters by Remote and Global Cis-Acting Regulatory Sequences	p. 63
Abstract	p. 63
Introduction	p. 63
Colinearity and Clustering of the Homeotic Genes: An Obligatory Functional Link?	p. 64
Vertebrate Hox Clusters Are More Clustered Than Others	p. 65
Global Regulation of the Complex through Shared Mechanisms: The Retinoic Acid Connection	p. 66
High-Order Structures Over the Complex and Colinearity	p. 66
Control of Vertebrate Hox Genes by Shared Internal Enhancers	p. 67
The Ins and Outs of Hoxd Gene Regulation	p. 67
The Role of the Flanking Regions in the Control of Vertebrate Hox Genes	p. 68
Control of the HoxD Cluster through Remote Enhancers	p. 69
Regulation of the HoxD Cluster and More: Global Control Regions and Regulatory Landscapes	p. 70
Remote Enhancers for the Other Vertebrate Hox Clusters?	p. 71
An Evolutionary Success Story and an Increasing Need for a Global Regulation	p. 73
Conclusion and Outlook for Hox Gene Regulation in the 21st Century	p. 74
Evolution of Hox Genes and Complexes
The Early Evolution of Hox Genes: A Battle of Belief?	p. 81
Abstract	p. 81
The Hox System	p. 81
Phylogenetic Evidence	p. 82
Opposing Views	p. 84
Conclusion	p. 87
Evolution of Hox Complexes	p. 91
Abstract	p. 91
Introduction	p. 91
Origin of the ProtoHox Gene	p. 91
Origin of the Hox Cluster from a ProtoHox Cluster, or Not?	p. 92
Expansion and Contraction of the Number of Hox Genes in Evolution	p. 96
Conclusion	p. 98
The Nematode Story: Hox Gene Loss and Rapid Evolution	p. 101
Abstract	p. 101
Introduction: Hox Gene Loss, the Third Way	p. 101
The Caenorhabditis elegans Hox Cluster, an Extreme Case of Gene Loss	p. 102
Tracing Hox Gene Loss through the Nematode Phylum: Mode and Tempo	p. 104
Sea Squirts and Nematodes: Why Do Both Groups Lose Hox Genes	p. 105
Hox Gene Loss in Flagrante	p. 106
Nematode Hox Gene Function: A Story of Novelty, Conservation and Redeployment	p. 106
Conclusion	p. 108
Are the Deuterostome Posterior Hox Genes A Fast-Evolving Class?	p. 111
Abstract	p. 111
The Distribution of the Posterior Hox Genes in the Metazoa	p. 111
Early Duplications of the Posterior Hox Genes	p. 113
The 'Deuterostome Posterior Flexibility' Hypothesis	p. 114
The Mechanistic Basis of Deuterostome Posterior Flexibility	p. 116
Conclusion and Future Directions	p. 118
Biological Function
Hox Genes and the Body Plans of Chelicerates and Pycnogonids	p. 125
Abstract	p. 125
Arthropods, Mandibulates vs Chelicerates	p. 125
Chelicerate Hox Genes	p. 126
Chelicerate Hox Genes and the Chelicerate vs Mandibulate Body Plan	p. 127
Hox Genes and the Enigmatic Sea Spider Body Plan	p. 130
Conclusion	p. 131
Hox3/-zen and the Evolution of Extraembryonic Epithelia in Insects	p. 133
Abstract	p. 133
Introduction	p. 133
Setting the Stage: Morphological Evolution of Extraembryonic Development	p. 134
Variants of zen Expression and Function in Insects and Possible Morphological Correlates	p. 135
The Amnioserosa Gene-Network in Evolutionary Perspective	p. 140
Conclusion	p. 141
Hox Genes and Brain Development in Drosophila	p. 145
Abstract	p. 145
Introduction	p. 145
Expression and Function of Hox Genes in Embryonic Brain Development	p. 146
Genetic Interactions between Hox Genes in Embryonic Brain Development	p. 148
Hox Genes in Postembryonic Brain Development	p. 149
Evolutionary Conservation of Hox Gene Action in Brain Development	p. 151
Conclusion	p. 152
Homeosis and Beyond. What is the Function of the Hox Genes?	p. 155
Abstract	p. 155
What Are the Hox Genes?	p. 155
The Hox Genes' Explosion	p. 156
What Is the Function of a Gene?	p. 156
Hox Genes' Function at the Molecular and Cellular Levels	p. 157
Hox Genes and Homeosis	p. 157
Homeosis as a Differential Function	p. 157
Hox Genes as 'Meta-Selector' Genes	p. 158
The Hox Specificity Paradox	p. 158
Posterior Prevalence	p. 159
An Evolutionary Paradox: Morphological Differentiation and the Hox Repertoire	p. 159
Hox and Neuronal Homeosis	p. 159
Morphological Homeosis as a Derived Property	p. 160
Why Does the 'Hox System' Make Sense?	p. 160
Conclusion	p. 161
Index	p. 167
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