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«Joshua Frederick Coulcher UCL Submitted for the Degree of Doctor of Philosophy September 2011 Declaration I, Joshua Frederick Coulcher, confirm that ...»

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Evolution of the Arthropod Mandible:

a molecular developmental perspective

Joshua Frederick Coulcher

UCL

Submitted for the Degree of Doctor of Philosophy

September 2011

Declaration

I, Joshua Frederick Coulcher, confirm that the work presented in this thesis is

my own. Where information has been derived from other sources, I confirm that this

has been indicated in the thesis.

Abstract

The mandible is thought to have evolved once in the ancestor to the mandibulate arthropods; the insects, crustaceans and myriapods. If the mandible is a homologous structure, it suggests that there will be shared developmental genes required to pattern the mandible in different species. As a representative of mandibulate arthropods, the red flour beetle Tribolium castanem was chosen to study genes required to pattern the mandible. This study show that the Tribolium orthologue of cap’n’collar (Tc cnc) patterns the mandible of Tribolium. Loss of Tc cnc function by RNA interference (RNAi) results in a transformation of the mandible to maxillary identity and deletion of the labrum. Analysis of gene expression by in situ hybridisation shows that Tc cnc represses the Tribolium orthologues of the Hox genes proboscipedia (pb) and Deformed (Dfd), which pattern the maxillary appendage.

Similar expression patterns of cnc, Dfd and pb homologues in mandibulate arthropods suggests that the functions of these genes are conserved. As the mandible has evolved from a maxilla-like precursor in the ancestor to all mandibulate arthropods, the manner in which Tc cnc differentiates the mandible from a maxilla in Tribolium recapitulates the evolution of the mandible from a maxilla-like precursor.

An orthologue of cnc was cloned from the spider Achaearanaea tepidariorum, chosen as an outgroup to the mandibulate arthropods, but no evidence of a developmental role was discovered.

Study of the expression of genetic markers for appendage segments shows that the biting edge of the mandible is derived from one endite, and the mandible is divided into a subcoxa and coxa which are also present in the maxillary, labial and leg appendages. There are significant similarities in the expression of genetic markers that presumably indicate serial homology of the subcoxa and coxa of the mandible to the subcoxa and coxa of other appendages.

Acknowledgements I would to thank my supervisor Max Telford for all the valuable help and guidance he has given me over the past few years. I would also like to thank Paola Oliveri for all her support she has given me during my PhD.

I would like to thank several co-workers, both past and present, in the laboratory that I have been working in over the last four years. I am grateful to Bernhard Egger, Kate Rawlinson, Fraser Simpson, Omar Rota-Stabelli, Andrew Economou, Rob Lanfear for many interesting and lively discussions as well as helping me in the laboratory with my experiments. I would also like to thank Giovanna Vinti for all the help that she has given me during my time at UCL.

Many thanks go to Nico Posnien, Andrew Peel and Meriem Takarli for both giving me invaluable advice and demonstrating experimental techniques in Tribolium.

Many thanks also go to Nikola-Michael Prpic-Schäper, Alistair Mcgregor, Matthias Pechmann and Viktoria Linne for helping me learn how to maintain a healthy spider culture and also for all their advice on performing experiments on Achaearanea.

I would also like to thank Gregor Bucher, Angelika Stollewerk, Michalis Averof and Linda Partridge for kindly inviting me into their laboratory in order to learn experimental techniques and also for allowing me to use their facilities.

I am indebted to the Biotechnology and Biological Sciences Research Council (BBSRC) for providing the financial support necessary for me to perform the research which is presented in this thesis.

I would like to thank my father, for without his support and encouragement this thesis would never have been possible. Finally, I would like to thank my partner Cécile for being supportive, helping out with my experiments and not least for putting up with my anti-social hermit-like existence for the substantial period of time it took to write this thesis.

Table of Contents

Abstract

Acknowledgments

Table of contents

List of figures

List of tables

Chapter 1: Introduction

1.1 General introduction

1.2 Evolution of the biramous limb

1.3 Mandible diversity

1.4 Arthropod Phylogeny

1.5 Arthropod Fossil Record in the Cambrian

1.6 Serial homology of the mandible and maxilla

1.7 Molecular development of the mandible

1.8 Homology of anterior arthropod segments

1.9 Mandibular segment patterning genes in Drosophila.

1.10 The red flour beetle Tribolium castaneum

1.11 Introduction to results chapters

Chapter 2: Development of the embryonic mandibular endite in Tribolium............. 65 2.1: Introduction

2.2: Results

2.3: Discussion

Chapter 3: Division of the Tribolium embryonic mandible into a subcoxa and coxa. 80 3.1: Introduction

3.2: Results

3.3: Discussion





Chapter 4: Tc cnc differentiates the mandible from a maxilla in Tribolium............ 110 4.1: Introduction

4.2: Results

4.3: Discussion

Chapter 5: The protopodite patterning role of Tc Dfd in the maxilla.

5.1: Introduction

5.2: Results

5.3: Discussion

Chapter 6: Investigating the role of mandible patterning genes in non-mandibulate arthropods

6.1: Introduction

6.2: Results

6.3: Discussion

Chapter 7: Discussion

7.1: General overview of results

7.2: The mandibular subcoxa

7.3: Molecular development of the mandible

7.4: The role of cnc in the ancestor to all mandibulates

7.5: General Conclusions

Chapter 8: Materials and Methods

8.1: Animal culture

8.2: Molecular biology techniques.

8.3: in situ hybridization protocols.

8.4: Microscopy

8.5: Parental RNAi in Tribolium

References:

Appendix 1: Solutions and Media

Appendix 2: Primer sequences

Appendix 3: Details of Tc cncRNAi experiments

Appendix 4: Details of Tc DfdRNAi experiments

Appendix 5: Details of additional RNAi experiments

Appendix 6: CNC and bZIP family members

Appendix 7: Sequence of the homologue of cap’n’collar in Achaearanea.............. 251

–  –  –

Fig.1.5. Two competing Arthropod phylogenetic relationships, the Mandibulata and Myriochelata hypotheses..................................................30 Fig.1.6. The crustaceamorph Martinssonia elongata, a possible stem lineage representative of Mandibulata............................................. 34 Fig.1.7. Hypothetical mandible evolution from an ancestral biramous limb.........38 Fig.1.8. Hypothetical maxilla evolution from an ancestral biramous limb........... 41

–  –  –

Fig.1.12. Comparison of mandibulate (represented by Tribolium) and Drosophila larval and embryonic morphology................................................57 Fig.2.1. Hypothesis of the serial homology of the mandibular inner and outer lobes to the maxillary lacinia and galea endites after Machida (2000)..................... 68 Fig.2.2. Scanning electron micrographs (SEMs) of developing gnathal appendages of Tribolium embryos showing the inner and outer lobes......................... 70 Fig.2.3. Development of the mandible and maxillary endites in the gnathal appendages of Tribolium embryos as revealed by expression of Tc Dll and Tc prd...............71

–  –  –

Fig.3.1 Hypotheses of serial homology of the putative mandibular subcoxa to the cardo of the maxilla and the subcoxa of the leg......................................81 Fig.3.2. Scanning electron micrographs (SEMs) of developing gnathal appendages of Tribolium embryos showing the presence of a subcoxa/coxa boundary on the developing mandible...................................................... 86 Fig.3.3. Tc ser expression domains mark the position of developing appendage segments and shows that there is a mandible subcoxal segment..................87 Fig.3.4. Expression of Tc prd relative to Tc ser suggests that endites develop in the distal-most segment of the mandible, maxillary and labial protopodites............88

–  –  –

Fig.3.6. Expression of Tc ser and the PD domain genes in developing antennae......90 Fig.3.7. Two proximal domains of Tc ser expression in the developing maxilla could relate to the future segment boundary between the cardo and stipes............. 91

–  –  –

Fig.3.9. Timing of early expression domains of Tc ser suggest serial homology of subcoxa and coxa between different appendages.............................. 95

–  –  –

Fig.3.11. Similarity of expression domains of Tc ser relative to the PD domain genes in different post-antennal appendages suggests serial homology...................102

–  –  –

Fig.4.2. Expression of Tc cnc and Tc Dfd during Tribolium embryogenesis......... 119 Fig.4.3. Repression of Tc Dfd expression in the developing mandibular limb bud....120

–  –  –

Fig.4.5. Expression of Tc Dfd and mxp in the mandible and maxilla during embryogenesis relative to the endites marked by Tc prd expression..............122 Fig.4.6. Tc cncRNAi results in transformation of the mandibular into maxillary identity and deletion of the labrum................................................123 Fig.4.7. Homeotic transformation of the mandibular appendage to maxillary identity and deletion of the labrum in Tc cnc knock down embryos as revealed by the expression of Tc Dll and Tc prd.............................................125

–  –  –

Fig.5.3. Maxillary palp identity is maintained in the absence of Tc Dfd function.....150 Fig.5.4. Tc Dfd upregulates the proximal domain of Tc dac in the maxilla.......... 152 Fig.5.5. Tc Dfd patterns the endites of the mandibular and maxillary segments.....153

–  –  –

Fig.5.7. The mandible is transformed into antennal identity in Tc Dfd embryos.....156 Fig.6.1. Segmental expression patterns of the ten Hox genes of Cupiennius salei....165 Fig.6.2. Degenerate primers used to amplify homologue of cnc in Achaearanea....168 Fig.6.3. Alignment of translated 71bp sequence obtained by degenerate PCR with cnc orthologues from other arthropod taxa confirms identity as a CNC family member in Achaearanea........................................................... 169 Fig.6.4. Alignment of the bZIP domain of At cnc with other CNC and bZIP family members confirms that At cnc is a homologue of cnc.......................... 169 Fig.6.5. Expression of homologues of segment polarity gene engrailed and the PD domain gene Dll in Achaearanea embryos................................... 171

–  –  –

Fig.6.7. Comparison of the anterior expression boundary of Dfd homologues in Achaearanea and Tribolium homologises the mandibular segment to the first leg segment...............................................................172

–  –  –

Fig.7.3 Comparison of gene expression and gene regulation in the gnathocephalon, the mandibular, maxillary and labial segments of Tribolium and Drosophila........... 192

–  –  –



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