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AMERICAN ASSOCIATION OF ANATOMISTS SPONSORED
STUDENT SATELLITE SYMPOSIUM 2009

Gene regulation: An Eco-Evo-Devo perspective

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ABSTRACTS

Physical mechanisms in the development and evolution of the vertebrate limb

STUART A. NEWMAN
Department of Cell Biology and Anatomy, New York Medical College, Valhalla, NY USA

The development of the vertebrate limb depends on two distinct processes that also represented innovations in the history of the chordates. The first is the formation of fin or limb buds as extensions of the body wall. The second is the formation within the limb bud mesenchyme of rods and nodules of cartilage comprising the primordia of the endoskeleton. In both cases gene products of the relevant tissues mobilize physical forces and effects to mediate morphogenesis and pattern formation. The avian limb bud, for example, is initiated when changes in extracellular matrix and cytoskeleton in the mesenchyme subjacent to the apical ectodermal ridge (AER) cause it to become more cohesive and mechanically passive relative to the surrounding flank. The endoskeleton forms by the interplay of activating and inhibitory signals for precartilage condensation, constituting a self-organizing "reaction-diffusion"-type system generating arrays of discrete skeletal elements. The number, arrangement and character of endoskeletal elements depend on the size and shape of the limb bud, but in a nonlinear fashion. Thus, while the limb bud is subject to gradual reshaping over the course of evolution by incremental variations in its underlying gene regulatory network, the corresponding skeletal patterns can undergo abrupt changes, leading to morphological novelties.

 

Evolution of the gene network underlying wing polyphenism in the hyperdiverse genus Pheidole

EHAB ABOUHEIF(1), RAJENDHRAN RAJAKUMAR*(1), MISCHA DIJKSTRA(2), DIEGO SAN MAURO(3), MING HUANG(4), FRANCOIS HIOU-TIM(1), DIANA WHEELER(4), MICHAEL COURNEYEA(1) AND ABDERRAHMAN KHILA(1)
1. Department of Biology, McGill University, Montreal, Quebec
2. Department of Ecology and Evolution, University of Lausanne, Switzerland
3. Department of Zoology, The Natural History Museum, London, UK
4. Department of Entomology, University of Arizona, USA

Wing polyphenism is the ability of the regulatory gene networks that underlie wing development in ants to either produce a queen with fully functional wings or a worker that is completely wingless depending on environmental cues such as temperature, nutrition, and photoperiod. Although wing polyphenism is a homologous and nearly universal feature among ants, the gene network that underlies wing polyphenism has evolved. To understand which forces drive the evolution of this gene network, we performed an integrated analysis including colony-level behavior, embryology, endocrinology, gene expression, and phylogeny of species within the hyperdiverse ant genus Pheidole. We present evidence that the gene network may have evolved both through "genetic accommodation" of a novel worker caste as well as through genetic drift. This is the first example of gene network evolution by genetic accommodation and drift, and may be a general feature of gene networks that underlie plastic phenotypes in nature.

 

An eco-evo-devo approach to the study of phenotypic diversity by combining population history and gene networks: The case study of Monomorium emersoni in the Arizona Sky Islands

MARIE-JULIE FAVE AND EHAB ABOUHEIF
Department of Biology, McGill University, Montreal, Quebec

The independent evolution and maintenance of similar morphologies has been a source of interest in evolutionary biology for decades as it provides a naturally replicated experiment from which the processes implicated in the generation of novel phenotypic diversity can be unravelled. As a diverse array of processes acting at different spatial and temporal scales are involved in the generation of novelty, I propose to use an integrative approach incorporating population genetics along with analyses of gene regulatory networks that underlie morphological variation. I will present how the study of queen winglessness evolution in the ant M. emersoni inhabiting the Arizona Sky Islands is perfectly suited to reach this overall goal. I will first present my results on phylogeography, population structure and demography to infer the past and recent history of the species. I will focus on how the environmental conditions vary spatially (different altitudes) and temporally (Pleistocene climatic fluctuations) to shape this species' pattern of distribution and how this relates to its polymorphism. I will then present preliminary gene expression data of specific genes involved in the wing patterning network that could be involved in interrupting the wing formation. I will conclude on future directions that will be taken in the course of this project.

 

Assembly reflects evolution of protein complexes

EMMANUEL LEVY(1,3), ELISABETTA BOERI ERBA(2), CAROL ROBINSON(2) AND SARAH A. TEICHMANN(1)
1.MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK
2. Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UK
3. Present address: UniversitŽ de Montreal, Biochemistry department, Montreal, Canada

A homomer is formed by self-interacting copies of a protein unit. This is functionally important, as in allostery, and structurally crucial because mis-assembly of homomers is implicated in disease. Homomers are widespread, with ~50 of proteins with a known quaternary state assembling into such structures. Despite their prevalence, little is known about the mechanisms that drive their formation, both at the level of evolution and assembly in the cell. Here we present an analysis of over 5,000 unique atomic structures and show that the quaternary structure of homomers is conserved in over 70% of protein pairs sharing as little as 30% sequence identity. Where quaternary structure is not conserved, a detailed investigation revealed well-defined evolutionary pathways by which proteins transit between different quaternary structure types. Furthermore, we show by perturbing subunit interfaces within complexes and by mass spectrometry analysis, that the (dis)assembly pathway mimics the evolutionary pathway. These data represent a molecular analogy to Haeckel's evolutionary paradigm of embryonic development, where an intermediate in the assembly of a complex represents a form that appeared in its own evolutionary history. Our model of self-assembly allows reliable prediction of evolution and assembly of a complex solely from its crystal structure.

 

Hormones and development: Deciphering the regulatory architecture underlying life-history transitions and their evolution

ANDREAS HEYLAND
University of Guelph, Integrative Biology, Guelph, ON, Canada

Life history transitions in animals and plants are complex developmental processes that are tightly integrated with the organisms ecology and physiology and that are frequently regulated by hormones. While this raises fascinating questions about the evolution of signalling mechanisms involved in life history transitions, it also reveals a remarkable lack of information on mechanisms underlying hormonal signalling systems in many invertebrate groups, specifically marine invertebrates from which a diverse array of developmental modes are known. I will discuss two examples of marine invertebrate species with complex life histories from which we were recently able to expand our knowledge on endocrine and neuroendocrine signalling systems involved in larval development and metamorphosis. The first example summarizes new data on thyroid hormone-like signalling in sea urchin development and the second example will focus on regulatory mechanisms involved in development and neurogenesis of the sea hare Aplysia californica. I conclude that endocrine and neuroendocrine mechanisms in marine invertebrate groups require more attention and will discuss how comparisons with for example insect and amphibian life histories and their regulation via hormones can help to elucidate mechanisms underlying life history evolution in general.

 

Patterns and processes of avian digit reduction

AUDREY HEPPLESTON*, GEMMA DEMARTINO**, HANS CE LARSSON*
*Redpath Museum, McGill University, Montreal, Quebec
**Institut de Recherche Clinique de Montreal, Montreal, Quebec

Birds offer the possibility to study digit reduction since most of them only ossify 3 digits in the adult wing compared to their pentadactyl dinosaurian ancestors. Some avian species such as the emu pushed limb reduction further, having only one ossified digit in the wing. Patterns and processes of digit number reduction have been investigated by comparing these taxa to other groups having the common pattern of 5 digits. Precartilogenic condensations have been visualized in limb sections to compare the early patterning of the limb in chick, emu, alligator and mouse. This allows us to identify potential differences with previously described chondrification sequences, as well as comparing early patterning between mammals and archosaurs. We have also investigated potential developmental differences though in-situ hybridization and TUNEL analysis. Key genes in limb patterning were observed in emu, chick and mouse. More specifically, the quantitative expression profiles of Shh have been compared in these species using real time PCR. These experiments show that very early events may be responsible for the reduction of the emu autopodium. Furthermore, expression profiles have been shown to be different between all the species studied, which informs us of potential means by which different digit numbers may have evolved in birds.

 

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