L'acquisition de la forme - ou morphogenèse - chez les systèmes vivants, est largement contrôlée par les gènes. Néanmoins, le lien précis entre, d'une part, les processus chimiques locaux associés aux gènes, et, d'autre part, la géométrie des tissus, n'est pas complètement identifié. Ce lien est vraisemblablement très indirect et médié par des processus mécaniques. Ainsi, il est aujourd'hui admis que les processus chimiques intracellulaires régulent les propriétés mécaniques des cellules seulement localement, et que la forme émerge comme la résolution globale de contraintes mécaniques. Ce paradigme, dit biomécanique, est employé dans cette thèse dans le cas de la morphogenèse des plantes, qui repose majoritairement sur la croissance cellulaire. Le contrôle local de cette croissance est crucial pour la stabilité et la robustesse de la morphogenèse, et implique différents mécanismes de régulation. En particulier, selon une hypothèse récente, les cellules pourraient adapter dynamiquement leur croissance en réponse aux forces qu'elles subissent.Cette régulation locale s'intègre à une échelle multicellulaire de manière non intuitive. Dans cette thèse, j'ai exploré i/ une formalisation mathématique de la régulation de la croissance par les contraintes mécaniques et ii/ le comportement macroscopique émergent d'un tel mécanisme. Pour cela, j'ai adopté une approche de modélisation multi-échelle basée sur une formulation mathématique continue de la croissance cellulaire (développée précédemment dans le cadre de la théorie de la morphoélasticité), et sur une description moyenne des processus moléculaires locaux étant supposés impliqués dans la mécano-perception et le contrôle de l'élasticité des cellules. J'ai d'autre part conçu des algorithmes dédiés à l'étude de ce modèle, intégrés dans un environnement logiciel existant, basé sur la méthode des éléments finis. Ce modèle est en particulier utilisé dans l'étude de la stabilité d'organes à fort degré d'asymétrie, tels que les feuilles, en suggérant qu'un contrôle de la croissance basé sur les forces peut permettre l'amplification d'asymétries initiales. / How do living objects acquire their shape? Incontrovertibly, morphogenesisis largely regulated by genes. Yet, the precise link between thechemical processes associated with genes, on the one hand, and geometry,one the other hand, is not completely identified. This link is most probablyindirect, and mediated by mechanical processes. It is now well acceptedthat intracellular molecular processes regulate locally cell mechanicalproperties and that shape emerges as the global resolution of resultingmechanical constraints.This so-called biomechanical paradigm is employed in this thesis in thecontext of plant morphogenesis, that mostly relies on cell growth. Thelocal control of growth is crucial for the stability and robustness ofmorphogenesis, and relies on various regulatory mechanisms. Inparticular, according to a recent hypothesis, cells may dynamicallyadapt their growth behavior in response to the mechanical forces theyexperience.This local regulation integrates at larger, multicellular scale, in anonintuitive way. In this thesis, I investigate i/ the mathematicalformalization of a stress-based control of growth and ii/ themacroscopic emergent behavior of such mechanism. To do so, I have used amultiscale modeling approach, based on a continuum mathematical modelof growth (previously developed within the theory of morphoelasticity),and on a mean description of the molecular processes supposedly involvedin mechanoperception and the control of cell elastic properties. Tostudy this model, I have designed dedicated algorithms, integrated into apreviously developed software environment, based on the finite elementmethod. This model is then used to study the mechanical stability ofhighly asymmetric organs like leaves, suggesting that a force-basedcontrol of growth allows the amplification of shape asymmetry duringdevelopment.

Morphogenesis, or the development of tissues, structures, and organs, is at the heart of embryonic development. Morphogenesis is a complex, multi-tissue process that requires coordinated cellular communication, migration, and differentiation; due to this complexity, the mechanisms that underlie morphogenesis remain poorly understood. The sea urchin embryo is morphologically and genetically more simple than most other developmental model organisms, and is optically transparent, making it a highly tractable system in which to study morphogenetic processes. The sea urchin larval endoskeleton is a biomineral that is secreted by primary mesenchyme cells (PMCs). The PMCs ingress into the embryo and remain individual, mesenchymal cells that migrate into a stereotypic three-dimensional (3-D) pattern within the blastocoel, prefiguring the form of the ensuing skeleton, which they subsequently secrete. PMC positioning is directed by cues originating in the overlying ectoderm; however, the molecular identity of those cues has remained unknown. The work described in this dissertation combines systems-level approaches with in vivo 3-D spatial analysis to identify novel skeletal patterning genes and to define their functional roles in skeletal patterning. A transcriptomics-based screen identified numerous novel candidate skeletal patterning cues. Of those cues, two were further pursued for detailed functional studies. First, the sulfate transporter SLC26a2/7 (SLC) was found to promote ventral accumulation of sulfated proteoglycans that is both necessary and sufficient to attract PMCs to the ventral territory for ventral skeleton formation. Second, the enzyme 5-lipoxygenase (LOX) was found to be required for ventral and rotational skeletal patterning, and its product, 5(S)-HETE was found to be a chemoattractant for PMCs, thereby identifying a novel role for lipoxygenase enzymes in embryonic patterning and morphogenesis. Recent work from other groups has demonstrated that PMCs diversify their gene expression profiles during skeletal patterning, implying that PMC diversification is involved in skeletal patterning, likely as a response to locally distinct spatial cues. The studies herein identify Tbx2/3 and Pks2 as important PMC subset-specific genes whose spatial expression is modulated by SLC and LOX, respectively. Together, these results provide new mechanistic insights that define our molecular understanding of the regulation of sea urchin ventral skeletal patterning.

Invasive fungal infections are a significant clinical challenge especially for hospitalized patients as traditional antifungal therapy often fails to resolve these infections. The ability of Candida to undergo yeast-to-hyphae morphological transition is central to this invasive behavior. Morphogenesis is also important for the formation of biofilms which are highly structured communities of microorganisms attached to one another or substratum and embedded within a protective extracellular matrix material. The refractory nature of cells within a biofilm to current antifungal therapies has created a need for alternative antifungal agents for the management of Candida biofilm-related infections. The novel antifungal occidiofungin is a natural product produced by the soil bacteria Burkholderia contaminans shown to be effective against a broad range of fungi including Candida spp. Prior studies have demonstrated that occidiofungin inhibits yeast-to-hyphae morphogenesis in the dimorphic yeast, C. albicans, likely through its impact on disrupting F-actin organization. To extend these findings, the efficacy of occidiofungin on morphogenesis of C. albicans and C. tropicalis strains under different inducing conditions was evaluated. Further, given the role of biofilm on pathogenicity, the anti-biofilm properties of occidiofungin against Candida species was examined using an in vitro static biofilm model developed on a silicon elastomer disk. The accumulated data indicate that occidiofungin inhibits hyphal transformation regardless of the inducing conditions used and prevents hyphal extension when added to cells post switching. Moreover, morphologically switching cells were more sensitive to occidiofungin than their yeast counterpart. In addition, occidiofungin effectively blocks biofilm formation at all stages of development and reduces dispersed cells from the biofilm for both C. albicans and C. tropicalis. Confocal data revealed alterations in actin organization with occidiofungin treatment for both morphologically switching and biofilm cells. These findings correlate with prior observations for occidiofungin activity on yeast form cells indicating the broad activity of occidiofungin against fungi at various stages of pathogenic growth and supports efforts to pursue occidiofungin as a potential therapeutic against Candida based infections.

Indiana University-Purdue University Indianapolis (IUPUI) / Even though the molecular events and pathways that underlie craniofacial development and morphogenesis are not fully understood, it is accepted that their orchestration is influenced by the interaction of genetic and environmental factors. Inbred mouse strains represent genetically homogenous groups of individuals. It is established that mice in one strain often differ quite remarkably from mice in other inbred strains. Those phenotypic differences make mice exceptional tools for the dissection of genetic factors that influence normal and abnormal craniofacial morphogenesis. While numerous investigations have focused on abnormal morphogenesis, a comprehensive study of normal craniometric morphology across multiple inbred strains of mice has not been previously performed. The Mouse Phenome Project, an international collaboration of investigators, was formed to systematically phenotype a collection of normal inbred mouse strains. The objectives of our studies were to determine and measure differences in quantitative mandibular traits/variables within and between different inbred mouse strains, and to assess sexual di1norphism through bilateral measuren1ents of the hemimandibles. These studies were a component of the Mouse Phenome Project to collect normal craniometric data from 12 genetically heterogeneous inbred strains utilizing digital images from equal numbers of female and male mice at 7 to 8 weeks of age. Our central hypothesis was that morphometric analysis of mandibular structures from genetically disparate inbred mouse strains would reveal quantifiable differences. The null hypothesis of no difference among the strains for 1nandibular measurements was rejected. Overall, CAST/Ei and MOLF/Ei were consistently small in size measured by body weight with small skeletal structures. There was no strong pattern of body weight and site of skeletal size in the mid and heavy weighted strains. Evidence of sexual dimorphism was supported. Overall, it appears males and females that have the least significance between them are in the DBA/2J strain, followed by A/J. The strain with the most significant difference between males and females is in the C3H/HeJ strain.

The Stubble-stubbloid locus encodes a transmembrane serine protease (Stubble) necessary for the proper formation of sensory bristles, and the morphogenesis of leg and wing epithelia. Genetic and cell biological analysis indicate a role for Stubble in actin cytoskeletal dynamics and cell shape changes in developing epithelia and bristles. Previously reported genetic interactions between Stubble and the Rho1 signaling pathway suggest Stubble influences actin cytoskeleton dynamics in developing imaginal discs through interactions with the Rho1 pathway. This work will discuss a genetic screen conducted to further investigate the role of Stubble in bristle and imaginal disc morphogenesis. From 50,000 EMS-mutagenized chromosomes 12 enhancers of the recessive sbd201 allele were identified, including 6 new sbd alleles. Consistent with the current understanding of genetic interactions regulating imaginal disc morphogenesis, mutations in two Rho1 pathway genes, zipper (2 alleles) and Rho1, were isolated. Additionally, three new mutant enhancers of sbd201 were isolated, one of which has been identified as an allele of the cadherin gene Dacshous, another as an allele of the muscle myosin heavy chain gene, and the last as an allele of Notopleural (Np). Dominant and recessive mutations in the Stubble locus interact with the Np allele identified in this screen, in regards to both limb and bristle development, respectively. Mutations in the Np locus were first identified in 1936, but this locus remains poorly characterized and has never been cloned The genetic and phenotypic characterization of Np will be discussed along with experiments that have mapped the position of the Np locus to a 50kb region at the border of the 44F12, 45A1 cytological regions.

Indiana University-Purdue University Indianapolis (IUPUI) / Even though the molecular events and pathways that underlie craniofacial development and morphogenesis are not fully understood, it is accepted that their orchestration is influenced by the interaction of genetic and environmental factors. Inbred mouse strains represent genetically homogenous groups of individuals. It is established that mice in one strain often differ quite remarkably from mice in other inbred strains. Those phenotypic differences make mice exceptional tools for the dissection of genetic factors that influence normal and abnormal craniofacial morphogenesis. While numerous investigations have focused on abnormal morphogenesis, a comprehensive study of normal craniometric morphology across multiple inbred strains of mice has not been previously performed. The Mouse Phenome Project, an international collaboration of investigators, was formed to systematically phenotype a collection of normal inbred mouse strains. The objectives of our studies were to determine and measure differences in quantitative mandibular traits/variables within and between different inbred mouse strains, and to assess sexual dimorphism through bilateral measurements of the hemimandibles. These studies were a component of the Mouse Phenome Project to collect normal craniometric data from 12 genetically heterogeneous inbred strains utilizing digital images from equal numbers of female and male mice at 7 to 8 weeks of age. Our central hypothesis was that morphometric analysis of mandibular structures from genetically disparate inbred mouse strains would reveal quantifiable differences. The null hypothesis of no difference among the strains for mandibular measurements was rejected. Overall, CAST/Ei and MOLF/Ei were consistently small in size measured by body weight with small skeletal structures. There was no strong pattern of body weight and site of skeletal size in the mid and heavy weighted strains. Evidence of sexual dimorphism was supported. Overall, it appears males and females that have the least significance between them are in the DBA/2J strain, followed by A/J. The strain with the most significant difference between males and females is in the C3H/HeJ strain.

No description available.

No description available.

No description available.

<p> Caenorhabditis elegans (C. elegans) is a model organism which is known for its transparent body, small body size, high reproductivity and short lifecycle. Several important genes and signal transduction pathways are well conserved in C. elegans. lin//, a LIM homeobox family member, plays a crucial role in the development of the vulva in C. elegans. LIM homeobox genes are a subgroup of Homeobox family that play fundemental role in animal development. In C. elegans lin-If mutant animals fail to form a functional vulva and vulval-uterine connection and consequently exhibit egg-laying defective phenotype. The cell lineage and marker gene expression studies have shown that lin-// is required for the patterning of all primary and secondary lineage vulval cells. lin- II also functions in the nervous system. </p> <p> lin-// expression is mainly observed in the developing vulval cells and in the pi cells which are involved in the formation of vulval-uterine connection. lin-If expression is also seen in VCs and in some of the head and tail neurons. The completed genome sequences of closely related species in Caenorhabditis genus serve as a power tool to do systematic comparative studies. The lin-If regulatory sequences from these species have been compared along with the expression patterns. </p> <p> We looked at the regulation of lin-// in closely related nematode species like C. elegans, C. briggsae, C. remanei and Caenorhabditis n species. </p> <p> Consistent with this. expression of lin-11 is observed in the developing vulval cells. We are interested in understanding evolutionary changes in the regulation and function of lin-II in reproductive system </p> <p> /in-11 is a LIM homeodomain family member which IS involved in several developmental events. lin-11 role is documented in the thermoregulatory circuit specifying AIY interneuron, in chemosensory neurons like A W A and olfactory neurons A WS. During vulval development lin-II expression is dynamically expressed in subset of secondary lineage cells and is broadly expressed in all the cells indicating its role in cell identity and cell fusion of the vulval cells. lin-II is also required for the formation of vulval uterine connection which is the passage to lay eggs in the hermaphrodite. linllloss of function hermaphrodites have change in the axis of the secondary lineage cells during vulval development, uterine Jt cell migration defect, defects in the AIY, A W A and A WS interneurons resulting in egg-laying defect and protruding vulva and neuronal defects and reduced mating efficiency. </p> <p> The expression pattern of lin-If in closely related species is highly similar but not identical. From the sequence comparison of lin-If regulatory sequences a 1 kb conserved block of sequences have been identified which includes the regulatory sequences responsible for the expression of lin-If in vulva and Jt cells. We propose that cisregulatory elements controlling lin-If gene expression are slowly evolving though there is no change in the function which indicates that lin-If plays critical role during the development of the vulva and other tissues. </p> / Thesis / Master of Science (MSc)