Cell lineage transport: a mechanism for molecular gradient formation

Gradient formation is a fundamental patterning mechanism during embryo development, commonly related to secreted proteins that move along an existing field of cells. Here, we mathematically address the feasibility of gradients of mRNAs and non-secreted proteins. We show that these gradients can arise in growing tissues whereby cells dilute and transport their molecular content as they divide and grow, a mechanism we termed ‘cell lineage transport.' We provide an experimental test by unveiling a distal-to-proximal gradient of Hoxd13 in the vertebrate developing limb bud driven by cell lineage transport, corroborating our model. Our study indicates that gradients of non-secreted molecules exhibit a power-law profile and can arise for a wide range of biologically relevant parameter values. Dilution and nonlinear growth confer robustness to the spatial gradient under changes in the cell cycle period, but at the expense of sensitivity in the timing of gradient formation. We expect that gradient formation driven by cell lineage transport will provide future insights into understanding the coordination between growth and patterning during embryonic development

Anatomical Network Comparison of Human Upper and Lower, Newborn and Adult, and Normal and Abnormal Limbs, with Notes on Development, Pathology and Limb Serial Homology vs. Homoplasy

How do the various anatomical parts (modules) of the animal body evolve into very different integrated forms (integration) yet still function properly without decreasing the individual's survival? This long-standing question remains unanswered for multiple reasons, including lack of consensus about conceptual definitions and approaches, as well as a reasonable bias toward the study of hard tissues over soft tissues. A major difficulty concerns the non-trivial technical hurdles of addressing this problem, specifically the lack of quantitative tools to quantify and compare variation across multiple disparate anatomical parts and tissue types. In this paper we apply for the first time a powerful new quantitative tool, Anatomical Network Analysis (AnNA), to examine and compare in detail the musculoskeletal modularity and integration of normal and abnormal human upper and lower limbs. In contrast to other morphological methods, the strength of AnNA is that it allows efficient and direct empirical comparisons among body parts with even vastly different architectures (e.g. upper and lower limbs) and diverse or complex tissue composition (e.g. bones, cartilages and muscles), by quantifying the spatial organization of these parts-their topological patterns relative to each other-using tools borrowed from network theory. Our results reveal similarities between the skeletal networks of the normal newborn/adult upper limb vs. lower limb, with exception to the shoulder vs. pelvis. However, when muscles are included, the overall musculoskeletal network organization of the upper limb is strikingly different from that of the lower limb, particularly that of the more proximal structures of each limb. Importantly, the obtained data provide further evidence to be added to the vast amount of paleontological, gross anatomical, developmental, molecular and embryological data recently obtained that contradicts the long-standing dogma that the upper and lower limbs are serial homologues. In addition, the AnNA of the limbs of a trisomy 18 human fetus strongly supports Pere Alberch's ill-named "logic of monsters" hypothesis, and contradicts the commonly accepted idea that birth defects often lead to lower integration (i.e. more parcellation) of anatomical structures

Organización caótica en los Baupläne de Bilateria: simetría y complejidad animal

[EN] The body plan of bilateral animals is characterized by the early specification of three embryonic axes. One of these axes defines the plane of bilateral symmetry of the future adult, ideally dividing these organisms in two mirror-image halves, left and right. Most species of this group exhibit significant and robust departures from this ideal bilateral plan, showing a suite of asymmetric characters. This paper characterizes different patterns and processes of asymmetry, highlighting both phylogenetic and ontogenetic aspects of such a basic feature of Bilateria. In addition, the role of symmetry and asymmetry as a way to increase the amount of complexity in animal organization is explored[ES] El Bauplan de los animales bilaterales se caracteriza por la demarcación en estadíos tempranos de tres ejes embrionarios. Uno de estos ejes define el plano de simetría bilateral del futuro adulto, el cual divide a estos organismos, en teoría, en dos mitades especulares: izquierda y derecha. Las especies de este grupo se distancian de un modo significativo y robusto de ese Bauplan bilateral ideal, exhibiendo un conjunto de caracteres asimétricos. Este artículo caracteriza los diferentes patrones y procesos en donde se presenta la asimetría, destacando aspectos tanto filogenéticos como ontogenéticos de esta característica básica de los Bilateria. Se apunta, también, el posible papel de la simetría y la asimetría como vehículos para incrementar la cantidad de complejidad en la organización animal.This paper has been partly funded by grant PB98- 0813 of the DGYCIT.Peer reviewe

Organized mayhem in Bilateria Baupläne: symmetry and animal complexity

The body plan of bilateral animals is characterized by the early specification of three embryonic axes. One of these axes defines the plane of bilateral symmetry of the future adult, ideally dividing these organisms in two mirror-image halves, left and right. Most species of this group exhibit significant and robust departures from this ideal bilateral plan, showing a suite of asymmetric characters. This paper characterizes different patterns and processes of asymmetry, highlighting both phylogenetic and ontogenetic aspects of such a basic feature of Bilateria. In addition, the role of symmetry and asymmetry as a way to increase the amount of... (Ver más) complexity in animal organization is explored.El Bauplan de los animales bilaterales se caracteriza por la demarcación en estadíos tempranos de tres ejes embrionarios. Uno de estos ejes define el plano de simetría bilateral del futuro adulto, el cual divide a estos organismos, en teoría, en dos mitades especulares: izquierda y derecha. Las especies de este grupo se distancian de un modo significativo y robusto de ese Bauplan bilateral ideal, exhibiendo un conjunto de caracteres asimétricos. Este artículo caracteriza los diferentes patrones y procesos en donde se presenta la asimetría, destacando aspectos tanto filogenéticos como ontogenéticos de esta característica básica de los Bilateria.... (Ver más) Se apunta, también, el posible papel de la simetría y la asimetría como vehículos para incrementar la cantidad de complejidad en la organización animal

Modelos geométricos y topológicos en morfología. Exploración de los límites del morfoespacio afín : aplicaciones en paleobiología

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Biología. Fecha de lectura: 05-12-199

Morphologie théorique de réseaux crâniens de tétrapodes

Les modèles de réseaux crâniens dans lesquels les nœuds représentent les os et les liaisons les sutures ont récemment permis d’apporter un nouveau regard sur les contraintes structurales qui sous-tendent la réduction évolutive du nombre d’os du crâne des tétrapodes, connue sous le nom de loi de Williston. Ici ont été construits des espaces morphologiques génératifs de crânes de tétrapodes, dérivés d’un modèle de réseau nul utilisant des lois de croissance à liaison préférentielle et proximité géométrique aléatoires. Nos résultats indiquent que la proximité géométrique est le meilleur modèle nul qui permette d’expliquer la disparité des structures crâniennes sous une double contrainte : symétrie bilatérale et présence d’os non appariés. L’analyse de l’occupation temporelle de cet espace morphologique qu’explique la loi de Williston indique que le crâne de tétrapode a suivi un itinéraire évolutif vers des organisations morphologiques davantage contraintes.Network models of the tetrapod skull in which nodes represent bones and links represent sutures have recently offered new insights into the structural constraints underlying the evolutionary reduction of bone number in the tetrapod skull, known as Williston\u27s Law. Here, we have built null network model-derived generative morphospaces of the tetrapod skull using random, preferential attachment, and geometric proximity growth rules. Our results indicate that geometric proximity is the best null model to explain the disparity of skull structures under two structural constraints: bilateral symmetry and presence of unpaired bones. The analysis of the temporal occupation of this morphospace, concomitant with Williston\u27s Law, indicates that the tetrapod skull has followed an evolutionary path toward more constrained morphological organizations.</p

Anatomical Network Analysis in Evo-Devo

Editors: Laura Nuño de la Rosa, Gerd B. Müller.This chapter introduces the reader to anatomical network analysis (AnNA): a conceptual framework for the tolopological analysis of organismal form. AnNA focuses on the structural relations among anatomical parts, which allows for an evaluation of morphological organization in comparative analyses for both development and evolution. The nodes of the network represent anatomical elements, and the links that connect them represent structural relations or interactions among these elements. Network theory provides the methods to analyze these anatomical network models. The first and second sections present the historical and conceptual background of this framework. The third section explains the construction of anatomical networks and some of the basic parameters we can use to characterize the topology of these models and infer their morphological organization. The fourth section summarizes the interpretation of network parameters in terms of morphological complexity, hierarchy, integration, and modularity in the context of morphological evo-devo. The fifth section introduces the classical construction rules to build null models for networks and an example of the use of network null models in morphology. Finally, in the sixth section, we have explored some of the limits of AnNA.BE-A is funded by a European Union’s Horizon 2020 Marie Skłodowska-Curie Grant No. 654155. DRG is funded by MINECO-FEDER BFU2015-70927-R

Concept of Burden in Evo-Devo

Editors: Laura Nuño de la Rosa, Gerd B. Müller.The concept of burden was developed around the 1970s by Austrian zoologist Rupert Riedl, based on morphological insights rooted in Karl Ernst von Baer’s embryological tradition. Burden’s main tenet is that as a morphological character evolves, it develops more relationships with other characters, becoming more and more interconnected. Through this process, the morphological character acquires more biological “responsibilities” within the organism. Two main consequences of the burden hypothesis are that (1) a character’s evolvability will be limited by these responsibilities and (2) a set of heavily burdened characters could be considered as part of the body plan of a taxonomic group. The concept of burden is intimately related to that of developmental constraint, and as such, it is central to evo-devo.DRG funded by MINECO-FEDER BFU2015-70927-R. BE-A is funded by a European Union’s Horizon 2020 Marie Skłodowska-Curie grant No. 654155