Abstract
BackgroundOrganisms show an incredibly diverse array of body and organ shapes that are both unique to their taxon and important for adapting to their environment. Achieving these specific shapes involves coordinating the many processes that transform single cells into complex organs, and regulating their growth so that they can function within a fully-formed body.Main textConceptually, body and organ shape can be separated in two categories, although in practice these categories need not be mutually exclusive. Body shape results from the extent to which organs, or parts of organs, grow relative to each other. The patterns of relative organ size are characterized using allometry. Organ shape, on the other hand, is defined as the geometric features of an organ’s component parts excluding its size. Characterization of organ shape is frequently described by the relative position of homologous features, known as landmarks, distributed throughout the organ. These descriptions fall into the domain of geometric morphometrics.ConclusionIn this review, we discuss the methods of characterizing body and organ shape, the developmental programs thought to underlie each, highlight when and how the mechanisms regulating body and organ shape might overlap, and provide our perspective on future avenues of research.
Highlights
Body and organ shape can be separated in two categories, in practice these categories need not be mutually exclusive
The patterns described by changes in relative size between organs are known to specialists in this field as allometry [6, 7]
Studies over the past twenty years, primarily from insects, have highlighted key genetic pathways required for regulating body size and relative organ size [2, 4, 17,18,19,20]
Summary
Quantifying variation in body and organ shape A number of excellent reviews describe and compare the methodologies used to study body shape, including metrics for describing allometric patterns, and organ shape, the realm of geometric morphometrics [5, 26,27,28]. Integrins play central roles in tubular growth directed by tip cells in many other animals, such as the renal tubes of D. melanogaster [89], vertebrate angiogenesis [90, 91], and the development of the branched respiratory systems in mammals and insects [92, 93] How this mechanism of growth regulation scales across organ and body sizes is poorly understood. The Dpp gradient in the D. melanogaster wing regulates growth and establishes boundaries of gene expression that are essential for the correct specification and positioning of the veins along the wing [166] In this way, morphogens regulate the relative size of organs, they regulate organ shape by controlling the identity, position, and behaviour of cell types within an organ. Future studies comparing the how size and shape mechanisms evolve will help to elucidate how the diversity of body and organ shapes have arisen
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