Publication

Temporal colinearity and the phylotypic progression: a basis for the stability of a vertebrate Bauplan and the evolution of morphologies through heterochrony

Denis Duboule
1994
Journal paper
Abstract

Vertebrate Hox genes are essential for the proper organization of the body plan during development. Inactivation of these genes usually leads to important alterations, or transformations, in the identities of the affected developing structures. Hox genes are activated in a progressive temporal sequence which is colinear with the position of these genes on their respective complexes, so that 'anterior' genes are activated earlier than 'posterior' ones (temporal colinearity). Here, an hypothesis is considered in which the correct timing of activation of this gene family is necessary in order to properly establish the various expression domains. Slight modifications in the respective times of gene activation (heterochronies) may shift expression domains along the rostrocaudal axis and thus induce concurrent changes in morphologies. It is further argued that temporal colinearity only occurs in cells with high mitotic rates, which results in a strong linkage between patterning and growth control and makes the patterning process unidirectional, from anterior, proximal and early, to posterior, distal and late, a model referred to as the 'Einbahnstrasse'. While the nature of the mechanism(s) behind temporal and spatial colinearities is unknown, it is proposed that such a mechanism relies on meta-cis interactions, that is it may necessitate gene contiguity. Such a mechanism would be based on DNA-specific, rather than gene-specific, features such as chromatin configurations or DNA replication. The existence of such a meta-cis mechanism would explain the extraoridinary conservation of this genetic system during evolution as its basic properties would be linked to that of the genetic material itself.(ABSTRACT TRUNCATED AT 250 WORDS)

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Related concepts (36)
Hox gene
Hox genes, a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. Hox proteins encode and specify the characteristics of 'position', ensuring that the correct structures form in the correct places of the body. For example, Hox genes in insects specify which appendages form on a segment (for example, legs, antennae, and wings in fruit flies), and Hox genes in vertebrates specify the types and shape of vertebrae that will form.
Gene
In biology, the word gene (from γένος, génos; meaning generation or birth or gender) can have several different meanings. The Mendelian gene is a basic unit of heredity and the molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protein-coding genes and noncoding genes. During gene expression, the DNA is first copied into RNA. The RNA can be directly functional or be the intermediate template for a protein that performs a function.
Body plan
A body plan, Bauplan (), or ground plan is a set of morphological features common to many members of a phylum of animals. The vertebrates share one body plan, while invertebrates have many. This term, usually applied to animals, envisages a "blueprint" encompassing aspects such as symmetry, layers, segmentation, nerve, limb, and gut disposition. Evolutionary developmental biology seeks to explain the origins of diverse body plans.
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