Patterning of the Vertebrate Head in Time and Space by BMP Signaling.

How head patterning is regulated in vertebrates is yet to be understood. In this study, we show that frog embryos injected with Noggin at different blastula and gastrula stages had their head development sequentially arrested at different positions. When timed BMP inhibition was applied to BMP-overexpressing embryos, the expression of five genes: (a marker of the cement gland, which is the front-most structure in the frog embryo), (a forebrain marker), (a forebrain and mid-brain marker), (an anterior hindbrain marker), and (a posterior hindbrain marker) were sequentially fixed.

A Tribute to Lewis Wolpert and His Ideas on the 50th Anniversary of the Publication of His Paper 'Positional Information and the Spatial Pattern of Differentiation'. Evidence for a Timing Mechanism for Setting Up the Vertebrate Anterior-Posterior (A-P) Axis.

This article is a tribute to Lewis Wolpert and his ideas on the occasion of the recent 50th anniversary of the publication of his article 'Positional Information and the Spatial Pattern of Differentiation'. This tribute relates to another one of his ideas: his early 'Progress Zone' timing model for limb development. Recent evidence is reviewed showing a mechanism sharing features with this model patterning the main body axis in early vertebrate development.

Some Questions and Answers About the Role of Temporal Collinearity in Vertebrate Axial Patterning.

The vertebrate anterior-posterior (A-P = craniocaudal) axis is evidently made by a timing mechanism. Evidence has accumulated that tentatively identifies the A-P timer as being or involving temporal collinearity (TC). Here, I focus on the two current competing models based on this premise.

What are the roles of retinoids, other morphogens, and Hox genes in setting up the vertebrate body axis?

This article is concerned with the roles of retinoids and other known anterior-posterior morphogens in setting up the embryonic vertebrate anterior-posterior axis. The discussion is restricted to the very earliest events in setting up the anterior-posterior axis (from blastula to tailbud stages in Xenopus embryos). In these earliest developmental stages, morphogen concentration gradients are not relevant for setting up this axis.

Two Tier Hox Collinearity Mediates Vertebrate Axial Patterning.

A two tier mechanism mediates Hox collinearity. Besides the familiar collinear chromatin modification within each Hox cluster (nanocollinearity), there is also a macrocollinearity tier. Individual Hox clusters and individual cells are coordinated and synchronized to generate multiscale (macro and nano) collinearity in the early vertebrate embryo.

Spiral waves and vertebrate embryonic handedness.

During early embryonic development, the vertebrate main body axis is segmented from head-to-tail into somites. Somites emerge sequentially from the presomitic mesoderm (PSM) as a consequence of oscillatory waves of genetic activity, called somitogenesis waves. Here, we discuss the implications of the dynamic patterns of early X-Delta-2 expression in the prospective somites (somitomeres) of Xenopus laevis.

A tribute to D'Arcy Wentworth Thompson: Elucidation of a developmental principle.

We show the vertebrate anterior -posterior axis is made by time space translation (TST). 1/ TST of Hox temporal to spatial collinearity makes the trunk part of the axis. 2/TST continues into the head.

Collinear Hox-Hox interactions are involved in patterning the vertebrate anteroposterior (A-P) axis.

Investigating regulation and function of the Hox genes, key regulators of positional identity in the embryo, opened a new vista in developmental biology. One of their most striking features is collinearity: the temporal and spatial orders of expression of these clustered genes each match their 3' to 5' order on the chromosome. Despite recent progress, the mechanisms underlying collinearity are not understood.

Vertical signalling involves transmission of Hox information from gastrula mesoderm to neurectoderm.

Development and patterning of neural tissue in the vertebrate embryo involves a set of molecules and processes whose relationships are not fully understood. Classical embryology revealed a remarkable phenomenon known as vertical signalling, a gastrulation stage mechanism that copies anterior-posterior positional information from mesoderm to prospective neural tissue. Vertical signalling mediates unambiguous copying of complex information from one tissue layer to another.

Dislocation is a developmental mechanism in Dictyostelium and vertebrates.

The excitable cells of Dictyostelium discoideum show traveling waves of signaling and generate a variety of complex wave forms during their morphogenesis. Important among these wave forms is the 3D spiral or scroll wave, which has been proposed previously to have a twisted variant: the "turbine wave." Herein we argue that a D.

Hox collinearity - a new perspective.

Hox collinearity is a spectacular phenomenon that has excited life scientists since its discovery in 1978. Two mechanisms have been proposed to explain the spatially sequential pattern of Hox gene expression in animal embryonic development: interactions among Hox genes, or the progressive opening of chromatin in the Hox clusters, from 3' to 5'. A review of the evidence across different species and developmental stages points to the universal involvement of trans-acting factors and cell-cell interactions.

Analyzing the function of a hox gene: an evolutionary approach.

We present an evolutionary approach to dissecting conserved developmental mechanisms. We reason that important mechanisms for making the bodyplan will act early, to generate the major features of the body and that they will be conserved in evolution across many metazoa, and thus, that they will be available in very different animals. This led to our specific approach of microarrays to screen for very early conserved developmental regulators in parallel in an insect, Drosophila and a vertebrate, Xenopus.

XMeis3 is necessary for mesodermal Hox gene expression and function.

Hox transcription factors provide positional information during patterning of the anteroposterior axis. Hox transcription factors can co-operatively bind with PBC-class co-factors, enhancing specificity and affinity for their appropriate binding sites. The nuclear localisation of these co-factors is regulated by the Meis-class of homeodomain proteins.

Retinoid signalling is required for information transfer from mesoderm to neuroectoderm during gastrulation.

The hindbrain region of the vertebrate central nervous system (CNS) presents a complex regionalisation. It consists of 7-8 distinct morphological segments called rhombomeres, each with a unique identity provided by combinations of transcription factors. One class of signalling molecules, retinoids, have been shown to be crucial for hindbrain patterning through direct trans-activation of Hox genes in the neuroectoderm.

Identification of hoxb1b downstream genes: hoxb1b as a regulatory factor controlling transcriptional networks and cell movement during zebrafish gastrulation.

Hox proteins are homeobox containing transcription factors that play important roles in patterning the presumptive central nervous system and the axial mesoderm in the early vertebrate embryo. Hox genes are first expressed during gastrula stages and recent studies suggest that their function goes beyond their role as patterning determinants. To improve our understanding of the role of Hox proteins during early vertebrate development, we designed a strategy to identify target genes of the zebrafish hoxb1b using overexpression and whole-genome microarray analysis.

Xwnt8 directly initiates expression of labial Hox genes.

Hox transcription factors play an essential role in patterning the anteroposterior axis during embryogenesis and exhibit a complex array of spatial and temporal patterns of expression. Their earliest onset of expression in vertebrates is during gastrulation in a temporally collinear sequence in the presomitic/ventrolateral mesoderm, and it is not clear which upstream signal transduction events initiate this expression. Using Xenopus, we present evidence that Xwnt8 is necessary for initiation of this collinear sequence by activating Hox-1 expression in three Hox clusters: hoxd, hoxa, and hoxb.

Axial patterning in snakes and caecilians: evidence for an alternative interpretation of the Hox code.

It is generally assumed that the characteristic deregionalized body plan of species with a snake-like morphology evolved through a corresponding homogenization of Hox gene expression domains along the primary axis. Here, we examine the expression of Hox genes in snake embryos and show that a collinear pattern of Hox expression is retained within the paraxial mesoderm of the trunk. Genes expressed at the anterior and most posterior, regionalized, parts of the skeleton correspond to the expected anatomical boundaries.

Two Hoxc6 transcripts are differentially expressed and regulate primary neurogenesis in Xenopus laevis.

Hox genes are key players in defining positional information along the main body axis of vertebrate embryos. In Xenopus laevis, Hoxc6 was the first homeobox gene isolated. It encodes two isoforms.

MiR-10 represses HoxB1a and HoxB3a in zebrafish.

Background: The Hox genes are involved in patterning the anterior-posterior axis. In addition to the protein coding Hox genes, the miR-10, miR-196 and miR-615 families of microRNA genes are conserved within the vertebrate Hox clusters. The members of the miR-10 family are located at positions associated with Hox-4 paralogues.

Comparative functional analysis provides evidence for a crucial role for the homeobox gene Nkx2.1/Titf-1 in forebrain evolution.

Knockout of the Nkx2.1 (Titf-1) homeobox gene in the mouse leads to severe malformation and size reduction of the basal telencephalon/preoptic area and basal hypothalamus, indicating an important role of this gene in forebrain patterning. Here we show that abrogation of the orthologous gene in the frog Xenopus laevis by way of morpholino knockdown also affects the relative size of major regions in both the telencephalon (subpallium versus pallium) and diencephalon (hypothalamus versus thalamus).

The role of the Spemann organizer in anterior-posterior patterning of the trunk.

The formation of the vertebrate body axis during gastrulation strongly depends on a dorsal signaling centre, the Spemann organizer as it is called in amphibians. This organizer affects embryonic development by self-differentiation, regulation of morphogenesis and secretion of inducing signals. Whereas many molecular signals and mechanisms of the organizer have been clarified, its function in anterior-posterior pattern formation remains unclear.

Extensive polycistronism and antisense transcription in the mammalian Hox clusters.

The Hox clusters play a crucial role in body patterning during animal development. They encode both Hox transcription factor and micro-RNA genes that are activated in a precise temporal and spatial sequence that follows their chromosomal order. These remarkable collinear properties confer functional unit status for Hox clusters.

Role of X-Delta-2 in the early neural development of Xenopus laevis.

The Drosophila Delta gene and its vertebrate homologues are ligands for the Notch receptor and are involved in a variety of developmental processes, including neurogenesis, boundary formation, and axon guidance. This study deals with the ectodermal expression and function of X-Delta-2 during early Xenopus laevis development. X-Delta-2 is expressed, from early neurula stages on, throughout the central nervous system (CNS; forebrain, eyes, midbrain, hindbrain, and spinal cord) and in the majority of the cranial placodes.