Coordinate expression of the murine Hox-5 complex homoeobox-containing genes during limb pattern formation

Classic neontology (comparative embryology and anatomy), through the application of the concept of homology, has demonstrated that the development of the gnathostome (jawed vertebrate) skull is characterized both by a fidelity to the gnathostome bauplan and the exquisite elaboration of final structural design. Just as homology is an old concept amended for modern purposes, so are many of the questions regarding the development of the skull. With due deference to Geoffroy-St. Hilaire, Cuvier, Owen, Lankester et al., we are still asking: How are bauplan fidelity and elaboration of design maintained, coordinated, and modified to generate the amazing diversity seen in cranial morphologies? What establishes and maintains pattern in the skull? Are there universal developmental mechanisms underlying gnathostome autapomorphic structural traits? Can we detect and identify the etiologies of heterotopic (change in the topology of a developmental event), heterochronic (change in the timing of a developmental event), and heterofacient (change in the active capacetence, or the elaboration of capacity, of a developmental event) changes in craniofacial development within and between taxa? To address whether jaws are all made in a like manner (and if not, then how not), one needs a starting point for the sake of comparison. To this end, we present here a "hinge and caps" model that places the articulation, and subsequently the polarity and modularity, of the upper and lower jaws in the context of cranial neural crest competence to respond to positionally located epithelial signals. This model expands on an evolving model of polarity within the mandibular arch and seeks to explain a developmental patterning system that apparently keeps gnathostome jaws in functional registration yet tractable to potential changes in functional demands over time. It relies upon a system for the establishment of positional information where pattern and placement of the "hinge" is driven by factors common to the junction of the maxillary and mandibular branches of the first arch and of the "caps" by the signals emanating from the distal-most first arch midline and the lamboidal junction (where the maxillary branch meets the frontonasal processes). In this particular model, the functional registration of jaws is achieved by the integration of "hinge" and "caps" signaling, with the "caps" sharing at some critical level a developmental history that potentiates their own coordination. We examine the evidential foundation for this model in mice, examine the robustness with which it can be applied to other taxa, and examine potential proximate sources of the signaling centers. Lastly, as developmental biologists have long held that the anterior-most mesendoderm (anterior archenteron roof or prechordal plate) is in some way integral to the normal formation of the head, including the cranial skeletal midlines, we review evidence that the seminal patterning influences on the early anterior ectoderm extend well beyond the neural plate and are just as importan...

Section: Evidence Of Caps Signalsmentioning

confidence: 99%

21^st Century neontology and the comparative development of the vertebrate skull

Depew

Simpson

2006

“…4A,B; Tarchini and Duboule, 2006). The combination of these different phases results in an apparent (virtual) collinearity, giving rise to the posterodistal nested pattern that has been emblematic of Hoxd gene expression since the first analyses (Dolle et al, 1989). It also explains the complex evolution of this pattern with development (Nelson et al, 1996).…”

Section: Role Of Tbx Genes In Specification Of More Posterior Identitymentioning

confidence: 99%

Anteroposterior patterning in the limb and digit specification: Contribution of mouse genetics

Robert

Lallemand

2006

The limb has been a privileged object of investigation and reflection for scientists over the past two centuries and continues to provide a heuristic framework to analyze vertebrate development. Recently, accumulation of new data has significantly changed our view on the mechanisms of limb patterning, in particular along the anterior-posterior axis. These data have led us to revisit the mode of action of the zone of polarizing activity. They shed light on the molecular and cellular mechanisms of patterning linked to the Shh-Gli3 signaling pathway and give insights into the mechanism of activation of these cardinal factors, as well as the consequences of their activity. These new data are in good part the result of systematic Application of tools used in contemporary mouse molecular genetics. These have extended the power of mouse genetics by introducing mutational strategies that allow fine-tuned modulation of gene expression, interchromosomal deletions and duplication. They have even made the mouse embryo amenable to cell lineage analysis that used to be the realm of chick embryos. In this review, we focus on the data acquired over the last five years from the analysis of mouse limb development and discuss new perspectives opened by these results. Developmental Dynamics 235:2337-2352, 2006.

“…Members of the Hoxd (formerly Hox-4) complex are expressed in a diagonal, nested pattern from posteriordistal to anterior-proximal in the developing limb (Doll6 et al, 1989;Izpisua-Belmonte et al, 1991). Their expression is generally considered important in establishing anteroposterior positional identity (Tabin, 1992).…”

Section: Toward An Understanding Of Positional Differences In Limb-cementioning

confidence: 99%

Stage‐ and region‐dependent chondrogenesis and growth of chick wing‐bud mesenchyme in serum‐containing and defined tissue culture media

Paulsen

Chen

Pang

et al. 1994

During development, limb-bud mesenchymal cells carry out complex spatiotemporal patterns of growth and differentiation. Tissue and organ culture facilitate analysis of environmental influences on these cell behaviors, allowing their partial dissection into exogenous and endogenous components. Two factors that complicate such in vitro analyses are the heterogeneity of the cultured cells and imprecise knowledge of culture medium composition. Limb mesenchyme comprises a heterogenous cell population with important regional differences in cell type. Dividing the limb into subregions helps limit the cellular heterogeneity and using chemically defined, serum-free medium allays concerns about medium composition. In the present study, mesenchyme from different regions along the anteroposterior and proximodistal axes of stage 21-22 and stage 23-24 chick wing buds was grown in high-density microtiter cultures in chemically defined and in serum-containing medium. Fourday cultures of the various regions were compared in terms of culture morphology and the accumulation of Alcian blue-positive cartilage matrix and DNA. The results demonstrate stageand region-dependent differences in the in vitro growth, differentiation, and responsiveness of these cells. For example, mesenchyme from the distal anterior region of the wing bud exhibited lower intrinsic chondrogenic capacity and greater responsiveness to serum than other regions. Patterns of in vitro chondrogenesis also suggest that, at the stages examined, distal wing-bud mesenchyme may be less homogeneous than has been believed. A case is made for the suitability of serum-free medium for future in vitro studies of chick limb-bud mesenchyme. The results are considered in relation to the process of limb development and regional expression of pattern-related genes. 0 1994 Wiley-Liss, Inc.