Vertebrate myotome development

The embryonic myotome generates both the axial musculature and the appendicular muscle of the fins and limbs. Early in embryo development the mesoderm is segmented into somites, and within these the primary myotome forms by a complex series of cellular movements and migrations. A new model of primary myotome formation in amniotes has emerged recently. The myotome also includes the muscle progenitor cells that are known to contribute to the secondary formation of the myotome. The adult myotome contains satellite cells that play an important role in adult muscle regeneration. Recent studies have shed light on how the growth and patterning of the myotome occurs.     

Vertebrate eye development.

Vertebrate eye determination is mediated by a series of inductive interactions that have now been more precisely defined with the use of regional markers. Analyses of the genes responsible for eye mutations and the cloning of genes delimiting spatial domains within the developing eye have begun to elucidate the molecular basis of this process.     

Vertebrate development: taming the nodal waves

Recent results have provided evidence that regulatory loops operating in vertebrate embryos between the developmental signalling factors Nodal and Lefty may provide a real example of the kind of reaction-diffusion process long predicted to be a mechanism of pattern formation.     

Vertebrate development: wnt signals at the crest

Neural crest cells, a defining feature of vertebrate embryos, form at the neural plate border in response to inductive signals from the ectoderm. Recent studies have shown that Wnt signals are essential mediators of this induction.     

Vertebrate head development: Segmentation,novelties, and homology

Vertebrate head development is a classical topic lately invigorated by methodological as well as conceptual advances. In contrast to the classical segmentalist views going back to idealistic morphology, the head is now seen not as simply an extension of the trunk, but as a structure patterned by different mechanisms and tissues. Whereas the trunk paraxial mesoderm imposes its segmental pattern on adjacent tissues such as the neural crest derivatives, in the head the neural crest cells carry pattern information needed for proper morphogenesis of mesodermal derivatives, such as the cranial muscles. Neural crest cells make connective tissue components which attach the muscle fiber to the skeletal elements. These crest cells take their origin from the same visceral arch as the muscle cells, even when the skeletal elements to which the muscle attaches are from another arch. The neural crest itself receives important patterning influences from the pharyngeal endoderm. The origin of jaws can be seen as an exaptation in which a heterotopic shift of the expression domains of regulatory genes was a necessary step that enabled this key innovation. The jaws are patterned by Dlx genes expressed in a nested pattern along the proximo-distal axis, analogous to the anterior–posterior specification governed by Hox genes. Knocking out Dlx 5 and 6 transforms the lower jaw homeotically into an upper jaw. New data indicate that both upper and lower jaw cartilages are derived from one, common anlage traditionally labelled the “mandibular” condensation, and that the “maxillary” condensation gives rise to other structures such as the trabecula. We propose that the main contribution from evolutionary developmental biology to solving homology questions lies in deepening our biological understanding of characters and character states.     

Vertebrate development: the subtle art of germ-layer specification.

Nodal signalling is essential for vertebrate germ-layer formation. How this single signal can generate such a diverse array of tissues remains a mystery and is an area of intense research. Three recent reports reveal unanticipated subtleties to the process and provide new mechanisms for generating distinct responses.     

Vertebrate craniofacial development: novel approaches and new dilemmas.

Unexpected patterns of neuroblast, angioblast and myoblast movement and tissue organization have been defined using lineage tracing and transplantation methods. The most novel and enigmatic new data derive from analyses of genes in the Hox- and Pax-gene families. In addition to the characterization of expression patterns, the effects of Hox-gene knock-out and retinoic acid treatment have been assessed. These basic studies are complemented by the identification of correlations between inherited craniofacial anomalies, for example Waardenburg's syndrome, and the function of specific genes.     

Vertebrate limb development and possible clues to diversity in limb form

Chick embryos are good models for vertebrate development. The principles that underlie chick wing development have been discovered and there is increasing knowledge about the molecules involved. The importance of identifying molecules is that this provides a direct link to understanding the genetic basis of diversity in form. Chick wing development will be compared with limb development in other vertebrates. Possible mechanisms that could lead to variations in form, including limb reductions and limblessness, differences between fore- and hindlimbs, limb proportions, and interdigital webbing can be suggested.     

Vertebrate melanophores as potential model for drug discovery and development: A review

Drug discovery in skin pharmacotherapy is an enormous, continually expanding field. Researchers are developing novel and sensitive pharmaceutical products and drugs that target specific receptors to elicit concerted and appropriate responses. The pigment-bearing cells called melanophores have a significant contribution to make in this field. Melanophores, which contain the dark brown or black pigment melanin, constitute an important class of chromatophores. They are highly specialized in the bidirectional and coordinated translocation of pigment granules when given an appropriate stimulus. The pigment granules can be stimulated to undergo rapid dispersion throughout the melanophores, making the cell appear dark, or to aggregate at the center, making the cell appear light. The major signals involved in pigment transport within the melanophores are dependent on a special class of cell surface receptors called G-protein-coupled receptors (GPCRs). Many of these receptors of adrenaline, acetylcholine, histamine, serotonin, endothelin and melatonin have been found on melanophores. They are believed to have clinical relevance to skin-related ailments and therefore have become targets for high throughput screening projects. The selective screening of these receptors requires the recognition of particular ligands, agonists and antagonists and the characterization of their effects on pigment motility within the cells. The mechanism of skin pigmentation is incredibly intricate, but it would be a considerable step forward to unravel its underlying physiological mechanism. This would provide an experimental basis for new pharmacotherapies for dermatological anomalies. The discernible stimuli that can trigger a variety of intracellular signals affecting pigment granule movement primarily include neurotransmitters and hormones. This review focuses on the role of the hormone and neurotransmitter signals involved in pigment movement in terms of the pharmacology of the specific receptors.     

Vertebrate–arthropod communication dictates tick development and pathogen transmission

Cross-species communication drives the coordination of diverse biological processes in complex systems. Rana et al. discovered that Ixodes scapularis, the tick vector of Lyme disease, produces a receptor that binds host interferon-gamma (IFNγ) in the blood meal, which orchestrates tick development, immunity, and vector competence.     

Vertebrate evolution: turning heads

The skeleton of the neck and shoulders has undergone alterations during evolution, but muscle connectivity has not. A recent study suggests this is a result of neural crest cells defining attachment points and thus muscle connectivity.