A question of homology for chordate adhesive organs

The larvae of aquatic vertebrates sometimes possess a transient, mucus-secreting gland on their heads. The most studied of these organs is the Xenopus cement gland. The tadpoles use it to attach to plants or to the water surface, supposedly to hide from predators and save energy before they can swim or feed. Moreover their gland, being innervated by trigeminal fibres, also mediates a locomotor stopping response when the larvae encounter an obstacle. We have described an equivalent organ on the head of the teleost Astyanax mexicanus, that we have called the casquette because of its shape and position on the larval head. The casquette is transient, sticky, secretes mucus, is innervated by the trigeminal ganglion, has an inhibitory function on larval swimming behavior, and expresses Bmp4 and Pitx1/2 during embryogenesis. Here we further discuss the nature of the equivalence between the frog cement gland and the fish casquette, and highlight the usefulness of non-conventional model species to decipher developmental and evolutionary mechanisms of morphological variations

Conservation, development, and function of a cement gland-like structure in the fish Astyanax mexicanus

The larvae of the fish Astyanax mexicanus transiently develop a flat and adhesive structure on the top of their heads that we have called “the casquette” (cas, meaning “hat”). We hypothesized that the cas may be a teleostean homolog of the well-studied Xenopus cement gland, despite their different positions and structures. Here we show that the cas has an ectodermal origin, secretes mucus, expresses bone morphogenic protein 4 (Bmp4) and pituitary homeobox 1/2 (Pitx1/2), is innervated by the trigeminal ganglion and serotonergic raphe neurons, and has a role in the control and the development of the larval swimming behavior. These developmental, connectivity, and behavioral functional data support a level of deep homology between the frog cement gland and the Astyanax cas and suggest that attachment organs can develop in varied positions on the head ectoderm by recruitment of a Bmp4-dependent developmental module. We also show that the attachment organs of the cichlid Tilapia mariae larvae display some of these features. We discuss the possibility that these highly diversified attachment glands may be ancestral to chordates and have been lost repetitively in many vertebrate classes

Competing signals drive telencephalon diversity

The telencephalon is the most complex brain region, controlling communication, emotion, movement and memory. Its adult derivatives develop from the dorsal pallium and ventral subpallium. Despite knowledge of genes required in these territories, we do not understand how evolution has shaped telencephalon diversity. Here, using rock- and sand-dwelling cichlid fishes from Lake Malawi, we demonstrate that differences in strength and timing of opposing Hedgehog and Wingless signals establish evolutionary divergence in dorsal-ventral telencephalon patterning. Rock dwellers exhibit early, extensive Hedgehog activity in the ventral forebrain resulting in expression of foxg1 before dorsal Wingless signals, and a larger subpallium. Sand dwellers show rapid deployment of Wingless, later foxg1 expression and a larger pallium. Manipulation of the Hedgehog and Wingless pathways in cichlid and zebrafish embryos is sufficient to mimic differences between rock- versus sand-dweller brains. Our data suggest that competing ventral Hedgehog and dorsal Wingless signals mediate evolutionary diversification of the telencephalon.</p

ESS Conceptual Design Report

The high intensity spallation neutron source ESS is well set to start construction in 2013 and to deliver �rst neutrons in 2019. The project itself has been 20 years in gestation but there has been a determination amongst the user community and those working in national and international neutron laboratories in Europe that it would be built. That determination is what has brought the project in where it is today. The baseline speci�cation is for a 5 MW power, long pulse facility delivering neutrons to 22 independent instruments for the study of materials in all their diversity from pharmaceuticals and membranes, to colloids and polymers, to magnetic and superconducting materials, and on to engineering and archeological artefacts. The user community is rich and equally diverse, containing approximately 6000 individuals according to �gures produced by ENSA, the European Neutron Scattering Association. This Conceptual Design Report represents the work of about 250 individual scientists and engineers around Europe and the rest of the world, with about 100 of them located in the central team in Lund in southern Scandinavia where the facility is to be built, with Sweden and Denmark as co-hosts. As this team has grown over the past 2 years, the work intensity and output has risen considerably. It has taken some time for the realisation that ESS is �nally to be built, to be fully digested, but it is clear now that this is indeed accepted. The CDR is a technical document. It does not address organisational matters, nor governance matters and less so �nancial matters, although it must be emphasised that these subjects are borne in mind in arriving at the scope of ESS and hence the speci�cation of the facility. Over the next 12 months, work will be engaged upon which will result in a Technical Design Report being produced together with a series of other documents such as an updated Costing Report. These documents will demonstrate the sound foundation upon which the project is to be constructed and are a necessary, but not su�cient, achievement to lead on seamlessly to construction. Su�ciency would require our 17 partner countries to reach a political and �nancial agreement. We are con�dent that it is within their capabilities and resources to do so, and we look to them for such a signal