Spatial and temporal expression of the retinoic acid receptor in the regenerating amphibian limb

Retinoic acid is known to have dramatic effects on vertebrate limb pattern in development and regeneration, supporting a model in which a gradient of retinoic acid serves as a morphogen to differentially supply positional information to a developing limb. The discovery of a retinoic acid receptor (RAR) and its homology to the steroid and thyroid hormone receptors provided a potential molecular mechanism for limb morphogenesis. One prediction of this model is that the receptor must be expressed in the developing and regenerating limb anlage. We investigated the expression of the RAR in the adult newt, Notophthalmus viridescens, whose amputated limbs are capable of regenerating and upon which retinoic acid can act to alter pattern. We report the cloning of cDNAs encoding a functional newt RAR and the localization of high and uniform levels of RAR mRNA specifically in the regenerating cells that control limb pattern. These results indicate that the morphogenic field is established through differential activation of pre-existing retinoic acid receptors rather than differential expression of the RAR gene.     

Trading zones and interactional expertise

The phrase ‘trading zone’ is often used to denote any kind of interdisciplinary partnership in which two or more perspectives are combined and a new, shared language develops. In this paper we distinguish between different types of trading zone by asking whether the collaboration is co-operative or coerced and whether the end-state is a heterogeneous or homogeneous culture. In so doing, we find that the voluntary development of a new language community—what we call an inter-language trading zone—represents only one of four possible configurations. In developing this argument we show how different modes of collaboration result in different kinds of trading zone, how different kinds of trading zone may be ‘nested’ inside each other and discuss how a single collaboration might move between different kinds of trading zone over time. One implication of our analysis is that interactional expertise is a central component of at least one class of trading zone.     

Experiments with interactional expertise

‘Interactional expertise’ is developed through linguistic interaction without full scale practical immersion in a culture. Interactional expertise is the medium of communication in peer review in science, in review committees, and in interdisciplinary projects. It is also the medium of specialist journalists and of interpretative methods in the social sciences. We describe imitation game experiments designed to make concrete the idea of interactional expertise. The experiments show that the linguistic performance of those well socialized in the language of a specialist group is indistinguishable from those with full blown practical socialization but distinguishable from those who are not well socialized. The imitation game can also be used to indicate whether an individual can enter an esoteric domain and master the interactional expertise, a skill required by interpretative sociologists of science, anthropologists, ethnographers, and the like.     

Checklist of the Odonata of Colorado

One hundred and one species of Odonata are recorded for Colorado, including 58 species of Anisoptera (of which 4 are new state records) and 43 Zygoptera (9 new state records). County records are indicated for each. Three major elements are recognized; predominantly eastern species occurring in the plains and mountain valleys east of the Rocky Mountains, Canadian Zone elements occurring principally above 2,440 m (8,000 ft) in the mountains, and Great Basin and western species occurring chiefly west of the mountains. The list is based primarily on the collections at Colorado State University and the University of Colorado, with additional records from the literature and from other collections.     

Expertise revisited,Part I—Interactional expertise

In Part I of this two part paper we try to set out the ‘essence’ of the notion of interactional expertise by starting with its origins. In Part II we will look at the notion of contributory expertise. The exercise has been triggered by recent discussion of these concepts in this journal by Plaisance and Kennedy and by Goddiksen.     

Selective antagonism by Mg2+ of amino acid-induced depolarization of spinal neurones.

In the isolated frog or rat spinal cord, low concentrations of Mg2+ (0.5-1.00 mM) markedly depress, in a substantially Ca2+-independent manner, ventral root depolarizations produced by dorsal root stimulation and by certain amino acids (e.g. N-methyl-D-aspartate and L-homocysteate) but do not depress depolarizations produced by other excitatory amino acids (e.g. kainate and quisqualate). L-Aspartate-induced depolarizations are more sensitive to Mg2+ then are L-glutamate-induced depolarizations.     

澳大利亚麦龙虾触角腺组织学的初步研究

本文首次报道了以组织学手段对澳大利亚淡水螯虾-麦龙虾的触角腺进行研究的结果。根据组织学(?)征麦龙虾的触角腺可分为三个部分,它们依次为:端囊,迷路和肾管。端囊部分的细胞呈柱状,细胞核位于基部或中部。迷路部分的细胞呈短柱状,顶端有刷状缘,核位于基部或亚中部。肾管部分的细胞扁平,核很大偏向顶端,占据了细胞的大部分空间。在迷路和肾管部分没有明显的亚区的分别。