The anatomy of mole locomotion

The main features of the limb anatomy of the mole (Talpa europaea L.) are described and illustrated, following, but simplifying, Reed's (1951) account. The importance of the axial rotation of the humerus, shown in his account, is emphasized and also illustrated. Additional details of the structure and mode of action of the wrist are given.     

The anatomy of meaning and syntax

Recent brain imaging studies have provided evidence that distinct parts of the left frontal cortex are involved in processing the structure (syntax) and meaning (semantics) of a sentence, setting the stage for the development of more precise neuroanatomical models of language processing.     

The algorithmic anatomy of model-based evaluation

Despite many debates in the first half of the twentieth century, it is now largely a truism that humans and other animals build models of their environments and use them for prediction and control. However, model-based (MB) reasoning presents severe computational challenges. Alternative, computationally simpler, model-free (MF) schemes have been suggested in the reinforcement learning literature, and have afforded influential accounts of behavioural and neural data. Here, we study the realization of MB calculations, and the ways that this might be woven together with MF values and evaluation methods. There are as yet mostly only hints in the literature as to the resulting tapestry, so we offer more preview than review.     

The anatomy of protein beta-sheet topology

Here, we present a systematic analysis of the open-faced beta-sheet topologies in a set of non-redundant protein domain structures; in particular, we focus on the topological diversity of four-stranded beta-sheet motifs. Of the 96 topologies that are possible for a four-stranded beta-sheet, 42 were identified in known protein structures. Of these, four account for 50% of the structures that we have studied. Two sets of the topologies that were not observed may represent the section of the topological space that is not readily accessible to proteins on either thermodynamic or kinetic grounds. The first set contains topologies with alternating parallel and antiparallel beta-ladders. Their rare occurrence reflects the expectation that it is energetically unfavorable to match different hydrogen bonding patterns. The polypeptide chains in the second set of topologies go through convoluted paths and are expected to experience great kinetic frustrations during the folding processes. A knowledge of the potential causes for the topological preference of small beta-sheets also helps us to understand the topological properties of larger beta-sheet structures which frequently contain four-stranded motifs. The notion that protein topologies can only be taken from a confined and discrete space has important implications for structural genomics.     

The regulatory anatomy of honeybee lifespan

Honeybee workers (Apis mellifera) may be classified as either short-lived summer bees or long-lived winter bees in temperate zones. The protein status appears to be a major determinant of honeybee lifespan, and the lipoprotein vitellogenin seems to play a crucial role. Here, we give a review of the role of the vitellogenin in honeybee workers, and present a data-driven mathematical model describing the dynamics of this representative protein in the individual bee as a function of its task profile under various regimes. The results support the hypothesis that vitellogenin is a true storage protein that is utilized for various metabolic purposes including the synthesis of brood food. Except for workers having been foragers for many days, they also suggest that the previous life histories of workers do not constrain them from becoming winter bees as long as they get ample food and time to build up their protein reserves before wintering. The results also indicate that it may not be necessary to introduce the ovary as a storage organ for vitellogenin in order to generate normal winter bees. The insights gained from these results are then discussed in a broader gerontological and life history context. Remarkably similar features concerning regulation of ageing in Caenorhabditis elegans, Drosophila melanogaster and honeybees are pointed out and discussed. Furthermore, we show that in contrast to the "mutation accumulation" and the "antagonistic pleiotropy" evolutionary theories of ageing, the "disposable soma" theory is capable of explaining the bimodal longevity distribution of honeybees when interpreted in a group selection context. Finally, by showing that depletion of nutrient stores can be actively controlled by pathways connected to regulation of ageing, we strengthen the claim that age-based division of labour, with performance of risky tasks delayed until late in life by workers with depleted nutrient stores, may have evolved as an energy-saving mechanism in insect colonies.     

The locomotor anatomy of Australopithecus afarensis

The postcranial skeleton of Australopithecus afarensis from the Hadar Formation, Ethiopia, and the footprints from the Laetoli Beds of northern Tanzania, are analyzed with the goal of determining (1) the extent to which this ancient hominid practiced forms of locomotion other than terrestrial bipedality, and (2) whether or not the terrestrial bipedalism of A. afarensis was notably different from that of modern humans. It is demonstrated that A. afarensis possessed anatomic characteristics that indicate a significant adaptation for movement in the trees. Other structural features point to a mode of terrestrial bipedality that involved less extension at the hip and knee than occurs in modern humans, and only limited transfer of weight onto the medial part of the ball of the foot, but such conclusions remain more tentative than that asserting substantive arboreality. A comparison of the specimens representing smaller individuals, presumably female, to those of larger individuals, presumably male, suggests sexual differences in locomotor behavior linked to marked size dimorphism. The males were probably less arboreal and engaged more frequently in terrestrial bipedalism. In our opinion, A. afarensis from Hadar is very close to what can be called a "missing link." We speculate that earlier representatives of the A. afarensis lineage will present not a combination of arboreal and bipedal traits, but rather the anatomy of a generalized ape.     

The recombinational anatomy of a mouse chromosome

Among mammals, genetic recombination occurs at highly delimited sites known as recombination hotspots. They are typically 1-2 kb long and vary as much as a 1,000-fold or more in recombination activity. Although much is known about the molecular details of the recombination process itself, the factors determining the location and relative activity of hotspots are poorly understood. To further our understanding, we have collected and mapped the locations of 5,472 crossover events along mouse Chromosome 1 arising in 6,028 meioses of male and female reciprocal F1 hybrids of C57BL/6J and CAST/EiJ mice. Crossovers were mapped to a minimum resolution of 225 kb, and those in the telomere-proximal 24.7 Mb were further mapped to resolve individual hotspots. Recombination rates were evolutionarily conserved on a regional scale, but not at the local level. There was a clear negative-exponential relationship between the relative activity and abundance of hotspot activity classes, such that a small number of the most active hotspots account for the majority of recombination. Females had 1.2x higher overall recombination than males did, although the sex ratio showed considerable regional variation. Locally, entirely sex-specific hotspots were rare. The initiation of recombination at the most active hotspot was regulated independently on the two parental chromatids, and analysis of reciprocal crosses indicated that parental imprinting has subtle effects on recombination rates. It appears that the regulation of mammalian recombination is a complex, dynamic process involving multiple factors reflecting species, sex, individual variation within species, and the properties of individual hotspots.     

The biochemical anatomy of cortical inhibitory synapses

Classical electron microscopic studies of the mammalian brain revealed two major classes of synapses, distinguished by the presence of a large postsynaptic density (PSD) exclusively at type 1, excitatory synapses. Biochemical studies of the PSD have established the paradigm of the synapse as a complex signal-processing machine that controls synaptic plasticity. We report here the results of a proteomic analysis of type 2, inhibitory synaptic complexes isolated by affinity purification from the cerebral cortex. We show that these synaptic complexes contain a variety of neurotransmitter receptors, neural cell-scaffolding and adhesion molecules, but that they are entirely lacking in cell signaling proteins. This fundamental distinction between the functions of type 1 and type 2 synapses in the nervous system has far reaching implications for models of synaptic plasticity, rapid adaptations in neural circuits, and homeostatic mechanisms controlling the balance of excitation and inhibition in the mature brain.