Caste development and reproduction: a genome-wide analysis of hallmarks of insect eusociality

The honey bee queen and worker castes are a model system for developmental plasticity. We used established expressed sequence tag information for a Gene Ontology based annotation of genes that are differentially expressed during caste development. Metabolic regulation emerged as a major theme, with a caste-specific difference in the expression of oxidoreductases vs. hydrolases. Motif searches in upstream regions revealed group-specific motifs, providing an entry point to cis-regulatory network studies on caste genes. For genes putatively involved in reproduction, meiosis-associated factors came out as highly conserved, whereas some determinants of embryonic axes either do not have clear orthologs (bag of marbles, gurken, torso), or appear to be lacking (trunk) in the bee genome. Our results are the outcome of a first genome-based initiative to provide an annotated framework for trends in gene regulation during female caste differentiation (representing developmental plasticity) and reproduction

Atlas-guided global tractography: imposing a prior on the local track orientation

Since its introduction over a decade ago, diffusion tractography has come a long way from local, deterministic methods, over probabilistic approaches, towards global tractography. Yet, the development of tractography methods has been largely focused on single subject data, and very little on cross-population analysis and inter-subject variability. In this work, we extend global tractography with a prior on the local track orientation distribution (TOD), derived from 20 normal subjects. The proposed method is evaluated in 5 independent subjects. Results show that adding such prior regularizes the reconstructed track distribution, although registration errors can induce local artefacts. We conclude that atlas-guided global tractography can improve the fibre reconstruction and ultimately detect and quantify inter-subject differences in tractography.status: publishe