The behavioural and physiological stress responses are linked to plumage coloration in the rock pigeon (Columbia livia).

In wild vertebrates, conspicuousness often signals a high phenotypic quality and is therefore associated with fitness benefits ("the handicap principle hypothesis"). However, conspicuous individuals usually face a higher risk of predation because they are easier to detect. Therefore, conspicuous individuals are expected to modify their behavioural and their physiological stress responses to limit the negative effect of their conspicuousness on survival. We examined the link between plumage coloration and the stress response in a bird species (the rock pigeon, Columbia livia) by comparing two groups of pigeons with different plumage characteristics: 'blue-bar' birds (lighter birds) and 'checker' birds (darker birds). Specifically, we measured several behavioural and physiological components of the stress response (breath rate, corticosterone, and tonic immobility). Although breath rate did not differ between 'checker' and 'blue bar' birds, the corticosterone stress response of 'blue-bar' birds was greater relative to that of 'checker' birds. Moreover, 'checker' birds were more likely to initiate tonic immobility relative to 'blue bar' birds. Therefore, this study suggests that the behavioural and physiological stress responses of wild birds may differ according to their plumage coloration. To conclude, our results suggest that plumage colorations may be functionally linked to specific behavioural and physiological sensitivities to stressors.

Endocrine consequences of an acute stress under different thermal conditions: A study of corticosterone, prolactin, and thyroid hormones in the pigeon (Columbia livia).

In the context of global change, the physiological and hormonal stress responses have received much attention because of their implications in terms of allostasis. However, most studies have focused on glucocorticoids only as the "common" response to stressors while neglecting other endocrine axes and hormones (e.g. prolactin, thyroid hormones) that play a crucial role in metabolic adjustments. Interestingly, the responsiveness of all these endocrine axes to stress may depend on the energetic context and this context-dependent stress response has been overlooked so far. In the wild, temperature can vary to a large extent within a short time window and ambient temperature may affect these metabolic-related endocrine axes, and potentially, their responsiveness to an acute stressor. Here, we explicitly tested this hypothesis by examining the effect of a standardized stress protocol on multiple hormonal responses in the rock pigeon (Columbia livia). We tested the effect of an acute restraint stress on (1) corticosterone levels, (2) prolactin levels, and (3) thyroid hormone levels (triiodothyronine, thyroxine) in pigeons that were held either at cool temperature (experimental birds) or at room temperature (control birds) during the stress protocol. Although we found a significant influence of restraint stress on most hormone levels (corticosterone, prolactin, and thyroxine), triiodothyronine levels were not affected by the restraint stress. This demonstrates that stressors can have significant impact on multiple endocrine mechanisms. Importantly, all of these hormonal responses to stress were not affected by temperature, demonstrating that the exposure to cold temperature does not affect the way these hormone levels change in response to handling stress. This suggests that some endocrine responses to temperature decreases may be overridden by the endocrine responses to an acute restraint stress.

Does the stress response predict the ability of wild birds to adjust to short-term captivity? A study of the rock pigeon (Columbia livia).

Although the transfer of wild animals to captivity is crucial for conservation purposes, this process is often challenging because some species or individuals do not adjust well to captive conditions. Chronic stress has been identified as a major concern for animals held on long-term captivity. Surprisingly, the first hours or days of captivity have been relatively overlooked. However, they are certainly very stressful, because individuals are being transferred to a totally novel and confined environment. To ensure the success of conservation programmes, it appears crucial to better understand the proximate causes of interspecific and interindividual variability in the sensitivity to these first hours of captivity. In that respect, the study of stress hormones is relevant, because the hormonal stress response may help to assess whether specific individuals or species adjust, or not, to such captive conditions ('the stress response-adjustment to captivity hypothesis'). We tested this hypothesis in rock pigeons by measuring their corticosterone stress response and their ability to adjust to short-term captivity (body mass loss and circulating corticosterone levels after a day of captivity). We showed that an increased corticosterone stress response is associated with a lower ability to adjust to short-term captivity (i.e. higher body mass loss and circulating corticosterone levels). Our study suggests, therefore, that a low physiological sensitivity to stress may be beneficial for adjusting to captivity. Future studies should now explore whether the stress response can be useful to predict the ability of individuals from different populations or species to not only adjust to short-term but also long-term captivity.

Time-lapse microscopy and fluorescence resonance energy transfer to analyze the dynamics and interactions of nucleolar proteins in living cells.

The dynamics of proteins play a key role in the organization and control of nuclear functions. Techniques were developed recently to observe the movement and interactions of proteins in living cells; time-lapse microscopy using fluorescent-tagged proteins gives access to observations of nuclear protein trafficking over time, and fluorescence resonance energy transfer (FRET) is used to investigate protein interactions in the time-lapse mode. In this chapter, we describe the application of these two approaches to follow the recruitment of nucleolar processing proteins at the time of nucleolar assembly. We question the role of prenucleolar bodies (PNB) during migration of the processing proteins from the chromosome periphery to sites of ribosomal genes (rDNA) transcription. The order of recruitment of different processing proteins into nucleoli is the consequence of differential sorting from the same PNBs. The dynamics of the interactions between processing proteins in PNBs suggest that PNBs are preassembly platforms for ribosomal RNA (rRNA) processing complexes.

Tracking the interactions of rRNA processing proteins during nucleolar assembly in living cells.

Reorganization of the nuclear machinery after mitosis is a fundamental but poorly understood process. Here, we investigate the recruitment of the nucleolar processing proteins in the nucleolus of living cells at the time of nucleus formation. We question the role of the prenucleolar bodies (PNBs), during migration of the processing proteins from the chromosome periphery to sites of rDNA transcription. Surprisingly, early and late processing proteins pass through the same PNBs as demonstrated by rapid two-color four-dimensional imaging and quantification, whereas a different order of processing protein recruitment into nucleoli is supported by differential sorting. Protein interactions along the recruitment pathway were investigated using a promising time-lapse analysis of fluorescence resonance energy transfer. For the first time, it was possible to detect in living cells the interactions between proteins of the same rRNA processing machinery in nucleoli. Interestingly interactions between such proteins also occur in PNBs but not at the chromosome periphery. The dynamics of these interactions suggests that PNBs are preassembly platforms for rRNA processing complexes.

Xenopus single-minded (xSim) is a nuclear factor allowing nuclear translocation of its cytoplasmic partner xArnt.

Transcription factors belonging to the basic helix-loop-helix Per-Arnt-Sim (bHLH/PAS) family control a wide variety of biological processes in mammalian and/or Drosophila. We have previously isolated bHLH/PAS Xenopus amphibian homologs of Single-minded (xSim) and aryl receptor nuclear translocator (xArnt) and characterized their expression pattern during embryogenesis. We show in this paper that xSim protein is a functional homolog of Drosophila or mammalian Sim(s). Biochemical analysis indicates that xSim forms a heterodimer with xArnt. Subcellular localization analysis of bHLH/PAS chimeric fluorescent versions in Xenopus or mammalian cell lines shows that xSim is constitutively localized in the nuclear compartment. On the opposite, xArnt appears to be predominantly expressed in the cytoplasm. In addition, we demonstrate that xArnt nuclear localization depends on the presence of xSim. Thus xSim appears to be an essential factor in the nuclear translocation of the xSim/xArnt complex. In perfect agreement, we show that the C-terminal half of xSim contains the information for this nuclear localization.

Relocalization of an 82-kDa protein from lampbrush loops into the nucleoskeleton during amphibian oogenesis.

Affinity-purified antibodies directed against an 82-kDa oocyte nuclear protein ofPleurodeles waltl (Amphibia, Urodela) were prepared using antigen bound to nitrocellulose paper. The specificity of the antibody was controlled on two-dimensional electrophoretic gels of nuclear proteins. The intranuclear distribution of the 82-kDa protein was analyzed by the indirect immunofluorescence method on spreads of oocyte nuclear content. Localization of the protein appeared to be extremely variable. The antibody recognized the protein (a) on normal and landmark loop matrices (but not simultaneously), (b) on ribonucleoprotein particles associated (or not) with the nucleoskeleton and (c) on nucleoli. This suggests the intervention of the protein at a certain physiological moment in the transcriptional or posttranscriptional process.