Nest box entrance hole size can influence nest site selection and nest defence behaviour in Japanese tits.

Birds have the ability to assess the risk of predation in their environment and adjust their antipredation strategies based on this risk information. However, whether nest site selection has effect on subsequent nest defence behaviour has not been studied. In this study, we aimed to determine whether the Japanese tit (Parus minor) exhibits a nest-box hole size preference and whether the entrance hole sizes of nest boxes influence the nest defence behaviour of tits. We hung nest boxes with three different entrance hole sizes (diameters: 6.5 cm, 4.5 cm and 2.8 cm) in our study sites and investigated which nest boxes were occupied by tits. In addition, by using dummy-presentation experiments, we observed the nest defence behaviours of tits that nested in boxes with 2.8 cm and 4.5 cm entrance holes towards common chipmunks (Tamias sibiricus, a small nest predator able to enter these holes) and Eurasian red squirrels (Sciurus vulgaris, a large nest predator unable to enter the 2.8 cm entrance hole). The tits that bred in nest boxes with 2.8 cm entrance holes exhibited more intense nest defence responses to chipmunks than to squirrels. In contrast, the tits that bred in nest boxes with 4.5 cm entrance holes exhibited similar nest defence responses to chipmunks and squirrels. Additionally, Japanese tits that bred in nest boxes with 2.8 cm entrance holes exhibited more intense behavioural responses to chipmunks than those that bred in nest boxes with 4.5 cm entrance holes. Our results suggested that Japanese tits prefer to occupy nest boxes with small holes for breeding and that nest-box characteristics influenced their nest defence behaviour.

Removing the regulatory N-terminal domain of cardiac troponin I diminishes incompatibility during bacterial expression.

Troponin I (TnI) is a muscle-specific protein and plays an allosteric function in the Ca(2+) regulation of cardiac and skeletal muscle contraction. Expression of cloned cDNA in Escherichia coli is an essential approach to preparing human TnI and mutants for structural and functional studies. The expression level of cardiac TnI in E. coli is very low. To reduce the potential toxicity of cardiac TnI to the host cell, we constructed a bi-cistronic expression vector to co-express cardiac TnI and cardiac/slow troponin C (TnC), a natural binding partner of TnI and a protein that readily expresses in E. coli at high levels. The co-expression moderately increased the expression of cardiac TnI although a high amount of TnC protein was produced from the bi-cistronic mRNA. The use of an E. coli strain containing additional tRNAs for certain low bacterial usage eukaryotic codons improved the expression of cardiac TnI. Modifications of two 5'-regional codons that have predicted low usages in bacterial cells did not reproduce the improvement, indicating that not the 5' but the overall codon usage restricts the translational efficiency of cardiac TnI mRNA in E. coli. However, deletion of the cardiac TnI-specific N-terminal 28 amino acids significantly improved the protein expression independent of the host cell tRNA modifications. The results suggest that the regulatory N-terminal domain of cardiac TnI is a dominant factor for the incompatibility in bacterial cells, supporting its role in modulating the overall molecular conformation.

Muscularizing tissues in the endocardial cushions of the avian heart are characterized by the expression of h1-calponin.

Muscularization of mesenchymal tissues in the developing heart is an important event in the morphogenesis of the valvuloseptal complex in four-chambered hearts. Perturbation of muscularization has been implicated in the pathogenesis of cardiac malformations in several animal models for congenital heart disease, including the Trisomy 16 mouse and the TGFbeta2 knockout mouse. Studies to unravel the mechanism of muscularization, as well as studies to determine the extent of the process in frequently used animal-model systems for cardiac development, have, thus far, been hampered by the lack of useful differentiation markers for muscularizing tissues, albeit that it had been demonstrated that, in the mouse, muscularizing cells are characterized by an elevated level of smooth muscle actin expression. In this study, we investigated whether muscularization of endocardial cushions in the avian heart is also accompanied by the expression of smooth muscle cell markers. The results presented in this study demonstrate that, in quail and chick, a specific population of muscularizing cells is recognized by the expression of smooth muscle h1-calponin. Interestingly, other genes typically found in smooth muscle cells (e.g., smooth muscle actin and caldesmon) are not expressed in muscularizing tissues. We conclude that muscularization of cushion-derived mesenchymal tissues is associated with a discrete genetic program reflected by the expression of h1-calponin and predict that h1-calponin will prove an invaluable tool in elucidating the regulation of muscularization and other aspects related to this event.