By Any Other Name: Heterologous Replacement of the \u3ci\u3eEscherichia coli\u3c/i\u3e RNase P Protein Subunit Has \u3ci\u3eIn Vivo\u3c/i\u3e Fitness Consequences

Bacterial RNase P is an essential ribonucleoprotein composed of a catalytic RNA component (encoded by the rnpB gene) and an associated protein moiety (encoded by rnpA). We construct a system that allows for the deletion of the essential endogenous rnpA copy and for its simultaneous replacement by a heterologous version of the gene. Using growth rate as a proxy, we explore the effects on fitness of heterologous replacement by increasingly divergent versions of the RNase P protein. All of the heterologs tested complement the loss of the endogenous rnpA gene, suggesting that all existing bacterial versions of the rnpA sequence retain the elements required for functional interaction with the RNase P RNA. All replacements, however, exact a cost on organismal fitness, and particularly on the rate of growth acceleration, defined as the time required to reach maximal growth rate. Our data suggest that the similarity of the heterolog to the endogenous version — whether defined at the sequence, structure or codon usage level — does not predict the fitness costs of the replacement. The common assumption that sequence similarity predicts functional similarity requires experimental confirmation and may prove to be an oversimplification

Effects of oxytocin-family peptides and substance P on locomotor activity and filial preferences in visually naïve chicks.

Nonapeptides from the vasopressin/oxytocin family have been implicated in a wide variety of social behaviors across vertebrates. Experimental manipulations that alter nonapeptide levels or receptor function in the brain have provided evidence for understanding how nonapeptides influence responses to social stimuli in adults. While behaviors in adults have been extensively studied, much less in known about roles of nonapeptides in early life and the development of affiliative social behaviors. We examined an experience-independent preference (social predisposition) that is present at hatching and is characterized by the tendency of visually naïve chicks (Gallus gallus) to prefer to approach a stuffed-hen stimulus over a control stimulus in a choice test. Among chicks that show the social predisposition preference, bilateral intracranial mesotocin injections resulted in higher mean hen preference scores compared to saline-injected controls. Equimolar doses of mesotocin and vasotocin injections had different effects on locomotor activity: vasotocin, but not mesotocin, resulted in hypoactivity. We also tested whether intraperitoneal substance P had an effect on hen preference scores because previous research has proposed that vasotocin effects on social approach are mediated by peripheral release of substance P, but found no significant effect. All together, our data suggests that mesotocin signaling may be important for social predispositions and can potentially enhance the perceived salience of social stimuli soon after hatching. Specifically, mesotocin release and signaling in the brain may regulate the ability to recognize naturalistic stimuli and/or to act on the motivation to approach naturalistic stimuli

Increased glucocorticoid concentrations in early life cause mitochondrial inefficiency and short telomeres

Telomeres are DNA structures that protect chromosome ends. However, telomeres shorten during cell replication and at critically low lengths can reduce cell replicative potential, induce cell senescence and decrease fitness. Stress exposure, which elevates glucocorticoid hormone concentrations, can exacerbate telomere attrition. This phenomenon has been attributed to increased oxidative stress generated by glucocorticoids ('oxidative stress hypothesis'). We recently suggested that glucocorticoids could increase telomere attrition during stressful periods by reducing the resources available for telomere maintenance through changes in the metabolic machinery ('metabolic telomere attrition hypothesis'). Here, we tested whether experimental increases in glucocorticoid levels affected telomere length and mitochondrial function in wild great tit (Parus major) nestlings during the energy-demanding early growth period. We monitored resulting corticosterone (Cort) concentrations in plasma and red blood cells, telomere lengths and mitochondrial metabolism (metabolic rate, proton leak, oxidative phosphorylation, maximal mitochondrial capacity and mitochondrial inefficiency). We assessed oxidative damage caused by reactive oxygen species (ROS) metabolites as well as the total non-enzymatic antioxidant protection in plasma. Compared with control nestlings, Cort-nestlings had higher baseline corticosterone, shorter telomeres and higher mitochondrial metabolic rate. Importantly, Cort-nestlings showed increased mitochondrial proton leak, leading to a decreased ATP production efficiency. Treatment groups did not differ in oxidative damage or antioxidants. Hence, glucocorticoid-induced telomere attrition is associated with changes in mitochondrial metabolism, but not with ROS production. These findings support the hypothesis that shortening of telomere length during stressful periods is mediated by glucocorticoids through metabolic rearrangements

By Any Other Name: Heterologous Replacement of the Escherichia coli RNase P Protein Subunit Has In Vivo Fitness Consequences

Bacterial RNase P is an essential ribonucleoprotein composed of a catalytic RNA component (encoded by the rnpB gene) and an associated protein moiety (encoded by rnpA). We construct a system that allows for the deletion of the essential endogenous rnpA copy and for its simultaneous replacement by a heterologous version of the gene. Using growth rate as a proxy, we explore the effects on fitness of heterologous replacement by increasingly divergent versions of the RNase P protein. All of the heterologs tested complement the loss of the endogenous rnpA gene, suggesting that all existing bacterial versions of the rnpA sequence retain the elements required for functional interaction with the RNase P RNA. All replacements, however, exact a cost on organismal fitness, and particularly on the rate of growth acceleration, defined as the time required to reach maximal growth rate. Our data suggest that the similarity of the heterolog to the endogenous version — whether defined at the sequence, structure or codon usage level — does not predict the fitness costs of the replacement. The common assumption that sequence similarity predicts functional similarity requires experimental confirmation and may prove to be an oversimplification

Growth curves of test lineages.

<p>Growth curves for each of the test lineages averaged over >20 replicates (solid lines) are compared to the control lineage (5 replicates) (dashed lines). Control lineage curves represent the growth of <i>E. coli</i> MTea1 expressing the wild-type <i>rnpA</i> in pSWAP (MTea1/pSWAP-Ec). The test lineages depicted harbor the following heterologous <i>rnpA</i>s in an MTea1 background: A) <i>P. mirabilis</i> (Pm), B) <i>P. aeruginosa</i> (Pa), C) <i>A. baumannii</i> (Ab), D) <i>N. gonorrhoeae</i> (Ng), E) <i>T. maritima</i> (Tm), F) <i>S. aureus</i> (Sa), G) <i>B. subtilis</i> (Bs), H) <i>S. oralis</i> (So).</p

Average growth parameters (µmax and TTI) from growth curves.

a<p>Relative µmax means the ratio between the average µmax of each test lineage and the average µmax of the control lineage MTea1/pSWAP-Ec.</p>b<p>Relative TTI means the ratio between the average TTI of each test lineage and the average TTI of the control lineage MTea1/pSWAP-Ec.</p