Myoglobin primary structure reveals multiple convergent transitions to semi-aquatic life in the world's smallest mammalian divers

Abstract

Working memory (WM), the ability to actively hold information in memory over a delay period of seconds, is a fundamental constituent of cognition. Delay-period activity in sensory cortices has been observed in WM tasks, but whether and when the activity plays a functional role for memory maintenance remains unclear. Here, we investigated the causal role of auditory cortex (AC) for memory maintenance in mice performing an auditory WM task. Electrophysiological recordings revealed that AC neurons were active not only during the presentation of the auditory stimulus but also early in the delay period. Furthermore, optogenetic suppression of neural activity in AC during the stimulus epoch and early delay period impaired WM performance, whereas suppression later in the delay period did not. Thus, AC is essential for information encoding and maintenance in auditory WM task, especially during the early delay period.

Mitogenome and phylogenetic analyses support rapid diversification among species groups of small-eared shrews genus <i>Cryptotis</i> (Mammalia: Eulipotyphla: Soricidae)

“…Cryptotis gracilis was previously embedded in the C. goldmani -group but only supported by Bayesian analysis, which can be overestimated ( Baird et al, 2018 ; He et al, 2015 ). We also observed several unresolved relationships: (i) the sister relationship of Soricini and Nectogalini+Anourosoricini in our outgroups was moderately supported, although this was not unexpected ( see He et al, 2021 ); (ii) the relationships among Nectogalini water shrews were not resolved as observed by He et al ( 2010 ); and (iii) within Cryptotis , the phylogenetic positions of two species, C. mexicanus and C. goldmani , were not resolved (BS<56, PP<0.94).…”

Common and unique strategies of myoglobin evolution for deep-sea adaptation of diving mammals

“…The major strategies for the diving adaptation of Mbs revealed in this and previous studies are schematically summarized in Figure 9 ( Dasmeh et al., 2013 ; He et al., 2021 ; Isogai et al., 2018 ; Mirceta et al., 2013 ). In conclusion, a total of 18 residues were replaced on or near the protein surface of Mb, during the pinniped evolution from the terrestrial ancestor to the deep-diving extant seal.…”

“…A substitution of flexible surface amino acid, such as arginine, into smaller one, typically alanine, is one of the efficient strategies to induce protein crystallization (precipitation), known as the surface entropy reduction ( Cooper et al., 2007 ; Derewenda, 2004 ; Derewenda and Vekilov, 2006 ). The amino acid substitutions in the opposite direction observed in the diving adaptation of Mbs are thought to suppress protein precipitation ( He et al., 2021 ; Romero-Herrera et al., 1978 ). The d E eff /d R g decrease implies a wider conformational space around the native structure, within which conformational flexibility is expected to be high.…”

Dive Performance and Aquatic Thermoregulation of the World’s Smallest Mammalian Diver, the American Water Shrew (Sorex palustris)

“…Nonetheless, skeletal muscle myoglobin concentrations of adult water shrews are 2–4× those of strictly terrestrial short-tailed (0.16 to 0.30 g 100 g −1 ; Stewart et al 2005 and Table 3) and Etruscan shrews, Suncus etruscus (0.15 g 100 g −1 ; Jürgens 2002), suggesting an adaptive increase associated with diving. This difference appears to be linked to the marked increase in the net surface charge of S. palustris myoglobin versus those of non-diving shrews, which is proposed to foster higher myoglobin concentrations by minimizing the potential for newly synthesized (apomyoglobin) and mature protein chains from aggregating/precipitating (Mirceta et al 2013; Samuel et al 2015; He et al 2021). Of note, the highest myoglobin concentrations were found in the heart for both short-tailed (0.88 g 100 g −1 ) and water shrews (1.10 g 100 g −1 ).…”