Kumon, T. | Search bioRxiv

bioRxiv2020

Centromere drive and suppression by parallel pathways for recruiting microtubule destabilizers

Selfish centromere DNA sequences bias their transmission to the egg in female meiosis. Evolutionary theory suggests that centromere proteins evolve to suppress costs of this "centromere drive". In hybrid mouse models with genetically different maternal and paternal centromeres, selfish centromere DNA exploits a kinetochore pathway to recruit microtubule-destabilizing proteins that act as drive effectors. We show that such functional differences are suppressed by a parallel pathway for effector recruitment by heterochromatin, which is similar between centromeres in this system. Disrupting heterochromatin by CENP-B deletion amplifies functional differences between centromeres, whereas disrupting the kinetochore pathway with a divergent allele of CENP-C reduces the differences. Molecular evolution analyses using newly sequenced Murinae genomes identify adaptive evolution in proteins in both pathways. We propose that centromere proteins have recurrently evolved to minimize the kinetochore pathway, which is exploited by selfish DNA, relative to the heterochromatin pathway that equalizes centromeres, while maintaining essential functions.

evolutionary biology↗

bioRxiv2020

Mutually Beneficial Symbiosis Between Human and Gut-Dominant Bacteroides Species Through Bacterial Assimilation of Host Mucosubstances

The composition of gut microbiota is influenced by the quantity and type of nutrients in host. Even with some Bacteroides species being categorized as pathogens, Bacteroides is one of the most dominant gut bacteria. Here we indicate the physiological determinants of the species of Bacteroides for being dominant in human gut microbiota. Each of the host extracellular mucosubstances including glycosaminoglycans (GAGs) and mucin has grown human gut microbiota. In spite of the differences among initial microbiota profiles, Bacteroides species dominated the community when GAG (e.g., chondroitin sulfate or hyaluronan) was used as a sole carbon source. In fact, GAGs and the Bacteroides genes which are vital for the degradation of GAGs were commonly detected in human feces. Mucin has encouraged the growth of Bacteroides and several other genera. A comprehensive analysis on the degradation and assimilation of mucosubstances by the genus Bacteroides using around 30 species has shown that most species degrade and assimilate GAGs and mucin, showing that Bacteroides species can survive even in the undernutrition condition including the fasting state. In the assimilation of GAG or mucin, Bacteroides species significantly secreted essential amino acids, {gamma}-amino butyrate (GABA), and/or short-chain fatty acids which are needed for human health. This is the first report as regards mutually beneficial interaction between human and Bacteroides species via bacterial assimilation of host mucosubstances and secretion of metabolites for host health promotion. SignificanceThe genus Bacteroides is one of the most dominant gut bacteria, although its beneficial effects on human health have not been well understood. Here, we show modes of action in human-Bacteroides interrelationship. Mucosubstances including GAGs and mucin secreted by human host are abundant in gut for microbiota to grow well. Bacteroides species are dominant in the community in the presence of GAGs, and provide human host with a considerable amount of essential amino acids, {gamma}-amino butyrate, and short-chain fatty acids produced from mucosubstances. These results postulate mutually beneficial symbiosis system between human and Bacteroides through bacterial assimilation of host mucosubstances and secretion of metabolites for human body and mental health promotion even in the undernutrition condition including the fasting state.

microbiology↗