‘Dunbar's number’ deconstructed

A widespread and popular belief posits that humans possess a cognitive capacity that is limited to keeping track of and maintaining stable relationships with approximately 150 people. This influential number, ‘Dunbar''s number’, originates from an extrapolation of a regression line describing the relationship between relative neocortex size and group size in primates. Here, we test if there is statistical support for this idea. Our analyses on complementary datasets using different methods yield wildly different numbers. Bayesian and generalized least-squares phylogenetic methods generate approximations of average group sizes between 69–109 and 16–42, respectively. However, enormous 95% confidence intervals (4–520 and 2–336, respectively) imply that specifying any one number is futile. A cognitive limit on human group size cannot be derived in this manner.     

Multiple α-Glucoside Transporter Genes in Brewer’s Yeast

Maltose and maltotriose are the two most abundant fermentable sugars in brewer’s wort, and the rate of uptake of these sugars by brewer’s yeast can have a major impact on fermentation performance. In spite of this, no information is currently available on the genetics of maltose and maltotriose uptake in brewing strains of yeast. In this work, we studied 30 brewing strains of yeast (5 ale strains and 25 lager strains) with the aim of examining the alleles of maltose and maltotriose transporter genes contained by them. To do this, we hybridized gene probes to chromosome blots. Studies performed with laboratory strains have shown that maltose utilization is conferred by any one of five unlinked but highly homologous MAL loci (MAL1 to MAL4 and MAL6). Gene 1 at each locus encodes a maltose transporter. All of the strains of brewer’s yeast examined except two were found to contain MAL11 and MAL31 sequences, and only one of these strains lacked MAL41. MAL21 was not present in the five ale strains and 12 of the lager strains. MAL61 was not found in any of the yeast strains. In three of the lager strains, there was evidence that MAL transporter gene sequences occurred on chromosomes other than those known to carry MAL loci. Sequences corresponding to the AGT1 gene, which encodes a transporter of several α-glucosides, including maltose and maltotriose, were detected in all but one of the yeast strains. Homologues of AGT1 were identified in three of the lager strains, and two of these homologues were mapped, one to chromosome II and the other to chromosome XI. AGT1 appears to be a member of a family of closely related genes, which may have arisen in brewer’s yeast in response to selective pressure.     

Mechanotransduction by Membrane Proteins: Worms find PEZO-1’s function easy to swallow

JGP study finds that the C. elegans orthologue of the PIEZO family is a mechanosensitive ion channel that regulates pharyngeal pumping and food sensation.

The PIEZO family of mechanosensitive cation channels has been implicated in a wide variety of physiological processes in mammals and is also associated with human disease. Mammalian genomes encode two family members, known as Piezo1 and Piezo2, but invertebrates such as the nematode Caenorhabditis elegans only possess a single Piezo-related gene (1). The function of the C. elegans orthologue, known as pezo-1, has largely remained obscure, but, in this issue of JGP, Millet et al. reveal that it encodes a bona fide mechanosensitive ion channel that regulates pharyngeal activity (2).Jonathan Millet (left), Valeria Vásquez (center), and colleagues reveal that pezo-1, the sole PIEZO family member in C. elegans, is a mechanosensitive ion channel that regulates pharyngeal pumping and food sensation, particularly when worms are fed with large and stiff bacterial filaments that are difficult to swallow (graphic created with BioRender.com).In 2020, an elegant study demonstrated that pezo-1 controls C. elegans ovulation and fertilization (3). However, explains Valeria Vásquez from the University of Tennessee Health Science Center, whether pezo-1 encodes for a mechanosensitive ion channel was unknown. “PEZO-1 is expressed in many tissues, including the pharynx, which is the organ we decided to concentrate on in our study,” Vásquez says.Muscle cells in the C. elegans pharynx rhythmically contract and relax to pump food into the worm’s intestine. Vásquez and colleagues, including first author Jonathan Millet, found that PEZO-1 is expressed in several different pharyngeal cell types (2), including the gland cells whose secretions lubricate the pharynx, and the proprioceptive NSM neurons that are thought to sense the presence of food within the pharynx lumen and release serotonin to increase the rate of pharyngeal pumping.Millet et al. analyzed pharyngeal pumping in worms lacking pezo-1, as well as in animals expressing a pezo-1 point mutant that, in human Piezo1, increases channel function by slowing channel deactivation and inactivation. Loss or gain of pezo-1 function had surprisingly little effect on pharyngeal activity, causing only mild alterations in the duration and frequency of pumping induced by serotonin, and more obvious effects when challenged with high osmolarity solutions.Worms cultured in the laboratory are usually fed a diet of small, easily ingested Escherichia coli cells and, both loss and gain of pezo-1 function increased the pharynx’s response to this type of food. In their natural habitat, however, C. elegans encounter bacteria of various shapes and sizes, some of which might be harder to swallow. “It occurred to me that it might make a difference if we fed the worms with bacteria that were stiffer and longer,” Vásquez says.The researchers therefore provided their pezo-1 mutants with E. coli treated with cephalexin, an antibiotic that inhibits cell separation and causes the bacteria to form long, spaghetti-like filaments. Compared with wild-type worms fed with this diet, pharyngeal activity was markedly enhanced by the gain-of-function pezo-1 mutant, but substantially reduced in the absence of pezo-1, almost as if the worms were “choking” on the bacterial filaments.Crucially, by performing patch-clamp experiments on both cultured C. elegans cells and insect cells expressing recombinant pezo-1, Millet et al. confirmed that PEZO-1 is, indeed, a mechanosensitive ion channel. However, it remains to be seen exactly how PEZO-1 helps the pharynx sense the physical parameters of food and adjust its pumping activity accordingly. One possibility is that the channel acts within the proprioceptive neurons to regulate the release of serotonin.Intriguingly, the Drosophila PIEZO orthologue controls feeding behavior in flies (4). “However, it’s not known which mechanosensitive channels are important in the pharyngeal system of mammals,” Vásquez says. “Our studies in C. elegans could therefore open an opportunity to understand food sensation in humans.”     

香菇‘申香1644’的选育报告

香菇‘申香1644’是以传统优质栽培品种‘申香215’为亲本,采用多孢自交育种技术选育的新品种。其菌盖纵切面呈凸形,菌盖直径(6.15±0.38) cm,菌盖厚度(2.27±0.42) cm,菇型圆整,菇质紧实,产量高,生物学转化率95%以上。与亲本相比,‘申香1644’在分子标记和栽培性状上均具有明显差异性,其菌盖为浅黄褐色,颜色较亲本浅;菌龄100-105 d,较亲本缩短5-10 d。‘申香1644’菌丝生长适宜温度为22-26 ℃,原基发育适宜温度为16-22 ℃,可在全国范围内进行代料栽培。     

斑玉蕈‘闽真5号’的选育报告

斑玉蕈‘闽真5号’品种系以‘闽真3号’与‘白玉-01’作为亲本,通过原生质体单核化杂交育种技术选育获得。该品种菌盖白色,呈半球形,表面斑纹少而小。鲜菇蛋白质含量2.1%,氨基酸总量1.43%。示范栽培表明,‘闽真5号’菌丝最适培养温度20-27 ℃,子实体生长发育温度12-17 ℃,袋栽菌包培养周期为110 d,出菇周期为28 d,平均单袋产量635.17 g/袋。该品种具有栽培周期短、产量高、商品性状好等优良性状,适用于袋栽工厂化周年栽培。