Rapid Preparation of Thick Sections of Fleshy Plant Tissues

Methods are described for permanent micro-slide preparations of soft, large-celled plant tissues such as ripe fruit. Thick sections (200-800 [t) cut on a sliding microtome are aspirated in an aqueous killing agent; after fixing and washing, the sections are dehydrated and cleared in an alcohol-xylene series. Infiltration with 20, 30, and 40% solutions of mountant prior to mounting the sections is necessary to avoid too abrupt changes in the cleared tissues. Several staining methods have been successfully used for different purposes. The final preparations showed nearly perfect preservation of intact cells and intercellular spaces in their 3-dimension-al structure.     

A Jungle in There: Bacteria in Belly Buttons are Highly Diverse,but Predictable

The belly button is one of the habitats closest to us, and yet it remains relatively unexplored. We analyzed bacteria and arachaea from the belly buttons of humans from two different populations sampled within a nation-wide citizen science project. We examined bacterial and archaeal phylotypes present and their diversity using multiplex pyrosequencing of 16S rDNA libraries. We then tested the oligarchy hypothesis borrowed from tropical macroecology, namely that the frequency of phylotypes in one sample of humans predicts its frequency in another independent sample. We also tested the predictions that frequent phylotypes (the oligarchs) tend to be common when present, and tend to be more phylogenetically clustered than rare phylotypes. Once rarefied to four hundred reads per sample, bacterial communities from belly buttons proved to be at least as diverse as communities known from other skin studies (on average 67 bacterial phylotypes per belly button). However, the belly button communities were strongly dominated by a few taxa: only 6 phylotypes occurred on >80% humans. While these frequent bacterial phylotypes (the archaea were all rare) are a tiny part of the total diversity of bacteria in human navels (<0.3% of phylotypes), they constitute a major portion of individual reads (∼1/3), and are predictable among independent samples of humans, in terms of both the occurrence and evolutionary relatedness (more closely related than randomly drawn equal sets of phylotypes). Thus, the hypothesis that “oligarchs” dominate diverse assemblages appears to be supported by human-associated bacteria. Although it remains difficult to predict which species of bacteria might be found on a particular human, predicting which species are most frequent (or rare) seems more straightforward, at least for those species living in belly buttons.     

Not(ch) just development: Notch signalling in the adult brain

The Notch pathway is often regarded as a developmental pathway, but components of Notch signalling are expressed and active in the adult brain. With the advent of more sophisticated genetic manipulations, evidence has emerged that suggests both conserved and novel roles for Notch signalling in the adult brain. Not surprisingly, Notch is a key regulator of adult neural stem cells, but it is increasingly clear that Notch signalling also has roles in the regulation of migration, morphology, synaptic plasticity and survival of immature and mature neurons. Understanding the many functions of Notch signalling in the adult brain, and its dysfunction in neurodegenerative disease and malignancy, is crucial to the development of new therapeutics that are centred around this pathway.     

Some observations on the diurnal variation of mitosis in the stratified squamous epithelium of wounded tympanic membrane

Summary A study of mitosis in the stratified squamous epithelium of the tympanic membrane of the guinea-pig was made after wounding this organ at 09.00 h in one series of animals and at 21.00 h in a second series. It was found that the diurnal variation of mitosis was abolished by the injury. This finding corresponds with a basic requirement of the chalone-adrenaline hypothesis which is considered to be a factor in the mitotic control of epidermal cells. It was also found that the maximum number of dividing cells was at the wound edge in the group wounded at 09.00 h, which also agrees with the chalone concept. In the group wounded at 21.00 h, however, the initial mitotic response was in cells distally placed from the wound edge which is more difficult to explain. Perhaps these cells are inhibited mitotically by the factors normally producing a low nocturnal mitotic rate and undergo migration to cover the defect in the first instance, and only divide at a later time when the mitotic inhibition is lifted. It appears that the factors responsible for the increased mitotic rate after wounding are different from those responsible for the diurnal variation.The author wishes to express his thanks to Professor R.M.H. McMinn for his support of this work