Science is the poetry of Nature.







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Posts tagged "cell"

bpod-mrc:

18 October 2013

Drug Smuggler

Some naturally occurring proteins interact with medicines in surprising ways. A protein called P-gp, for example, sits on the cell surface and shuttles a broad range of drugs out wards. It plays a role in multidrug resistance in cancer – if it becomes abundant the cancer cells can eliminate not only the current medicine, but a host of others too, leaving the patient with few options. Scientists studying asthma are also interested in this protein because it could influence the absorption of medicines taken by inhaler. Pictured is a human airway surrounded by epithelial cells (green) with P-gp highlighted in red. Asthma medicines are often only required at the lung surface and some produce side effects elsewhere in the body. So P-gp might act as a natural barrier preventing drugs from crossing into the blood supply. A better understanding of this protein’s role is important for the development of new medicines.

Written by Julie Webb

Image by Holly Brooker, an entrant in the Society of Biology 2012 Photography competition
Part of the Society of Biology’s ‘Biology Week’
Image provided by the Society of Biology
Research published in the Journal of Pharmaceutical Sciences, September 2013

Lung Cancer Cell Dividing

This is a scanning electron micrograph (STEM), coloured by Steve Gscheissner, of a lung cancer cell dividing. The two daughter cells remain temporarily joined at the cytoplasmic bridge.

heythereuniverse:

Radial growth of sensory neurons | María Alejandra Lopez-Verrilli
Axons stained in green, somas in blue and actin filaments in red (4x).

heythereuniverse:

Radial growth of sensory neurons | María Alejandra Lopez-Verrilli

Axons stained in green, somas in blue and actin filaments in red (4x).

amolecularmatter:

“Weird Life”: The Story of the Cell

“The synthesis of life, should it ever occur, will not be the sensational discovery which we usually associate with the idea. If we accept the theory of evolution, then the first dawn of the synthesis of life must consist in the production of forms intermediate between the inorganic and the organic world, forms which possess only some of the rudimentary attributes of life, to which other attributes will be slowly added in the course of development by the evolutionary action of the environment.” - Stephane Leduc, 1911

In July 2007, a group of scientists associated with the American Research Council issued a report about something they termed “weird life.” Weird life, they said, could be life in a form that we have never seen before - an organism may not depend on water, for example, or it may have a completely different, non-nucleic-acid based system of heredity and still be alive. Their definition of weird life was vague, and not by accident: One of the primary challenges in the discussion of life, both on earth and elsewhere in the universe, is that life itself is a very difficult thing to parameterise. As David Greer, a professor of physics at New York University, says, “There is no mathematically rigorous definition of life.” Our determination of life is based entirely on our own human experience, and thus its working definition is less a set of functional rules for classification and more a set of somewhat ambiguous statements designed to organise the unknown. The precise problem with trying to organise the unknown, of course, is that nothing is known about it; but without a reconcilable definition of life - or “weird life”, as the case may be - we don’t even know where to start looking.

The key, I think, to this almost certainly inaccurate (and definitely not mathematically rigorous) but working definition is to explore how life came about in the first place. This serves two purposes: First, the definition of life could arguably be based on the most basic conditions necessary for it to occur, and second, life in its most rudimentary forms are more likely to be homogenous across biological systems (however more complex or different from our own) than the large-scale plants and animals we traditionally associate with life. In addition, the makeshift definition should be written as a set of provable postulates, and should be sufficiently inclusive to potentially apply to all forms of aptly labeled “weird life” without being overly promiscuous, so to speak.

The Primordial Soup’s Gone Off

Ever since Stanley Miller’s infamous experiment in 1953, the long-time leading hypothesis into the origin of life was his theory, built around the reducing atmospheric gases of early earth and electric charge passing through them in the form of lightning. Miller’s experiment, which has been replicated, successfully showed that shooting a spark through reducing gases in a laboratory beaker produces biomolecules - in Miller’s case, approximately 10 amino acids and several nucleic acid precursors, although others who have repeated the experiment have had rather more success. The experiment illustrates clearly that life could have begun this way.

image

Of course, the origin of life is still a black box; in reality any number of plausible hypotheses could be correct. However, for me there are several unaddressed issues in Miller’s experiment that make me skeptical that it is the whole story behind the evolution of us. The primary issue is simply time; the earth is only 4.5 billion years old, and the oldest microfossils of early cell-like structures that have been found date back 3.5 billion years. While a billion years seems like - well, a billion years to us, it’s actually quite quick on an evolutionary timescale. To me, this means that life didn’t simply come down to a lucky lightning strike - it indicates that there was a driving force behind its development that pushed it forward faster.

In 1993, a different theory for the origin of life - termed the hydrothermal vent idea - came into prevalence. It suggested that instead of a collection of atoms in the early ocean, life came out of deep-sea hydrothermal vents. There is much compelling evidence for this idea; two of the most compelling bits, I think, are the existence of an energy disequilibrium and the interconnected micropores found on the vents’ surface. 

The ocean, even on the early earth, was a fairly stagnant place in terms of energy gradients; lightning strikes could perhaps have caused them sporadically, but in different locations and to varying degrees with very little continuity. Hydrothermal vents, on the other hand, are rich in energy disequilibrium, boasting temperature, pH, and redox gradients. 

So why are energy gradients so important? Because for cells, harnessing energy as ion gradients is about as universal as the genetic code. A new paper recently published in Cell postulates that tiny micropores found on the surface of deep-sea vents - conveniently approximately the diameter of a cell - could have been the starting point of life on earth. In modern cells, about 75% of a cell’s ATP budget - or biological energy - goes into making proteins; conversely, ATP is replenished by proteins that harness chemiosmotic gradients. The paper postulates that the energy disequilibrium provided by hydrothermal vents - specifically, that sustained disequilibrium at a submarine hydrothermal vent interfacing with ocean water - generates conditions that thermodynamically favour the formation of life’s building blocks, particularly amino acids, in the presence of hydrogen gas, carbon dioxide, and ammonium. If a leaky membrane built of lipid precursors accumulated near a vent, the budding system would have a ready-made metabolism by exploiting the pre-existing chemiosmotic gradient. Once enough precursors accumulated, and the “metabolism tap” was shut off due to the newly formed “membrane“‘s impermeability, natural selection would strongly favour cells with simple antiporters that could continue to exploit the ion gradient. 

Defining Life from Vents

If, for the sake of argument, the thermal vent hypothesis is found to be the way things actually were, what then? What about life? Defining life by the characteristics of the first cell does not appeal to me; this leads to a definition of characteristics that are shared because they originate from a common ancestor, and not because they are actually fundamental to life. However, the hydrothermal vent hypothesis does, I think, enhance our understanding of what is needed for life, at least on this planet, and based upon the need for a biochemical gradient for protein production and the necessity of a lineage to exploit progress made in the previous generation, I would define life as:

  1. A physical compartment across the walls of which energy can be generated and utilised for biochemical reactions, and; 
  2. one that possesses a material of heredity that may be passed to the next generation.

It’s not a particularly restrictive definition, nor is it likely broadly accurate. However, the fact remains that there are many definitions of life; few widely agreed upon, and certainly none reasonably consented to in their entirety without special cases. Considering what was necessary for the first cell to form is as valid a method of organising the unknown as any other, and perhaps, one day, we’ll be able to find a distinctly new organism somewhere in the universe, one that shifts our entire paradigm on biochemistry, heredity, and what it means to fundamentally be alive. Until then, I think, formal and constructive definitions will elude us, and “weird life” will continue to be - well, weird.

An Afterthought: The Interesting Case of Protocells

In his TedX talk, Martin Hanczyc outlined a very similar definition of life to the one I derived from the assumed origin of life inside thermal vents. It can be reasonably summarised in three words:

  1. Body;
  2. Metabolism;
  3. Heredity.

He works extensively with oil and water systems, designing in vitro protocells. He also works with tar systems to simulate the stuff of the early universe, like those in the images at the top of this post; his protocells are comprised of single-digit numbers of chemicals, and yet are able to locate food, respond to one another within an environment, and even divide and hybridise into wholly new organisms with new functional characteristics. 

So are these protocells alive? Martin Hanczyc believes that nothing can be considered “alive” in a black-and-white way; rather, these protocells fall somewhere in the range of an intermediate between the inorganic and organic world, and while they possess some attributes necessary for life they simply fall on a continuum along with humankind and this desk. A video of his TedX talk, in which he explains further, can be found here.

image

Due to its length and their quantity, references in this post are cited using links where they are most relevant. Most of the information used comes from a new paper in Cell on the Origin of Membrane Bioenergetics (Martin and Lane, 2012), and Martin Hancycz’s TedX talk. For another take on Martin Hancycz’s work, see this post here.

amolecularmatter:

The cerebral vasculature is a complex network that allows only 18% of the total blood volume of the body through the delicate tissues of the brain. This allows the transport of oxygen and nutrients that are essential to brain function. In the wide field, plane-projection confocal image above, the superficial cerebral vasculature of a mouse - specifically the actinα-N-acetylgalactosamine residues, and DNA in cell nuclei - are labeled in situ.

Image Source: The Cell Picture Show.

science-junkie:

Turning vast amounts of genomic data into meaningful information about the cell is the great challenge of bioinformatics, with major implications for human biology and medicine. Researchers at the University of California, San Diego School of Medicine and colleagues have proposed a new method that creates a computational model of the cell from large networks of gene and protein interactions, discovering how genes and proteins connect to form higher-level cellular machinery.

The findings are published in the December 16 advance online publication of Nature Biotechnology.

“Our method creates ontology, or a specification of all the major players in the cell and the relationships between them,” said first author Janusz Dutkowski, PhD, postdoctoral researcher in the UC San Diego Department of Medicine. It uses knowledge about how genes and proteins interact with each other and automatically organizes this information to form a comprehensive catalog of gene functions, cellular components, and processes.

“What’s new about our ontology is that it is created automatically from large datasets. In this way, we see not only what is already known, but also potentially new biological components and processes – the bases for new hypotheses,” said Dutkowski.

(via Toward a new model of the cell)

medicalschool:

SEM of a single red blood cell on the tip of a needle

(via kenobi-wan-obi)

frontal-cortex:

Fig. 7. Effect of PDGF-BB on microfilament reorganization, as revealed by phalloidin staining. Quiescent mesonephric mesenchymal cells (A) were stimulated for 15 minutes (B) with PDGF-BB (10 ng/ml). Note that treated cells exhibit a rapid change in microfilament reorganization and in cellular morphology (phalloidin staining at the leading edge of the cell and extensions of lamellipodia). Bar, 20 μm.

Antonella Puglianiello et al, Expression and role of PDGF-BB and PDGFR-β during testis morphogenesis in the mouse embryo; Journal of Cell Science, March 1, 2004 vol. 117 no. 7 1151-1160

The role played by PDGF in testis morphogenesis is still incompletely understood. The present study investigates the expression and potential role of platelet-derived growth factor-BB (PDGF-BB) and its receptor, PDGF receptor β (PDGFR-β), during mouse testis cord formation, and the possibility that the growth factor may be involved in the migration to the gonad of mesenchymal cells of mesonephric origin.

nyanning:

Design for Corner Lithography

The structure pictured below is a “microscopic pyramid,” New Scientist explains, “a cage for a living cell, constructed to better observe cells in their natural 3D environment, as opposed to the usual flat plane of a Petri dish.

It was constructed “by depositing nitrides over silicon pits. When most of the material is peeled away, a small amount of material remains in the corners to create a pyramid.”

This is called corner lithography, a technique used for creating the “cell trapping device” seen above.

The Giza-like, seemingly alien geometry of the pyramidal cage compared to the wild and barely containable spheroid burr of the cell itself is remarkable. The literally monstrous vitality of the cell caught inside the imposed order of the pyramid offers us an image of two fundamentally opposed methods of material organization in conflict with one another, a collision of orders as if the Gothic met the Doric or the Baroque met the Romanesque. 

Interestingly, though, at least according to New Scientist, “Because the pyramids have holes in the sides and are close together, the cells can interact for the most part as they naturally do.” In other words, these apparently oppositional modes—the fuzzy and the straight—incredibly, even miraculously, don’t interfere with one another at all.

Functionally speaking, it’s as if, from the cell’s perspective, the pyramid isn’t even there.

(via BLDGBLOG)

(via kenobi-wan-obi)

afracturedreality:

Winner of Honorable Mention in Olympus’ BioScapes Digital Imaging Competition® of 2010.

Shown here is the polarized light micrograph of a Diatom arachnoidiscus. Diatoms encase themselves in an outer cell wall called a frustule, which is composed of silica, or glass. Although these glass frustules provide diatoms with structure and defense, they are also extremely beautiful.

By Michael Shribak, Marine Biological Laboratory, Woods Hole, MA, USA

(via kenobi-wan-obi)

sciencenote:

To Be Hairy is to Be Mammal

By Ian Smyth, Monash University, Australia

Hair grows over the entire human body, except for our lips, palms of our feet and hands, and two other smooth organs. Hair sprouts from a skin organ, called the “hair follicle.” A group of epithelial cells and melanocytes sit at the base of the hair follicle produce the hair fiber by rapidly dividing. The hair follicle is connected to the epidermis by a set of muscles— the arrector pili— which generate “goosebumps” by pushing the hair up. Near these muscles, a group of stem cells sit inside a structure called, “the bulge” (dark blue), continually supplying the follicle with hair-producing cells.

Image: Hair follicles in a mouse epidermis immunolabeld and then imaged with confocal microscopy.

sciencenote:

A Watchful Welcome

Our bodies have bustling transport networks, thriving day and night with a traffic of blood, water and nutrients. Unfortunately, cancer cells sometimes use these natural highways to hitchhike their way between vulnerable tissues. The success of their journey, known as metastasis, depends on how well they adjust to living in a new place. This section of a mouse kidney (highlighted in red) has been transplanted with cells from the pancreas (highlighted in green). The image was taken through a glass ‘window’ stuck to the skin – offering a peek at the welcome these migrant cells received. The friendly kidney cells spread their blood vessels out towards their new neighbours, enabling them to grow (the assembly of vessels magnified on the right is 400 times smaller than an outstretched hand). Watching how cancer takes advantage of the hospitality of human tissues may influence new therapies designed to send travelling cancers packing.

Written by John Ankers

(via kenobi-wan-obi)

medicalschool:

Embryo at the 4-cell stage

(via kenobi-wan-obi)

afracturedreality:

A single bundle of stereocilia (green) projects from the epithelium of the papilla, a sensory patch in amphibian ears. We can enjoy music and hear the city traffic because of stereocilia bundles in the inner ear. These actin-rich bundles protrude from the apical surface of hair cells lining the inner ear and vibrate in response to sound waves.

By Leonardo Andrade and Bechara Kachar, NIDCD/NIH

(via kenobi-wan-obi)

afracturedreality:

SEM of a cross-section through the cochlea, false colored to reveal the distinct functional units of the mammalian organ for hearing: mechanosensory hair cells (blue), supporting cells (pink), and highly specialized extracellular matrix structures (ECM, green). Although all hair cells in the cochlea have similar organization and the same basic function, the broad range of sensitivity and exquisite frequency selectivity of each hair cell depends on its micromechanical properties and its relationship to the local architecture.

By Bechara Kachar, NIDCD/NIH

(via kenobi-wan-obi)