Friday, March 25, 2011

Progesterone's action on sperm finally solved

Two recent articles in Nature reveal a mystery that's been puzzling physiologists for a couple of decades . . . how does progesterone signal sperm cells?

The short version of the story is this . . .

Progesterone is released from the cumulus cells that cling to the outside of the zona pellucida surrounding the ovum. This progesterone binds directly to calcium channels in the sperm's plasma membrane to open.  Influx of calcium ions triggers an increase in flagellum activity.  This increased work is needed for the sperm to get through the zona to the ovum.

Progesterone is a steroid hormone and thus usually enters its target cell and activates transcription of a gene.  In this case, however, progesterone instead directly triggers a calcium channel.  It's not even a second-messenger system, but a direct binding to the channel.

Secretion of progesterone by cumulus cells apparently also provides a chemical gradient that helps sperm navigate toward the ovum.

Recall also that calcium influx into the ovum triggered by contact with a sperm cell plays a role in producing changes within the ovum that result in successful fertilization.

I recommend that my students keep running concept lists on recurring themes or actors in story of human biology.  Here's something they can now add to their calcium list.  Now they can see that a calcium gradient is a truly multipurpose tool in the body.  (For more about running concept lists see

Want to know more?
Sperm mystery solved: Scientists identify the channel by which progesterone activates sperm to swim toward an egg
M. Scudellari
The Scientist Published online 16th March 2011
[Nice summary of the significance of the discovery]

Female hormone could be key to male contraceptive: Progesterone-sensing molecule that guides sperm to egg offers fertility solution.
E. Callaway
NatureNews Published online 16 March 2011 | Nature | doi:10.1038/news.2011.163
[Summary article outlining the papers published in Nature]

Progesterone activates the principal Ca2+ channel of human sperm
Lishko et al.
Nature  471:387–391 17 March 2011 doi:10.1038/nature09767
[Original research findings]

The CatSper channel mediates progesterone-induced Ca2+ influx in human sperm
Strunker et al.
Nature 471:382–386 17 March 2011 doi:10.1038/nature09769
[Original research findings]
From The A&P Professor archive
New discovery about sperm's ability to swim
K. Patton
The A&P Professor published online Feb 18, 2010
[Summary of new discovery that when sperm enter female tract, proton channels in the sperm head open and the resulting pH drop triggers influx of calcium, which gets the flagella started in the first place.  That darn calcium shows up in every part of this story, eh?]

Wednesday, March 16, 2011

What do tuft cells do?

We've known for a half-century that the lining of the small intestine has a scattering of weird little cells called tuft cells.  They are called that because they have distinctive tufts of microvilli facing into the intestinal lumen.  But what do they do?  We're finally getting to the answer!

A recent article in Journal of Cell Biology outlines confirms some recent discoveries about tuft cell function and extends our knowledge a bit further.

Apparently, tuft cells are secretory cells that produce opioids in the gut.  They are also the only epithelial cells that produce the COX (cyclooxygenase) enzymes needed to produce prostaglandins involved in inflammation and tumor formation.

Some physiologists had previously proposed a sensory role for tuft cells.  Could they be involved in tasting foods in the gut and be part of the signaling mechanism that regulates exocrine and endocrine secretion that controls digestive and metabolic processes?

As we learn more about tuft cells, we are sure to discover a role for them in normal regulation of intestinal function as well as in important pathological processes. 

Want to know more?

A fifth amendment to the intestine's constitution
Ben ShortJournal of Cell Biology 2011 192:706. Published March 7, 2011, doi:10.1083/jcb.1925iti2
[Brief synopsis of the discovery and its importance]

Distinct ATOH1 and Neurog3 requirements define tuft cells as a new secretory cell type in the intestinal epithelium.
Gerbe, F., et al.
Journal of Cell Biology 2011 Mar 7;192(5):767-80. doi:10.1083/jcb.201010127.
[Original research article.  Includes many illustrations, supplements, helps and cross references. FREE full text]

Here's a really nice teaching image from the Gerbe et al. article, which complements Figure 25-18 in the Anatomy & Physiology 7/E textbook: (includes downloadable PowerPoint slide)

Here are all the PowerPoints available with the Gerbe et al. article:

Chemosensory Perception in the Gut 
Hofer, D., et al.
Physiology February 1999 vol. 14 no. 1 18-23  
[Article proposing sensory function of tuft cells; FREE access to full text/PDF; nice images]


Saturday, March 12, 2011

More study tool slides

In a recent post, I briefly discussed some presentations that I do regarding using Running Concept Lists and Concept Maps to learn anatomy and physiology concepts and how they relate to one another.  I posted links to slides, narrated YouTube videos of brief versions of the presentation, and related study tip pages in my Lion Den website for students.  As promised, this week I'm posting links and short descriptions of four more presentations that may help your students succeed in A&P.

Want to present your own version of any of these study tips? Perhaps embed parts of them into your own presentations? You are welcome to use the slides, which can be found in the Lion Den Slide Collection.  (To use the slides, you'll need the password for downloading them.  Just fill in the form to get the password if you don't already have it.)

Don't forget . . . when using the direct links below, you need to have the super-secret, magic password ready!

In an upcoming post, I'll let you in on some secrets for creating some additional time with you students so that you can cover these study tips without sacrificing "content time" in your A&P course.

Previously described slides available in the Lion Den Slide Collection:

More Slides also available in the Lion Den Slide Collection:

Flash Cards: Reducing Your Study Time 
Some practical tips for using study cards to reduce your study time and get a solid foundation in learning any topic. This video also includes some surprising advanced techniques that show how to use flash cards to also learn higher-level thinking in any subject. Includes discussion of the Leitner system (plus Patton's adaptation of the Leitner system), color codes and symbols, using cards to learn processes and ordered structures, and using cards to build concept maps (mind maps).
Muscle Names Have Meaning
Learning muscles is hard enough without dealing with those crazy convoluted Latin names. But if you pay attention to those names, you'll find that they are actually phrases that help you find the muscles AND help you to remember them in the long term. Find out how this works . . . and where to find lists to help you figure out the meaning of common muscle names.
Exam Strategies
Proven strategies for success in taking tests and exams. What you can do before, during, and after an exam to improve performance in your anatomy and physiology course.
Learn from Your Mistakes: TEST ANALYSIS 
How do you effectively "go over" your tests or exams? Learn how to analyze your tests to see what went wrong and how to fix it.

Don't forget that your students can keep up with all these study tips (and more) on their own by subscribing to my blog The A&P Student.

I have some handy (and bizarre) bookmarks giving students information about The A&P Student blog that you can distribute FREE to your classes!  Just go to my bookmark request page to get bookmarks for your students now.

    Friday, March 11, 2011

    Antibodies work INSIDE virus-infected cells

    You already know that we use antibodies in several ways to combat infection in our immune system.  They bind to pathogens, they activate complement, you know the drill. Well, here's another bullet point to add to your antibody slide: we've found a new intracellular role for the antibody.

    Researchers have recently shown that antibodies can attach to a virus, which then enters a host cell where a molecule called TRIM21 quickly binds at Fc on the IgG antibodies.  By ubiquitin ligase activity, TRIM21 targets the virus's proteins for destruction by the proteasome.

    Click here for an awesome animation that shows all this violent destruction in a simple, dramatic way. Your students will love this animation, because the proteasomes' rapid and total destruction of the virus is so amazing to watch.  And it's a good opportunity to emphasize the importance of the proteasome in the cell. 

    Not only does this observation give us a new intracellular role for antibodies, it also highlights a new and important strategic link between innate immunity (TRIM21/proteasome action) and adaptive immunity (antibodies).

    Want to know more?

    Antibodies mediate intracellular immunity through tripartite motif-containing 21 (TRIM21)
    Donna L. Mallery, et al.
    Proceedings of the National Academy of Science November 16, 2010 vol. 107 no. 46 19985-19990
    Published online before print November 2, 2010, doi: 10.1073/pnas.1014074107
    [This is the original paper, available open access]

    Read this shortened evaluation highlighting the key findings:
    Koch D, Sawtell N: 2010.

    Come Inside
    R. Grant
    The Scientist Volume 25 Issue 3 Page 58 2011-03-01
    [Quick and easy summary, including that awesome video]

    AntibodyBy the way, I love those movies showing miniaturized submarines exploring the inside of the body . . . and this reminds me of the SyFy thriller Antibody with Lance Henriksen and Robin Givens.  Yes, it's a hokey movie, but I like the scenes showing the immune cells attacking the miniaturized sub.