Sperm Wars: Lily of the Valley Revisited

One of the stranger stories in olfactory science is the apparent ability of mammalian sperm to respond to the odorant bourgeonal, which to the human nose smells somewhat like lily of the valley. Speculation has been that this pleasant floral scent is also a secret signaling molecule that guides sperm to the egg, by activating the odorant receptor OR1D2 located on the sperm cell’s surface.

Adding to the strangeness is the fact that, unique among odorants that have been tested, men are more sensitive to bourgeonal than are women. Men more sensitive to bourgeonal, sperm able to detect it—there seemed to be a compelling narrative.

Now it appears that the entire lily of the valley story needs to be rewritten.

Back in 2011, researchers led by Timo Strünker at the Center of Advanced European Studies and Research, in Bonn, Germany, took a closer look at the biochemistry of sperm, specifically at the mechanism underlying the progesterone-induced calcium ion (Ca2+) influx. The calcium influx activates a number of key physiological responses in sperm, including chemotaxis. The thought had been that a cell-surface receptor activated by progesterone kicked off a series of biochemical reactions leading to the opening of the CatSper Ca2+ ion channel. Once the channel is open, calcium ions flood through and into the sperm cell.

What Strünker and his colleagues demonstrated in their paper in Nature is that the CatSper channel is not opened by activation of a separate progesterone receptor. Instead, the CatSper channel itself (or an associated protein) serves as the progesterone receptor. (To anthropomorphize a bit: if you a progesterone molecule, you hold the key that opens the door directly; you don’t need to ring a doorbell down the hall and have someone open the door for you from the inside.)

While of interest mostly to biochemists, the Nature paper was a warning shot over the bow of Team Bourgeonal. It meant that separate, specialized receptors, such as odorant receptors, were not necessary for the calcium influx. In 2012, Strünker and team fired directly amidships. In an intricate and exhaustive set of experiments, they showed that the CatSper channel is activated by all sorts of molecules, including steroids, prostaglandins, menthol, bourgeonal, and several other odorants such as cyclamal, helional, and undecanal.

In other words, you can activate the CatSper channel by looking crooked at it. Or, as the researchers put it, “Activation happens through promiscuous, extracellularly accessible site(s) either on the channel itself or on associated proteins.” And this activation takes place completely independent of any odorant receptor for bourgeonal.

Team Strünker hypothesizes that the promiscuous CatSper channel “serves as a polymodal sensor for multiple chemical cues that assist sperm during their voyage across the female genital tract.” The idea that sperm are specifically attracted to bourgeonal’s lily of the valley scent is, it seems to me, dead in the water.

The studies discussed here are “The CatSper channel mediates progesterone-induced Ca2+ influx in human sperm,” by Timo Strünker, Normann Goodwin, Christoph Brenker, Nachiket D. Kashikar, Ingo Weyand, Reinhard Seifert, and U. Benjamin Kaupp, published in Nature 471:382-386, 2011, and “The CatSper channel: a polymodal chemosensor in human sperm,” by Christoph Brenker, Normann Goodwin, Ingo Weyand, Nachiket D. Kashikar, Masahiro Naruse, Miriam Krähling, Astrid Müller, U. Benjamin Kaupp, and Timo Strünker, published in EMBO Journal, 31:1654-1665, 2012.

ISDP: Kenneth, What’s the Olfactory?

 

It’s a dismal, wet, foggy day in January. And it’s the thirteenth of the month, time for us to scrape the bottom of the winter-time ISDP barrel and see what we can serve up to our loyal, if somewhat morbidly inclined, fanbase. As usual at this time of year, there’s not a lot to report. A hat tip to the Tiffany Network for supplying our meager portion.

According to CBS-TV Channel 21 in Harrisburg, Pennsylvania, a lady called police when she woke up to “a foul smell coming from the vent system” from the apartment below hers. Police investigated and discovered the decomposed body of a middle-aged male, who may be that unit’s  tenant. Due to suspicious circumstances, they have launched a homicide investigation.

We went fossil hunting near Harrisburg years ago. The location was a shale slope beneath a freeway overpass by the Susquehanna River. It was rich with trilobites. We nearly got beaned by a Rolling Rock bottle flung out of a passing car. Telling this story makes us hungry for that central Pennsylvania specialty—scrapple. In our opinion, Habbersett® brand scrapple is by far the best. Sadly, stores near FirstNerve Manor no longer carry it.

CBS affiliate Channel 4 in Miami, Florida has the second incident. A tenant in a retirement home near Miami Gardens called the landlord to report a “bad smell” that had been coming from a neighbor’s apartment for a couple of days. The landlord, in turn, called the neighbor’s granddaughter who entered the apartment and found her grandmother dead and her grandfather unconscious. The new report discusses a malfunctioning gas stove and oven, yet the neighbor didn’t report smelling a gas leak. Hmm . . .

We’ve often acknowledged that dealing with ISDP complaints is an occupational hazard for apartment building managers and maintenance workers. So we understand why they’d like to hand off a complaint like this one. But asking the tenants’ granddaughter to look in on the scene strikes us as a poor call.

It’s Not What You Think It Is

What do you mean, “what is it?” It’s a scent stick, duh.

Harmon Scents has packed some of its popular scents into rub-on sticks that are easy to use and effective.

What’s not to get?

The sticks can be used for all manner of applications, including on clothing, scent wicks or on natural features such as rocks, stumps or vegetation.”

Still unclear on the concept? Try this:

. . . the sticks are available in 10 varieties, including Triple Heat, Dominant Buck, Bear-Cinnamon, Coyote, Fox, Doe Pee and Herd Blend-whitetail.

Right! It’s the Bull Elk Scent Stick.

Nissan Edges Toward a Logo-Scent

A custom scent is part of the enormous, multisensory Nissan exhibit that will tour ten global auto shows this year, beginning with next week’s North American Auto Show.

. . . the Nissan display features its own special scents and sounds, carefully choreographed to create a complete experience for visitors. A distinctive fragrance will be periodically released into the display area and the mood-setting background music will change with a subtly different vibe and energy for morning, mid-day and evening.

Nice touch!

In a video, Roel de Vries, Nissan’s VP of global marketing strategy, describes the scent as modern, vibrant, and exciting. He also calls it is “Oriental” while referencing the fact that Nissan is a Japanese company; so it’s not clear that it smells Oriental in the perfumer’s meaning of the word.

De Vries says that if the scent works well at the trade shows, Nissan may deploy it in the company’s dealerships.

Don’t Blame the Methane

There is a popular misconception that methane gas is stinky when, in fact, it is almost odorless. Methane (CH₄) is the chief component of the natural gas delivered by your utility company. The company adds an obnoxious sulfur-containing chemical to the product as a warning agent for leaks. People who don’t know better conclude that the methane itself stinks.

The misconception is reinforced in local press reports about odor problems at garbage dumps and landfills. Methane and other gases are generated by bacterial activity as food scraps decompose. However, the rotten smell emerging from the trash heap is not due to the methane, but to other molecules that do stink. Depending on the type of waste and local conditions at the dump, the smell can get pretty intense.

In some landfills the volume of methane is large enough to create a threat of combustion. Then it must be collected via pipes and vented or burned. Sometimes it pays to use it to fuel a steam plant or electrical generator. These systems collect and burn foul-smelling non-methane gases as well, which may make the landfill somewhat less stinky. Then again, it may not.

Now consider yesterday’s headline in the Taunton [Massachusetts] Daily Gazette: “Company vows to eradicate foul odor at Taunton landfill.”

The story, by staff reporter Charles Winokoor, begins this way:

The smell that has elicited complaints from residents living near the city’s landfill should soon be a thing of the past, representatives of a methane gas conversion firm told city councilors Tuesday night. 

“It concerns us as well. We want to fix this,” said Anthony Falbo, senior vice president of operations for Fortistar Methane Group. 

Fortistar has a contract with Waste Management, which manages the city’s landfill. 

Falbo said he and his staff weren’t aware of a growing odor problem until recently, when City Council solid waste committee chairman Daniel Barbour publicly raised the issue.

Fortistar says it will soon add more methane gas extraction wells to those already on site. Yet reading the entire story, it isn’t clear whether Fortistar’s Mr. Falbo or Taunton councilman Barbour are clear on the concept: do they blame the odor on methane or do they just assume that collecting more gas of all types will eliminate the odor problem?

Should the new methane extractors not solve the problem, it’s a question that may come back to haunt the town and its vendors. Clarity now could head of a PR kerfuffle later.

Related: My Green and Stinky posts document the unwillingness of municipal composting operators to come clean about the inherent stinkiness of their facilities. Communities should be better informed and more skeptical about airy claims of odorlessness by all waste management vendors.