The long and short of sperm tails

August 5, 2011
Giant mitochondria in the tail of fruit fly sperm elongate and show an increase in length, while the volume remains constant. Credit: 2011 Shigeo Hayashi

A team of biologists in Japan has uncovered an unexpected role for mitochondria1, the power houses of cells, in the development of sperm in the fruit fly Drosophila melanogaster.

Drosophila melanogaster belongs to a family of two-winged called the drosophilids. Some drosophilid species have sperm with short tails, but others have exceptionally long tails. Males of D. bifurca, for example, produce sperm with tails that are over twenty times as long as the insect itself. “The diversity of sperm morphology among drosophilid flies has long fascinated reproductive and evolutionary alike,” says Shigeo Hayashi of the RIKEN Center for Developmental Biology, Kobe, who led the team.

Biologists believe that the long sperm found in some drosophilid species evolved in response to strong post-mating selection driven by ‘sperm competition’, the race between sperm from different males to fertilize an egg. Longer sperm would have the advantage of positioning their head closer to the egg.

Sperm movement is driven by waves that propagate along a hair-like motile structure called the flagellum within the sperm tail. The flagellum core, called the axoneme, is composed of microtubules formed of tubulin molecules arranged in chains. “We were aware from previous studies using mutant flies that the axoneme is dispensable for sperm cell elongation, so we set out to understand the underlying mechanism,” explains Hayashi. 

In addition to the axoneme, the membrane-bound sperm tails of insects typically contain giant mitochondria that extend along their entire length, as well as free microtubules. Working with D. melanogaster, Hayashi and his colleagues showed that sperm tail growth is driven by the mutually dependent extension of the giant mitochondria and microtubules that form around them (Fig. 1).

Experiments with cultured spermatids, the precursors of sperm, revealed that sperm elongation crucially depends upon the integrity of mitochondria and the reorganization of microtubules at the growing tip. In addition, the researchers found that the essential sliding movement of microtubules at the tip requires accumulation of Milton, a mitochondria–microtubule linker protein.

Hayashi and colleagues showed that experimentally disrupting Milton and its associated protein dMiro, as well as the potential microtubule cross-linking proteins Nebbish and Fascetto, caused defective tail elongation, resulting in abnormal sperm. They also showed that spermatid tail elongation requires both the association between mitochondria and microtubules, and microtubule cross-linking. “We have demonstrated that form a structural platform for microtubule reorganization, which supports robust elongation at the growing tip of the long tail,” Hayashi concludes.  

Explore further: Rodent sperm work together for better results

More information: Noguchi, T., et al. Sustained elongation of sperm tail promoted by local remodeling of giant mitochondria in Drosophila. Current Biology 21, 805–814 (2011). www.riken.jp/engn/r-world/research/lab/cdb/mor/index.html

Related Stories

Rodent sperm work together for better results

January 24, 2007

Although, sperm are inseminated in millions each sperm goes it alone. However, under some circumstances it might be advantageous for sperm to cooperate with one another. This is especially likely to be the case when females ...

Viagra could be harmful to fertility

February 25, 2008

A study to be published in the British medical journal Fertility and Sterility suggests that Viagra could harm men's fertility.

Sperm size isn't everything

November 25, 2008

Contrary to common scientific belief, the length of a sperm's tail does not always determine how fast it can swim. Research published in the open access journal BMC Evolutionary Biology has shown that in the counter-intuitive ...

Hens' sperm ejection secrets

August 3, 2011

In reproductive warfare sperm is a male’s ultimate weapon to decide who fathers the next generation.

Recommended for you

Genomes uncover life's early history

August 24, 2015

A University of Manchester scientist is part of a team which has carried out one of the biggest ever analyses of genomes on life of all forms.

Rare nautilus sighted for the first time in three decades

August 25, 2015

In early August, biologist Peter Ward returned from the South Pacific with news that he encountered an old friend, one he hadn't seen in over three decades. The University of Washington professor had seen what he considers ...

Study shows female frogs susceptible to 'decoy effect'

August 28, 2015

(Phys.org)—A pair of researchers has found that female túngaras, frogs that live in parts of Mexico and Central and South America, appear to be susceptible to the "decoy effect." In their paper published in the journal ...

Why a mutant rice called Big Grain1 yields such big grains

August 24, 2015

(Phys.org)—Rice is one of the most important staple crops grown by humans—very possibly the most important in history. With 4.3 billion inhabitants, Asia is home to 60 percent of the world's population, so it's unsurprising ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.