Sperm Atlas 2.0

A SEM image of a Barbary sheep sperm head provide an almost 3-D image of the cell surface.

A SEM image of a Barbary sheep sperm head provide an almost 3-D image of the cell surface.

We are approaching a very special anniversary in the Reproductive Physiology laboratory! In February 2014, we will be celebrating five years since the inception of the San Diego Zoo Sperm Atlas. We started with a simple idea: to use the decades of historical microscope slides to visually teach the world about the diversity in biology through one simple cell, the sperm cell. In my post Creating a Sperm Atlas, I explained how this online resource came to be and now, after five years, we are taking the Atlas in a new, exciting direction with the help of a few friends.

This past spring, I was chatting with Dr. Michael Berns, the founder of the Beckman Laser Center at the University of California, Irvine. Dr. Barbara Durrant, the director of our division, and Dr. Berns have a long history of collaboration, and many conversations with him have led to new projects. This particular conversation led to what I jokingly refer to as Sperm Atlas 2.0!

A gold coating is applied to the sample in a vacuum using the "sputtering process."

A gold coating is applied to the sample in a vacuum using the “sputtering process.”

During this chat, he offered to collaborate with us on the next generation of sperm atlas by producing scanning electron microscope (SEM) images of sperm cells from a wide range of species we would provide. SEM images provide an almost three-dimensional image of the cell surface, and therefore can reveal morphological features not visible with two-dimensional light microscopic imaging. Needless to say, my mind was racing at the thought of what these images might reveal. Sperm of the vast majority of the species in the San Diego Zoo and San Diego Zoo Safari Park collections have never been imaged at high magnification, so we would be entering a whole new world!

Six months later, I am swimming in images produced by Lih-Huei Liaw, or, as she prefers to be called, Leacky, at the Beckman Laser Institute. So far, Leacky has painstakingly produced hundreds of sperm SEM images from nine species and has seven more species waiting to be imaged. The species range from the California desert tortoise to the Sudan Barbary sheep, with some snake and bird species as well.

These images have already helped us make some changes to our evaluation protocols. After we received the latest images of red-fronted gazelle sperm, I realized I needed to take Dr. Berns up on his offer to visit his lab and watch the SEM procedure from start to finish. Leacky took us through the entire SEM process while educating us on the difference between a light microscope, which uses light and a series of lenses to visualize the cells, and scanning or transmission electron microscopes, which use a focused beam of electrons to produce an image.

A desert tortoise sperm head image will be added to the San Diego Zoo Sperm Atlas.

A desert tortoise sperm head image will be added to the San Diego Zoo Sperm Atlas.

She explained that sample preparation for SEM includes mounting a drop of sperm on a coverslip and applying a gold coating after it is dry, because the sample surface must be electrically conductive. This is done in a vacuum using the “sputtering process.” Once the sample is mounted and coated, it is placed into a special vacuum chamber that keeps the sample very still during imaging while an electron beam bombards the gold-coated surface of the sperm.

I was truly impressed with the artistry and patience involved in producing such detailed images, and I continue to be excited about the next set of images Leacky will send. Will it be the four-toed hedgehog sperm or the Malay great argus pheasant sperm? I don’t know, but I can’t wait to share them with the world!

Nicole Ravida is a research coordinator for the San Diego Zoo Institute for Conservation Research. Read her previous post, No Scientist is an Island.

Still quiet here.sas

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