As she closes the door to her lab after a career spanning six decades, Clara Franzini-Armstrong, PhD, opens a window to discovery for future generations of scholars with her vast repository of muscle micrographs.

By Meredith Mann

 Clara Franzini-Armstrong surrounded by ring binder volumes that hold prints of electron micrographs

Portrait of a young scientist: In this photo, the electron microscope is not visible, but Franzini-Armstrong is surrounded by ring binder volumes that hold prints of electron micrographs that formed the large collection acquired over several decades of research.
Skeletal muscle from a frog
An orderly hop: In skeletal muscle from a frog, the filaments of contractile molecules that form the sarcomere are highly ordered due to an extensive arrangement of cross links.

It was love at first sight when, as a second-year student at the University of Pisa in Italy, Clara Franzini saw the published images of kidney tissue that had just been imaged in the electron microscope for the first time. She was immediately taken: “They are quite artistic!”

More than 60 years later, Clara Franzini-Armstrong, PhD, is a legend in the field of electron microscopy, and an institution at the University of Pennsylvania, where she first joined the faculty in 1975. And she’s still in love with microscopic imaging, specifically of muscles, both for the beauty of these images to which she has devoted her career, and for the secrets that these sneak-peeks into biology’s building blocks reveal.

It’s a love she has shared with countless students and researchers over the years, and now one she will share with generations to come. Known for her investigation of the organelles which deliver calcium within muscle cells during activation, Franzini-Armstrong is closing her lab, and making available a selection from her archive of thousands of electron microscope images – encompassing every type of muscle in the body, from humans to invertebrates – through the open-source journal Qeios. “Comparative anatomy of muscle and all other systems is an essential foundation of molecular biology,” she explains. “I am hoping that the images will encourage scientists to explore new and unusual muscles.”

Toadfish tubules: Transverse tubules (T-tubules) are like a broadband-speed connection between the interior of a muscle cell and the exterior, making rapid ion exchanges when the muscle contracts. The extensive network of T-tubules seen here in the super-fast sonic muscle cells of the toadfish is typical of a fast muscle.

The idea was planted in 1964, when Franzini-Armstrong’s postdoctoral advisor, noted cell biologist Keith R. Porter, suggested that an album of muscle electron micrographs was worth publishing, she recalls. “About 50 years later I finally did it. I know that he is very pleased, wherever he is.”

Although Franzini-Armstrong has technically been retired for 16 years (as emeritus professor of Cell and Developmental Biology), she remained a member of the Pennsylvania Muscle Institute and never quite gave up her studies. But now at 84, she’s ready to officially leave the lab; as she puts it, “I feel entitled to sit back and enjoy other people’s work.”

Across decades and thousands of images, Franzini-Armstrong still delights in each glimpse into the mysteries of muscular structure and function. She hopes others will look at her legacy and feel the same excitement: “The main motif through my work is that muscle is beautiful and although we think that we know all of it, surprises are around the corner.”

Two images show surface membrane of sarcoplasmic reticulum with a large number of calcium pump proteins, and a scallop’s muscle cell with the calcium pump proteins forming a semicrystalline arrangement

The patterns and shapes of calcium in muscle: The sarcoplasmic reticulum (SR) embedded in the membranes of muscle cells is essential to storing and pumping calcium ions when a muscle contracts. At left, the surface membrane of SR from a rabbit shows a large number of calcium pump proteins. The dots are the extensions of individual molecules from the cytoplasm. At right, in a scallop’s muscle cell, the calcium pump proteins form a semicrystalline arrangement. As a result, the SR components form a tubular shape.
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