Making the Most from Changes in Life

How is the brain built? This is the question that first captivated me as a student. Back in 1985, we knew that the brain contained progenitor cells, but we didn’t know whether all of these were equivalent or how progenitors produced the vast diversity of cells present in the mammalian brain. I looked with envy on invertebrate biologists, who used simple, translucent organisms to watch neural development unfold over a few hours. Wouldn’t it be great if I could take progenitor cells out of the brain and watch them develop in vitro? The challenges were significant—there was no culture medium that could maintain neuronal progenitors and no method that could continuously follow individual cells over days in culture. A series of life events enabled me to work these problems out with help from many amazing colleagues.“I was fortunate to be able to bootstrap-up and turn such little initial funding into a strong research program.”Sally in her first laboratory.View Large Image | View Hi-Res Image | Download PowerPoint SlideSally and Jeff on their wedding day.View Large Image | View Hi-Res Image | Download PowerPoint SlideOn our wedding day in April 1987, we received the news that my husband to be, Jeff Stern, was accepted into medical school in Miami. I was a post-doc with Tom Jessell at Columbia University at the time and suddenly had to find a new career direction in Florida. This transition brought about excitement but also trepidation; would I find a lab with interests overlapping mine in Miami in the next few months? Fortunately, I did. John Barrett, who worked on brain development, offered me a position and gave me the freedom to tackle any question that I was interested in with my fellowship from the Royal Society. I decided to advance my PhD work on cloning glial progenitor cells and to take on the challenge of defining more broadly the characteristics of brain progenitor cells at the single-cell level. But here came the challenge: how to get neuronal progenitors to divide in vitro?John Barrett had spent years developing culture media to maintain neurons from the embryonic forebrain. He devised an “N5” culture medium that created some of the most beautiful neuronal cultures I had ever seen, but it was unclear if it promoted any progenitor cell proliferation. I began plating single cells from the embryonic rat forebrain into Terasaki wells and found that, luckily, a unique N5-based medium that John had developed supported the proliferation of single progenitor cells derived from the central nervous system (CNS). Importantly, clear subpopulations emerged: some that produced small clones of a few neurons and others that generated large clones containing both neurons and glia. This was a very exciting result, as it indicated heterogeneity among progenitor populations in the CNS and the existence of common progenitors for neurons and glia. Notably, some cells had much greater potential to divide and differentiate into a variety of progeny than others. Building on the emerging idea that there may be stem cells present in the neural crest and developing my observations from the in vitro clonal culture, in a paper published in Nature in 1989, I proposed that the embryonic brain contains stem cells. The series of lucky events that led me to work with John contributed to the blossoming of the neural stem cell field and discoveries for neural therapies that were pioneered by companies such as Stem Cells, Inc.“This ripple effect is also one of the most beautiful aspects of science.”Jeff and I then faced another huge transition in location and careers in 1990. The medical school match results were in, and Jeff accepted an ophthalmology residency at Albany Medical College in upstate New York. We drove from Miami to Albany in a Volkswagen Rabbit with our 6-month-old baby. In yet another unplanned transition, I found myself relying again on the kindness of colleagues. Anne Messer and Harry Kimelberg welcomed me to Albany. There was no job opening, but Harry provided a 200-square-foot room with an incubator, biological safety cabinet, sink, and a couple of benches, and that is how my independent lab began. My start-up funding was a modest salary and just $10,000, but I was grateful for every cent. Fortunately, soon afterward I received a Kingenstein Foundation award and then my first R01 grant. I was able to hire a technician, Susan Goderie, and my first graduate student, Andy Davis. We had a lot of fun in that lab; Susan and I sang songs while working side by side in the hood together. We took on more outstanding students and thrived knowing there was much to learn and figure out together. I was fortunate to be able to bootstrap-up and turn such little initial funding into a strong research program. It was an at times nerve racking but ultimately rewarding journey, which would not have been possible without significant collegial support and the mentorship of Martin Raff during my PhD, who taught me to ask bold questions and take a high-risk, high-reward approach that fortunately paid off.In our new lab, we focused on following brain progenitor cells over time to learn how they give rise to different types of progeny. This required time-lapse analysis of individual clones, which proved incredibly challenging. Back then, time-lapse recording was limited to a couple of hours, while studying brain lineages required continuous recording for about a week. Not to mention, sophisticated incubator microscope stages were not available at that time. My husband, ever the lateral thinker, said that, since clones grew well in the incubator, why not put a microscope in the incubator and add a camera to follow the dividing cells? This was a brilliant idea, but how could we jury-rig the system we needed? We found an ancient inverted microscope, fitted it with a video camera and a broken sliver of a far-red filter to reduce phototoxicity, put it in the incubator, and began recording onto tape the division patterns of single cortical progenitor cells for up to 7 days. Because the mouse brain expanded so much during development, I imagined that we would see extremely large clones with complex division patterns. Remarkably, however, we found that murine CNS stem cells underwent repeated asymmetric divisions, producing lineage trees highly reminiscent of those described previously for C. elegans and Drosophila neural development. In fact, the pattern of divisions shown by some mouse forebrain progenitor cells could be overlaid exactly on published invertebrate lineage trees. I was so excited to discover that neural lineage trees were evolutionarily conserved. Moreover, neurons were produced before glia (the same order in which they arise in the mammalian brain), demonstrating that the differentiation timing is programmed within progenitor cells. Later, we showed that even the order of cortical neuron layer generation was temporally programmed in individual cells at very early stages of development. When we published this in 2006, I received several notes from people saying that our discoveries inspired them to work on the problem of encoding temporal developmental programs.“I had some of my best scientific ideas during the quiet with kids asleep in my arms.”Our own life events have a way of spilling over, creating unexpected opportunities and changes for other people as well. This ripple effect is also one of the most beautiful aspects of science. From the simple goal of watching single brain progenitor cells divide emerged foundational discoveries about the presence of neural stem cells and associated translation to regenerative therapies. The seemingly straightforward idea of sticking a microscope into an incubator pointed us to the intriguing problem of temporal encoding of brain progenitor behavior.As our research matured, the imperative became to translate this toward therapy development. To put ourselves in the driver’s seat for moving discoveries from the bench to the bedside, Jeff and I founded the Neural Stem Cell Institute to promote basic and translational research, started a company to manufacture reagents that improve stem cell culture, and, most recently, set up a retina therapeutic company to develop therapies for vision impairment. Along the journey we had three children, Rebecca, Samuel, and Joshua, and I learned a lot about the challenges of balancing home and work. My mantra is always family first, but I would also say I had some of my best scientific ideas during the quiet, with kids asleep in my arms.Sally and Jeff in present day at a fundraiser for the Northeastern Association of the Blind at Albany.View Large Image | View Hi-Res Image | Download PowerPoint SlideIn looking back, I see clearly that certain critical life events impacted my career trajectory and that the generosity of colleagues and timely funding were key to navigating through unanticipated changes. I hope the young scientists today can benefit from a similarly supportive environment. They need it more than ever, considering the immense pressures of finding a job and running a research lab in today’s funding circumstances. The burden is sometimes so great that young people who are passionate about science and want to make research their career are turning away. We need to foster young scientists by strengthening support networks and making funding for them more accessible and secure. We need to empower them to navigate the unpredictable waters of biological discovery with the freedom to change trajectory when surprising findings or unexpected life events intervene. Indeed, it is those surprises that create leaps forward in knowledge development—the “non-obvious” that is the cornerstone of innovation and patentability and the foundation of transformative medical advances.