BSD News

Newly discovered fossils upend theory of vertebrate origin

BY ALISON CALDWELL, PHD

Paleontologists Michael Coates, PhD, left, and Rob Gess, PhD, conducting field research on the 360 millionyear-old Waterloo Farm black shales in South Africa. Anew study by researchers at the University of Chicago, the Canadian Museum of Nature and the Albany Museum challenges a long-held hypothesis that the blind, filter-feeding larvae of modern lampreys are a holdover from the distant past, resembling the ancestors of all living vertebrates, including ourselves. The new fossil discoveries indicate that ancient lamprey hatchlings more closely resembled modern adult lampreys, and were completely unlike their modern larvae counterparts.

“Modern lamprey larvae have been used as a model of the ancestral condition that gave rise to the vertebrate lineages,” said first author Tetsuto Miyashita, PhD, formerly a Chicago Fellow at UChicago and now a paleontologist at the Canadian Museum of Nature. “They seemed primitive enough, comparable to wormy invertebrates, and their qualities matched the preferred narrative of vertebrate ancestry. But we didn’t have evidence that such a rudimentary form goes all the way back to the beginning of vertebrate evolution.” Newly discovered fossils are changing the story. Connecting the dots between dozens of specimens, the research team realized that different stages of the ancient lamprey lifecycle had been preserved, allowing paleontologists to track their growth from hatchling to adult. On some of the smallest specimens, about the size of a fingernail, soft tissue preservation even shows the remains of a yolk sac, indicating that the fossil record had captured these lampreys shortly after hatching.

Crucially, these fossilized juveniles are quite unlike their modern counterparts (known as “ammocoetes”), and instead look more like modern adult lampreys, with large eyes and toothed sucker mouths. Most excitingly, this phenotype can be seen during the larval phase in multiple different species of ancient lamprey.

An artist’s rendering of a yolk-sac-carrying hatchling of the stem lamprey Priscomyzon riniensis.

“Remarkably, we’ve got enough specimens to reconstruct a trajectory from hatchling to adult in several independent lineages of early lampreys,” said Michael Coates, PhD, a professor in the Department of Organismal Biology and Anatomy, “and they each show the same pattern: the larval form was like a miniature adult.”

The researchers say that these results challenge the 150-year-old evolutionary narrative that modern lamprey larvae offer a glimpse of deep ancestral vertebrate conditions. By demonstrating that ancient lampreys never went through the same blind, filter-feeding stage seen in modern species, the researchers have upended this cherished ancestral model.

“We’ve basically removed lampreys from the position of the ancestral condition of vertebrates,” said Miyashita. “So now we need an alternative.”

After looking back at the fossil record, the team now believes that extinct armored fishes known as ostracoderms might instead represent better candidates for the root of the vertebrate family tree, whereas modern lamprey larvae are a more recent innovation.

The investigators believe that this is the sort of discovery that can rewrite textbooks. “Lampreys are not quite the swimming time capsules that we once thought they were,” said Coates. “They remain important and essential for understanding the deep history of vertebrate diversity, but we also need to recognize that they, too, have evolved and specialized in their own right.”

The study was published in March 2021 in Nature.

Why pregnancy may increase risk of organ transplant rejection

A University of Chicago study helps clarify why the immune system can tolerate a fetus during pregnancy, but later may be more likely to become sensitized to and reject an organ transplant.

During pregnancy, while the T cell response to a fetus becomes tolerant to allow for successful pregnancy, the part of the immune system that produces antibodies—known as the humoral response—becomes sensitized, the researchers found. This creates memory B cells that can contribute to organ rejection after a person has given birth, particularly if the transplanted organ, such as a kidney, is from a male partner.

In the study, the investigators tracked both the T cell response and humoral response of female mice after they received a transplanted heart from one of their offspring. They saw that the T cells did not react to the allograft, but the memory B cells did, producing antibodies against foreign antigens from the transplanted heart.

“One aspect of future research is to see if we can exploit this ability of pregnancy to tolerize T cells to have better acceptance not only in people who have been pregnant, but in everybody,” said Maria-Luisa Alegre, MD, PhD’93, Professor of Medicine, co-author of the study with Anita Chong, PhD, Professor of Surgery.

“Outside of pregnancy, people can get sensitized prior to transplantation in different ways, from disease or environmental antigens,” she said. “Now we’re looking at how pregnancy can tolerize these memory T cells that are otherwise difficult to immunosuppress with current drugs.”

The study was published in January in the Journal of Clinical Investigation.

Even after long-term exposure, bionic touch does not remap the brain

In a cohort of three subjects whose amputated limbs had been replaced with neuromusculoskeletal prosthetic limbs, investigators found that even after a full year of using the devices, the participants’ subjective sensation never shifted to match the location of the touch sensors on their prosthetic devices. The stability of the touch sensations highlights the limits in the ability of the nervous system to adapt to different sensory input.

“You can’t tell during the implantation surgery which part of the nerve corresponds to what sensation, so the electrodes don’t always land in exactly the location in the nerve that would match the location of the sensors in the prosthetic hand,” said the lead author and developer of the neuromusculoskeletal prostheses, Max Ortiz Catalan, PhD, an associate professor of bionics at Chalmers University of Technology. Investigators hoped the sensation might shift over time. But despite being able to observe their hands while interacting with objects, none of the users ever reported that they felt the sensation in the correct location; rather the sensation persisted in the same area where it was originally felt. This study highlights the importance of knowing exactly where to place electrodes when implanting Sliman Bensmaia, PhD sensory arrays, as it appears unlikely that the brain is capable of making substantial adjustments in how it perceives that sensory input. “This means that you really have to get it right,” said senior author Sliman Bensmaia, PhD, James and Karen Frank Family Professor of Organismal Biology and Anatomy at the University of Chicago. “There are no do-overs here.”

The study was published in December 2020 in Cell Reports.

— Alison Caldwell, PhD

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P1 Sensor

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Study participants using the neuroprosthetic device shown on the left all reported little change in the location of the sensation provided by their device, feeling it in the middle finger, palm or base of the thumb rather than at the tip of the thumb, despite long-term, daily use.

Thirteen members of the University of Chicago Pritzker School of Medicine Class of 2021 were inducted into the Gold Humanism Honor Society in February. Nominated by their peers, these students exemplify compassionate patient care and serve as role models, mentors and leaders.

The honorees are: Nicholas Antos, AB’17, Abena AppahSampong, AB’16, Jillian Baranowski, Stephanie Bi, AB’16, Christopher Da Silva, Nicole Dussault, SM’20, Gena Lenti, Robert Nolan, Christianah Ogunleye, Nichole Smith, Katherine Tran, Jasmine Tzeggai and Annie Zhang.

Jasmine Tzeggai, MS4, was the student Leonard Tow Humanism in Medicine Award recipient. Keme Carter, MD, Associate Professor in the Department of Medicine, was the faculty recipient of the Leonard Tow Humanism in Medicine Award and gave the keynote address.

Carter is also the 2021 Arnold P. Gold Foundation Humanism in Medicine Award nominee.

Virtual induction of the GHHS Class of 2021. Not pictured: Gena Lenti.

Alpha Omega Alpha Honor Medical Society

Twenty University of Chicago Pritzker School of Medicine students were inducted into the Alpha Omega Alpha (AΩA) Honor Medical Society. The honor society recognizes fourth-year medical students for academic excellence, leadership, compassion and fairness.

Members of the AΩA Class of 2021 are: Tess Allan, Michael Andersen, SB’15, Stephanie Bi, AB’16, Jeffrey Bunker, PhD’18, David Cook, Nicole Dussault, SM’20, Phillip Hsu, PhD’18, Ryan Judd, Gena Lenti, Seán Lyne, Robert Nolan, Christianah Ogunleye, Mikhail Pakvasa, Emily Papazian, Ramya Parameswaran, PhD’18, Anastasia Piersa, Kellie Schueler, Nichole Smith, Jasmine Tzeggai and Benjamin Yang.

Each AΩA class recognizes alumni, faculty and housestaff with election to the Illinois Beta Chapter (University of Chicago). Alumni are elected based on leadership and accomplishments, and are not eligible until 10 years after graduation. Faculty are elected based on demonstrated commitment to scholarly excellence and medical education. Residents and fellows are elected based on achievement, promise and mentorship qualities.

The 2021 honorees are:

Alumnus: John Blair, MD’03, Assistant Professor, Department of Medicine.

Faculty: Kamala Gullapalli Cotts, MD, Associate Professor, Department of Medicine, and Sonia Oyola, MD, Assistant Professor, Department of Family Medicine.

Housestaff: Dany Accilien, MD, Chief Resident in emergency medicine; Shirlene Obuobi, MD’18, and Ben Vasquez, MD, internal medicine residents.

Aimee Crow, MD, pediatric hospitalist at Evanston Hospital, part of the NorthShore University HealthSystem, and senior clinician educator for the Pritzker School of Medicine, received the Volunteer Clinical Faculty Award, which recognizes a community physician who contributes with distinction to the education and training of medical students.

Members of the Alpha Omega Alpha Class of 2021 participate virtually in the induction ceremony.