Washington State Magazine

Fall 2008


Fall 2008

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In This Issue...

Features

The Higher Costs of College :: When it comes to paying the tuition, creative savvy may be a Cougar characteristic. Some do the expected--sell blood at the plasma center in Pullman, offer themselves up for psychology studies on campus, and find jobs either at the university or at a local restaurant. Others, over history, have been even more creative. by Hannelore Sudermann

{ WEB EXCLUSIVE–Our Story: How I made both ends meet }

The End Is the Beginning - a photo essay :: A Chinese native who was born during the Cultural Revolution, Jian Yang '08 found his artistic self somewhere in between his home country and the United States. That understanding of the in-between is perhaps why, on a visit home after spending some time here in graduate school, he discovered a fascination for the disappearing tradition of rural Chinese opera. by Hannelore Sudermann :: photography by Jian Yang

To Err Is Human :: The older a woman is when she conceives, the more likely it is her eggs will have abnormal chromosomes. But beyond the fact of the biological clock, we often overlook a bigger story. Even with young mothers, chromosome abnormalities are the single most frequent cause of miscarriage and birth defects. Between 25 and 30 percent of all fertilized human eggs have the wrong number of chromosomes, a rate that seems peculiar to humans. by Cherie Winner

{ WEB EXCLUSIVE–Story: Why do good eggs go bad? }

Essay

The New Virtualism: Beijing, the 2008 Olympic Games, and a new style for world architecture. by David Wang

Panoramas

{ WEB EXCLUSIVE–Video: What plants see...Changes how they grow }

{ WEB EXCLUSIVE–Video: A new biofuel crop for Washington farmers? }

Departments

Tracking

Cover photo: Sophomore Sarah Williams is borrowing money and working several jobs to help pay for college. She also sells her handmade jewelry in Pullman and on the internet to raise money to cover her school supplies. Photograph by Zach Mazur.

Fall 2008
Web Exclusives

Why do good eggs go bad?

by Cherie Winner | © Washington State University

 In 2004, researchers at Mount Sinai School of Medicine in New York produced a line of mice with an intriguing mutation. The mice make a defective form of a protein called SMC1beta that binds to chromosomes during the crossing-over stage. Pat Hunt and Terry Hassold, on the lookout for anything that might be involved in damage to chromosomes in the eggs of older women, recognized a hot prospect.

SMC1beta is part of a complex, or cluster, of four proteins called cohesins. The complex holds the two strands of each chromosome together while they break and recombine with the strands of their partner chromosome. Hunt and Hassold envision the cohesin complex wrapping around the strands like a rubber band. It has to stay there until meiosis I ends, which in human females might be decades later. Could problems with SMC1beta lead to errors in crossing over—and to chromosome damage?

When their former post-doc Craig Hodges examined oocytes from mice that had the defective form of SMC1beta, he found major problems with the crossovers.

“It looks like they’re making the right number [of crossovers], but when we go to look at them to see if they’re functional, whoa! We don’t see them in the same places, and if we look over time, we see fewer and fewer and they get closer and closer to the ends [of the chromosomes] until they’re just gone,” says Hunt.

By the time the mice with mutant SMC1beta were six months old, 80 percent of the chromosomes in their developing eggs were no longer attached to their partners. The meiotic choreography had completely fallen apart.

Hunt thinks the defective SMC1beta allows the cohesin complex to slide to the ends of the chromosomes and fall off, like a loose rubber band, so the DNA strands drift apart. With those strands not hanging together, the partnered chromosomes are unable to stay lined up properly.

Hunt thinks something similar could happen as women age, even if they start with normal SMC1beta. Perhaps the cohesins that hold the chromosome strands together degrade over time. After all, they were first laid down when the woman was herself an embryo.

“If that was 40 years ago, are you working with 40-year-old proteins?” asks Hunt. Most proteins in the body get replaced over much shorter time frames. She and Hassold are now trying to determine whether SMC1beta gets damaged over time and whether failure to repair or replace it contributes to the high rate of chromosome abnormalities in older eggs.

“There are a lot of candidates you can think of for making the maternal age effect, but this is a no-brainer,” says Hassold. “It has the features you would predict a maternal age-dependent factor would have. It’s probably not the only one”—but it’s a good place to start.

Categories: Biological sciences | Tags: Chromosomes, Birth defects