1979 Embryology Course

Ruderman returned to the MBL in the summer of 1979 to teach the Embryology course again. That same year, researcher Tim Hunt lectured at the Embryology course. Hunt worked largely with protein translation in reticulocytes (immature red blood cells) at his lab in the UK. Ruderman went to Hunt with the work she and Rosenthal had conducted the previous summer, in particular, the idea that the protein switch seen in clam oocytes after fertilization must be translational. Hunt, according to Ruderman, immediately disagreed with the hypothesis and was thus recruited by Ruderman to be the skeptic of their research team as she, Hunt, and Rosenthal continued with their research. That summer, the three of them worked with clam oocytes and embryos and eventually proved Ruderman’s hypothesis that the change in protein synthesis in fertilized eggs is translational (Ruderman interview, 6/5).

In order to test her hypothesis, Ruderman and her colleagues first labeled the proteins found in clam oocytes and then labeled the proteins found in clam embryos. To label a protein, researchers expose cells to a mixture of radioactive labels which attach to particular proteins and can be found in screenings later. After labeling the proteins found in clam oocytes and embryos, the researchers compared them. In oocytes, they found high levels of proteins they named X, Y, and Z. But in clam embryos, they found very low levels of X, Y, and Z and instead found high levels of proteins A, B, and C. The experiment confirmed that clam oocytes and embryos were synthesizing different proteins (Rosenthal, 1980).

Ruderman, Hunt, and Rosenthal then wanted to know how the embryos were producing such different proteins from the oocyte. The researchers looked at the mRNA found in both specimens. The kind and number of mRNAs are good indicators of what kinds and how many proteins can be produced by the cell. They started with the premise that transcription, working at the maximal rate of a given cell, could not produce the number of different mRNAs necessary for the differentiated protein production in embryos. That meant that the mRNA used to produce the proteins in embryos had to exist in oocytes, but remain inactive (not translated by ribosomes and used to produce proteins) (Rosenthal, 1980).

The next step for the team was to determine why certain mRNAs were translated at different stages and what controlled that translation. They first looked at the utilization of different mRNA sets before and after fertilization and found that, indeed, different mRNAs were translated in clam oocytes versus clam embryos. However, that did not answer the question of what controlled the switch from the translation of one set of mRNAs to the other set. To attempt to answer that, the team used the differing sets of mRNA in cell-free systems (outside cells in a laboratory environment) to translate proteins. The researchers did that to determine if the mRNA found in oocytes or embryos were simply not translatable, i.e. turned off in some way that made them incapable of producing protein until a particular point. Ruderman, Hunt, and Rosenthal found that even in a cell free system, the mRNAs universally translated to produce proteins. That meant that the mRNA found in both embryos and oocytes were translatable and could be used to produce proteins, but were not being used that way in the cell (Rosenthal, 1980).

By the end of the summer of 1979, Ruderman, Hunt, and Rosenthal had confirmed that the transition of protein synthesis between clam oocytes and embryos was translational, but had yet to determine what controlled the differential protein synthesis (Rosenthal, 1980).

Suggested citation
Abboud, Alexis. 2015. "Cyclins at the MBL". MBL History Project digital exhibit. http://history.archives.mbl.edu/exploring/exhibits/cyclins-mbl
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What are Cyclins?

Early Work with Cyclins

Tim Hunt and His Discovery of Cyclin

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