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CLEMENT LAWRENCE MARKERT April ]], 1917-October ], 1999 BY GERALD M. KIDDER CLEMENT L. MARKERT DIED on October I, 1999, in Colorado Springs, Colorado, at the age of 82. He and his wife, Margaret, had been living there since his retirement from North Carolina State University in 1993. Markert was born in Las Animas, Colorado, and grew up in the area around Pueblo. He and Margaret returned to "their mountain" near Westcliffe, Colorado, each summer. It was in their beloved mountain wilderness that he was laid to rest. Margaretjoined him in death the following year. They are survived by three children: Alan, Robert, and Samantha (Betsy) Schreck. A MAN OF IDEALS AND ACTION Clement Markert was a man of ideals whose devotion to social causes was evident from early in his career. His father had been a steel worker, and the family had suffered dur- ~ng the great Depression, when the mines and steel mills were closing. This experience undoubtedly influenced the . . _~ . ~ ~ development of Markert's social conscience. Grateful for scholarships awarded for his academic achievements, he enrolled in the University of Colorado at Boulder to study biology. At the same time, however, he was concerned about events on the world stage, especially what he perceived to 121

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122 B I O G RA P H I C A L EMOIRS be the failure of capitalistic economies to meet the neecis of working-cIass people. He embraced socialism en cl even organized a communist group at the university. He was very soon presenter! with an opportunity to put his social icleals into more direct practice. Responding to the threat of fas- cist movements taking hoIcl in Europe in 193S, he inter- ruptec! his studies and, along with his college roommate, rocle freight trains to the East Coast, where the two men stowocl away on a merchant ship bouncl for France. From there they joiner! the famous Abraham Lincoin Brigacle, which was fighting the forces of Generalissimo Franco in Spain, hoping to prevent his toppling of the democratically electec! government. Markert later explainer! that he hac! been one of the few members of his combat unit to survive the Spanish Civil War (his roommate was one of the casual- ties). In an obituary for Markert in The New York Times (October 10, 1999) he was quoted as having saicl in a 1986 interview, "I felt the most concrete thing I couIcl clo at the time was to destroy fascism, en c! Spain was the battleground! on which to clo that." After the defeat of the anti-Franco forces Markert re- turned to the University of Colorado to complete his un- clergracluate studies. He was awarclecl a B.A. summa cum laucle in ~ 940. In that same year he married Margaret Rempfer, who was to be his partner for life. The couple movecl to California so that Markert couIcl clo graduate work at the University of California, Los Angeles, where he con- cluctec! research in vertebrate embryology, however, woric! events again intervened. The Unitecl States became involvecl in WorIcl War II, en cl Markert chose to reactivate his per- sonal fight against fascism. He took a master's degree in 1942 to terminate his graduate education en cl triecl to en- list in the U.S. Army. Not surprisingly, given the political climate of the time, his previous associations with American

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CLEMENT LAWRENCE MARKERT 123 en c! Spanish communists, who hac! also been fighting against Franco, macle him unacceptable for military service. In re- sponse to this setback he movecl to San Diego to serve as a clockworker until being acceptec! into the merchant ma- rine. He served out the war as a raclio operator on a ship supplying U.S. forces in the Pacific. When his war years were finally behinc! him, Markert enrollecl in the cloctoral program in biology at Johns Hopkins University, where he concluctecl research uncler the mentorship of one of the country's foremost clevelopmen- tal biologists at the time, Benjamin H. Willier. After earn- ing the doctorate in 1948 he completecl his research train- ing as a Merck-NRC postcloctoral fellow at the California Institute of Technology. There he specializecl in biochemi- cal genetics uncler the influence of George W. BeacIle, the foremost proponent of that emerging fielcI. A MAN OF INTEGRITY AND COURAGE Markert's first independent academic appointment was at the University of Michigan in Ann Arbor, where he ac- cepted an assistant professorship in the Zoology Depart- ment in 1950. He became the intellectual leacler of a group of junior faculty who were in tune with the recent advances in biochemistry en cl genetics that lecl in 1953 to Watson en c! Crick's publication of the structure of DNA. The Markert family, which by this time incluclecl all three chilciren, settlecl into the pleasant life of the Ann Arbor academic commu- nity, en c! it seemec! that Markert's earlier life as a social activist was a thing of the past. This notion was shattered in 1954 when Markert en cl two colleagues were called before a subcommittee of the House Un-American Activities Committee meeting in East Lansing, Michigan. The subcommittee, chaired by Michi- gan Representative Kit CIarcly, was manciatec! to identify

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124 B I O G RA P H I C A L EMOIRS and root out communists from academia. Those who were targeted by the committee were threatened with being ex- posed as communists unless they named their former asso- ciates who might be considered communists or sympathiz- ers. The three men declined to cooperate, refusing to name anyone. As a consequence all three were suspended from their positions with the university, which set up review com- mittees at various levels to examine their cases. Markert was the only one of the three who was reinstated. According to David Nanney, a departmental colleague of Markert's at the time,~~ ~ ~ ~ Markert survived the ordeal because of support from his academic colleagues, who were convinced of his personal integrity, as well as scientists elsewhere (including George Beadle) who were impressed with Markert's scien- tific acumen and wrote letters on his behalf. Markert would later relate this experience to his students to emphasize the importance of standing up for one's convictions, whether scientific or political, regardless of the cost. Years later the university invited the three men back to Ann Arbor to re- ceive an apology for the way they had been treated. The controversy surrounding Markert's youthful social- ist activism did not end there. In 1957 he applied for the position in developmental biology at Johns Hopkins that was being vacated by his retiring mentor, Professor Willier. When the search committee recommended Markert's ap- pointment, administrative resistance developed. Markert had made no secret of his past, indeed, he was proud of it! The impasse was resolved when, after interviewing Markert him- self, the president of the university, Milton Eisenhower (brother of the President), recommended Markert's appoint- ment as a full professor and threatened to resign if the appointment was not confirmed. Markert accepted the po- sition and remained at Hopkins until moving to Yale Uni- versity in 1965 to become chair of the Department of Biol-

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CLEMENT LAWRENCE MARKERT 125 ogy. Once again Markert took pains to ensure that YaTe's president at the time, Kingman Brewster, was fully aware of his past en cl his intention to remain involvecl in social causes. During the late 1960s Markert was an outspoken opponent of the government's continuing involvement in the Viet- nam conflict en cl took an active role in public protests. Other causes that receiver! his outspoken support incluclec! affirmative action to promote women in academia en cl the "Zero Population Growth" campaign (his car license plate for a time was ZPG). Through this entire advocacy, as al- ways, Margaret was by his sicle. IncleecI, Markert attributed much of his confidence cluring those clifficult times in Michi- gan to the knowlecige that his wife wouic! be able to cope with whatever hardship his political activism brought upon them. MOST NOTABLE SCIENTIFIC CONTRIBUTIONS Throughout his career Markert aimed high: He wan tell to tackle the big questions in biological science, questions like how genes control clevelopment en cl how the genome of an organism can be manipulated to bring about genetic improvement. In many cases answering such questions re- quirecl the clevelopment of new research techniques. His scientific contributions covered a wicle range from biochem- istry through clevelopmental en c! reproductive genetics. Markert was best known early in his career for eluciciat- ing the importance and structural basis of isozymes, mul- tiple molecular forms of enzymes. The stage was set for that work when in 1957 Markert en cl his University of Michigan colleague, Robert L. Hunter, combined enzyme histochem- istry with the starch gel electrophoresis technique newly clevelopecl by Oliver Smithies to show that there are more than 10 separable forms of esterases in mouse liver (Hunter en c! Markert, 1957~. Using different substrates or inhibitors

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126 B I O G RA P H I C A L EMOIRS in the histochemical staining reaction, they obtained evi- clence that the different esterase bancis in the gel were en- zymatically distinct. The same technique but using cliffer- ent histochemical reagents also revealer! multiple forms of other enzymes, demonstrating that this phenomenon is not limitecl to esterases. The investigators termed their stained gel, showing multiple bancis representing the same enzy- matic function, a zymogram. In a subsequent paper com- municatecl to Proceedings of the National Academy of Sci- ences by Benjamin Willier, Markert en c! Frecicly Mailer user! the zymogram technique to show that the number of mo- lecular forms of lactate clehycirogenase (LDH) in mamma- lian tissues is greater than hac! been appreciates! en c! pro- posecl the term isozyme to denote these forms (Markert en cl Mailer, 1959~. They also showocl that tissues cliffer in the number of LDH isozymes they contain en c! their rela- tive proportions. Most importantly, their ciata macle it clear that the isozyme patterns of embryonic tissues change through ontogeny until the tissue-appropriate aclult pattern is achieved, a phenomenon that was interpreted as indicating changes in gene expression relatecl to cell differentiation. This insight into the utility of isozyme studies for under- stancling clevelopmental mechanisms was to influence Markert's research for years to come. Mailer, a Dane who hac! been trainee! in veterinary medicine before joining Markert's lab (by then at Hopkins), later creclitecl the ex- citement of those clays with his decision to make research his career. Markert's insights into the importance of cliffer- ential gene activation cluring clevelopment proviclecl a new way of looking at abnormal clevelopment as well, en cl he was one of the first to point out that diseases such as cancer can be viewocl as cell differentiation gone awry (Markert, 1 968~. As important as it was, Markert en c! M011er's 1959 paper

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CLEMENT LAWRENCE MARKERT 127 left unexplained! the molecular basis of isozymes. There was little appreciation at the time of the existence of gene fami- lies, evolutionarily relatecl genes encocling proteins of simi- lar or overlapping function. Yet Markert en c! Mailer clic! offer that as one explanation, citing the multiplicity of genes encocling fetal en cl aclult hemoglobins. They also suggested that a single gene might somehow encocle an array of isozymes differing in "structural variations," a concept that seems to presage our current unclerstancling of alternative mRNA splicing en c! post-transTational protein mollification. It was several years later, through the efforts of Ettore AppelIa, an Italian postcloc, that the Markert laboratory finally came to a clear unclerstancling of the molecular basis of LDH isozymes. By treating the enzyme with denaturing agents it was Earned that LDH is a tetramer of two types of polypepticle chains (Appella and Markert, 1961~. Thus the multiple-gene hy- pothesis was partially correct: Two different LDH subunits, each encoclecl by a distinct gene, re-sort themselves in vari- ous tetrameric combinations to give rise to five different isozymes (Markert, ~ 963 ) . During the succeeding years Markert en cl his students en cl postclocs continual to stucly the molecular basis and biological significance of isozymes en cl showocl how the stucly of isozymes couIcl contribute to our unclerstancling of the biochemical variation that uncler- lies cell differentiation and evolution. The culmination of this work was the new perspective presented in a Science paper (Markert et al., 1975) entitled "Evolution of a Gene," coauthored! with former graduate students James B. Shaklee en cl Gregory S. Whitt. Markert took particular pricle in his role in eluciciating the isozyme concept, not least because this was a case of a clevelopmental biologist teaching some- thing about biochemistry to the biochemists. For several years he served as editor or coeditor of the multivolume

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128 B I O G RA P H I C A L EMOIRS series "Isozymes" that emanates! from the annual Interna- tional Congress on Isozymes. Markert's preclilection for tackling the big questions some- times causer! problems for the person in his laboratory who was taking the leacl on a project. For example, one iclea that was tested cluring Markert's Hopkins years was that the program of gene expression within a cell is clictatec! by the constellation of nuclear proteins interacting with its DNA. If so, then it was hypothesized that introducing nuclear proteins from another source shouic! reprogram a cell's ge- netic machinery. This was tested by injecting liver nuclear proteins into fertilized frog eggs with the expectation that the embryos wouic! clevelop characteristics of liver cells. In- steacl the embryos arrested their clevelopment, en cl little was Earned from the experiment despite exhaustive attempts to analyze the embryos using the techniques of the clay. Markert was later criticized for investing resources en cl stu- clent time in such a simple-minclecl approach to a very com- plex problem, but if the experiment hac! worker! at least partially, it wouIcl have been a major step forward. Shortly after moving to Yale, Markert's laboratory be- came involves! in a new research topic that was to have an impact at least as important as that of the isozyme concept. Yoshio Masui, a young scientist from Konan University in Japan, arrived at Yale in 1966 on sabbatical leave to study biochemical aspects of cell differentiation and clevelopment. Masui had become intrigued by Markert's view of develop- ment as emanating from clifferential gene activation en c! wan tell to contribute to the eluciciation of that concept. He began working on LDH isozymes in penguin embryos, char- acterizing their changing expression patterns cluring clevel- opment. After less than a year, however, Masui came to the conclusion that the complexity of regulation of even a single enzymatic function during development was too great to be

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CLEMENT LAWRENCE MARKERT 129 eTuciciatec! by the technology available in the ~ 960s. He wan tell a more tractable problem to work on. Markert en- couragecl him to choose a project of his own interest, one that he conic! continue working on after returning to Japan. Masui cleciclecl that to unclerstancl cell differentiation it wouic! be advantageous to stucly an unambiguous cell change inclucecl by a well-clefinecl external signal. Remembering the classical experiment by Heilbrunn et al. (1939) in which oocytes were inclucec! to be releaser! from frog ovaries treater! in vitro with a pituitary glancl suspension, Masui reasoned that this must be an example of a clevelopmental incluction evokes! by a hormone. He was impresser! that a hormone couIcl act clirectly on its target tissue in vitro. Furthermore, Masui realizecl that hormonal incluction of melotic matura- tion en c! ovulation of the frog oocyte conic! provicle a highly advantageous system for studying the control of cell cycle events: It wouIcl allow the investigator to use distinct stimuli to incluce oocyte maturation (response to the hormone) en cl egg activation (cleavage in response to fertilization), thus separating the signals that drive the cell cycle from G2 to M phase and from M to G! phase, respectively. He hoped in this way to develop a research program in nucleocyto- plasmic interactions that he couIcl continue in Japan, where research resources were not as plentiful at the time, taking advantage of the ability to obtain large numbers of synchro- nous frog oocytes for biochemical analysis. For his part Markert was enthusiastic about that line of investigation, because he hacl often musecl about the possibility of sup- pressing meiosis in oocytes as a route to parthenogenesis. Masui's proposer! experiments were seen as an early step along that roacI, since they couIcl reveal how meiosis is con- trolled (Masui, 2001~. In early 1967 Masui starter! research on oocyte matura-

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30 B I O G RA P H I C A L EMOIRS tion by repeating Heilbrunn's classical experiment using Ran a pipiens. His experiments eventually lecl him to con- clucle that pituitary gonadotropin acts on the follicle cells of the ovary to stimulate them to release a progesterone- like hormone that clirectly acts on the oocyte. Further work revealecl that progesterone couIcl have an effect only when it actec! from the outsicle of the oocyte or on the cell sur- face, leacling him to propose that the oocyte cytoplasm car- ries the hormonal signal to the oocyte nucleus to incluce the first meiotic division. To test this hypothesis Masui in- jectecl the cytoplasm of oocytes inclucecl to mature by proges- terone into immature oocytes en cl found that these oocytes were inclucec! to mature without hormone treatment. That was the now famous experiment that clemonstratecl the pres- ence of a cytoplasmic factor, which Masui en cl Markert callecl maturation promoting factor (MPF), that caused oocyte maturation by triggering meiosis (Masui and Markert, 1971~. Using the same bioassay it was shown that MPF appears before the oocyte enters M phase, but clecTines when the oocyte proceeds to G] phase after fertilization. Masui also clemonstratecl that maturing oocytes contain another fac- tor, namer! cytostatic factor (CSF), that is responsible for the arrest of oocyte meiosis until fertilization. The manu- script reporting these exciting results (Masui and Markert, 1971) was published shortly after Masui moved to the Uni- versity of Toronto, where he is still working. It was the first significant step in unclerstancling how cell division is con- trollecI. That work was follower! by research in other labora- tories studying cell cycle regulation in yeasts, where the power of genetics was used to identify specific molecules having the properties of MPF and CSF. Today we know that MPF, more generally known as M-phase promoting factor, is a complex of cyclin B2, a regulatory protein that is syn- thesizec! en c! then clestroyoc! in each cell cycle, en c! Crick, a

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CLEMENT LAWRENCE MARKERT 131 catalytic protein that promotes entry into M phase. CSF is a Mos protein-containing complex that acts to prevent cyclin B2 clegraciation, thus maintaining the cell in M phase (Duesbery en c! Van cle Woucle, 2002~. The importance of Masui and Markert's 1971 paper was recognized in 1992 with the awarding of the prestigious Gairciner Awarcl () to Masui along with Lelanc! Hartwell en cl Paul Nurse, two of the scientists whose work in yeasts hacl iclentifiecl genes involvecl in cell cycle regulation. In ~ 998 the Lasker Foundation () recognized the same three scientists with the Lasker Award, but in 2001, when the Nobel Prize was awarclec! for contributions to unclerstancling the cell cycle, the winners were Lelancl Hartwell, Paul Nurse, en cl Tim Hunt, the last of whom hacl cliscoverecl the cyclins in his work with rapidly dividing embryos. Many of Masui's stu- clents en cl colleagues, particularly those who hacl shared in the excitement of his discoveries while working alongsicle him in Markert's laboratory, were cleeply clisappointec! at his being omitted from receiving the ultimate science prize. In the final phase of his research career at Yale, Markert turner! the attention of his laboratory to early mammalian clevelopment, a fielcl that hacl laggecl behind other areas of developmental biology until techniques were developed to allow experimentation with embryos cleveloping outsicle the womb. He undertook an ambitious project that was ahead of its time for its sheer boIciness: the procluction of a ho- mozygous diploid mouse. His approach was to remove one pronucleus from a fertilizecl egg, a very clelicate procedure, en cl then suppress the first mitotic division to restore the cliploic! conclition in the remaining pronucleus. Markert saw homozygous diploidy as an indirect route to cloning, since the offspring of successive generations proclucecl in the same way would theoretically be identical. Homozygous diploid

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132 B I O G RA P H I C A L EMOIRS blastocysts were obtainer! by this procedure, but none sur- vivecl to term after transfer to foster mothers (Markert en cl Petters, 1977~. Soon afterward another team of researchers ciaimec! to have succeeclec! with the same procedure (Hoppe en cl IlImensee, 1977~. Those results have not been repli- catecI. The current view, basecl on a large bocly of ciata, is that clifferential epigenetic mollification of sperm en c! egg genomes preclucles normal post-blastocyst clevelopment when the embryonic genome is clerivecl from a single parent. Markert liver! just Tong enough to see mammalian cloning, now performed by nuclear transfer into enucleatecl oocytes, become a reality (Wilmut et al., 1997~. Markert en c! postcloc Robert Petters clic! succeec! with another technically clemancling experiment: the procluction of hexaparental chimeras, mice macle up of cells from three different embryos having different genotypes (Markert en c! Petters, 1978~. They then repeated the experiment with four different embryos, producing octaparental mice (Petters en c! Markert, 1980~. This result prover! that at least four embryonic stem cells of the early embryo give rise to the fetus. Pictures of those hexaparental mice are still featured in clevelopmental biology textbooks. At the same time, a graduate student in Markert's laboratory, Vijay Thadani, was showing that rat oocytes can be fertilized by sperm of other mammalian species if the sperm are injected! clirectly into the oocytes (Thadani, 1980~. This experiment demon- stratecl that fertilization can occur without the normal pro- cesses of sperm activation, penetration of the zone pellu- cida, and sperm-oocyte binding, processes that are sometimes defective in infertile men, it presaged the now widely used technique of intracytoplasmic sperm injection (ICSI) as a treatment for male infertility. Ever the adventurer, Markert was eager until the end of his active research career to tackle the most clifficult and.

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CLEMENT LAWRENCE MARKERT 133 as he saw it, the most important biological questions. After retiring from Yale he finished his career as Distinguished University Research Professor in Animal Science en cl Ge- netics at North Carolina State University. SERVICE TO SCIENCE Markert believer! that scientists have an obligation to clo their share of administrative work en cl to serve on volun- teer boards en cl committees for the goocl of the scientific enterprise. In aciclition to serving as chairman of the De- partment of Biology at Yale (1965-71) he was director of the Center for Reproductive Biology (1974-85~. He was man- aging editor of The Jo urn a] of Experimen tad Zoology ~ ~ 963- 85) en cl coeditor (with John G. Scancialios) of Developmen- ta] Genetics (1979-92~. He served terms as president of the American Institute of Biological Sciences ~966), American Society of Zoologists (1967), en cl the Society for Develop- mental Biology ~ ~ 973-74) . Agencies en cl institutions that benefited from Markert's advice as a board member included the Bermuda Biological Station ~959-83), Presiclent's Bio- meclical Research Panel (1975), American Cancer Society (1976-78), Bioscience Information Service (1976-81 ), La Jolla Cancer Research Fund (1977-86), National Research Coun- cil ~ ~ 979-83), lane Coffin Fund for Meclical Research ~ ~ 979- 87), American Academy of Arts en c! Sciences (1981-84), en c! the Fecleration of American Societies for Experimental Bi- ology (1987-93~. As a member of the National Academy of Sciences he server! on several committees en c! was elected! to the Acaclemy's governing board, the Council. MARKERT AS TEACHER AND MENTOR Markert was a superb teacher whose lectures were leg- endary among undergraduates. Like his research interests, his lectures emphasizer! the big questions. He taught a course

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34 B I O G RA P H I C A L EMOIRS at Yale entitles! "Biology of Reproduction" that covered, in aciclition to the important biological principles, hot-button issues of the time such as overpopulation en cl abortion rights. The course also presenter! cutting-ecige reproductive tech- nology, inclucling actual procluction of chimeric mice. Markert returned to Yale for several years after his mandatory retire- ment to give lectures in the course that he hac! pioneered. For many of us who trained with Clem Markert, our memories are as much about the culture of his laboratory as about the science that was clone. Graduate students even more so than postclocs were given free reign to choose their own research topics en cl to pursue them more or less incle- penclently, the only requirement being that any project neeclecl to fit within the broacl scope of Markert's research interests, which was certainly not clifficult. In the late 1960s, for example, research in the Markert laboratory ranger! from LDH isozymes in various species through maturation en cl fertilization of frog and mouse oocytes to ribosomal gene redundancy and the molecular biology of molluscan devel- opment. Given the inclepenclence with which graduate stu- dents pursued their research, Markert usually declined to alit! his name to their publications, he clicI, however, re- ceive explicit acknowlecigement for financial support of the work and his mentorship. Despite his heavy administrative responsibilities he was often available to talk with incliviclual trainees without prior appointment and, unless he was trav- eling, couIcl be expected to sit clown to a bag lunch with laboratory members on a tinily basis. In aciclition to science, the conversations often focused on history (the American and Russian revolutions, for example), politics (a topic on which Markert was never hesitant to share his views), en c! even religion. An avowed atheist, Markert nonetheless was knowlecigeable about en cl respected the beliefs of his train- ees en c! colleagues. Whether his trainees agrees! with him

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CLEMENT LAWRENCE MARKERT 135 or not they knew they were being mentorec! by a man of superior intellect en cl strong social convictions who was willing to put his life en cl career on the line for what he believecl in. That, most of all, was Markert's legacy. THIS MEMOIR COULD not have been compiled without the assistance of former students and colleagues of Clem Markert. I am especially indebted to Richard Elinson, Yoshio Masui, David Nanney, Robert Petters, George Seidel, Vijay Thadani, and Gregory Whitt for pro- viding documentation and commentaries pertaining to Markert's life and career. REFERENCES Appella, E., and C. L. Markert. 1961. Dissociation of lactate dehy- drogenase into subunits with guanidine hydrochloride. Biochem. Biophys. Res. Comm. 6:171-76. Duesbery, N. S., and G. F. Vande Woude. 2002. Developmental biol- ogy: an arresting activity. Nature 416:804-805. Heilbrunn, L.V., K. Daugherty, and K. M. Wilbur. 1939. Initiation of maturation in the frog egg. Physiol. Zool. 12:97-100. Hoppe, P. C., and K. Illmensee. 1977. Microsurgically produced homozygous-diploid uniparental mice. Proc. Natl. Acad. Sci. U. S. A 74:5657-61. Hunter, R. L., and C. L. Markert. 1957. Histochemical demonstra- tion of enzymes separated by zone electrophoresis in starch gels. Science 125:1294-95. Markert, C. L. 1963. Lactate dehydrogenase isozymes: Dissociation and recombination of subunits. Science 140:1329-30. Markert, C. L. 1968. Neoplasia: A disease of cell differentiation? Canc. Res. 28:1908-14. Markert, C. L., and F. M011er. 1959. Multiple forms of enzymes: tissue, ontogenetic, and species specific patterns. Proc. Natl. A cad. Sci. U. S. A. 45:753-63. Markert, C. L., and R. M. Petters. 1977. Homozygous mouse em- bryos produced by microsurgery. J. Exp. Zool. 201:295-302. Markert, C. L., and R. M. Petters. 1978. Manufactured hexaparental mice show that adults are derived from three embryonic cells. Science 202:56-58.

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136 B I O G RA P H I C A L EMOIRS Markert, C. L., T. B. Shaklee, and G. S. Whitt. 1975. Evolution of a gene. Multiple genes for LDH isozymes provide a model of the evolution of gene structure, function, and regulation. Science 189: 102- 14. Masui, Y. 2001. From oocyte maturation to the in vitro cell cycle: the history of discoveries of Maturation-Promoting Factor (MPF) and Cytostatic Factor (CSF). Differentiation 69:1-17. Masui, Y., and C. L. Markert. 1971. Cytoplasmic control of nuclear behavior during meiotic maturation of frog oocytes. 7. Exp. Zool. 177:129-45. McGrath, T., and D. Solter. 1984. Inability of mouse blastomere nuclei transferred to enucleated zygotes to support development in vitro. Science 226:1317-19. Petters, R. M., and C. L. Markert. 1980. Production and reproduc- tive performance of hexaparental and octaparental mice. 7. Hered. 71 :70-74. Thadani, V. M. 1980. A study of hetero-specific sperm-egg interac- tions in the rat, mouse, and deer mouse using in vitro fertiliza- tion and sperm injection. 7. Exp. Zool. 212:435-53. Wilmut, I., A. E. Schnieke, T. McWhir, A. T. Kind, and K. H. Campbell. 1997. Viable offspring derived from fetal and adult mammalian cells. Nature 385:810-13.

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CLEMENT LAWRENCE MARKERT SELECTED BIBLIOGRAPHY 1948 137 The effects of thyroxine and anti-thyroid compounds on the synthe- sis of pigment granules in chick melanoblasts cultured in vitro. Physiol. Zool. 21: 309-27. 1950 The effects of genetic changes on tyrosinase activity in Glomerella. Genetics 35: 60-75. 1956 With W. K. Silvers: The effects of genotype and cell environment on melanoblast differentiation in the house mouse. Genetics 41:429- 50. 1957 With R. L. Hunter: Histochemical demonstration of enzymes sepa- rated by zone electrophoresis in starch gels. Science 125:1294-95. 1959 With F. M011er: Multiple forms of enzymes: tissue, ontogenetic, and species specific patterns. Proc. Natl. Acad. Sci. U. S. A. 45:753-63. 1961 With E. Appella: Dissociation of lactate dehydrogenase into sub- units with guanidine hydrochloride. Biochem. Biophys. Res. Comm. 6:171-76. 1963 Lactate dehydrogenase isozymes: Dissociation and recombination of subunits. Science 140: 1329-30. 1965 With I. Faulhaber: Lactate dehydrogenase isozyme patterns of fish. J. Exp. Zool. 159:319-32.

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38 B I O G RA P H I C A L 1966 EMOIRS With W. J. Sladen: Stability of lactate dehydrogenase isozyme pat- terns in penguins. Nature 210: 948-49. 1968 With E. J. Massaro: Lactate dehydrogenase isozymes: dissociation and denaturation by dilution. Science 162:695-97. 1969 With R. S. Holmes: Immunochemical homologies among subunits of trout lactate dehydrogenase isozymes. Proc. Natl. Acad. Sci. U. S. A. 64:205-10. 1971 With H. Ursprung: Developmental Genetics. Englewood Cliffs, N. J .: Prentice-Hall. With Y. Masui: Cytoplasmic control of nuclear behavior during mei- otic maturation of frog oocytes. J. Exp. Zool. 177:129-45. 1975 With J. B. Shaklee and G. S. Whitt: Evolution of a gene. Multiple genes for LDH isozymes provide a model of the evolution of gene structure, function, and regulation. Science 189:102-14. 1977 With R. M. Petters: Homozygous mouse embryos produced by mi- crosurgery. J. Exp. Zool. 201 :295-302. 1978 With R. M. Petters: Manufactured hexaparental mice show that adults are derived from three embryonic cells. Science 202:56-58. 1979 With K. I. Yamamura and Z. I. Ogita: Epigenetic formation of lac- tate dehydrogenase isozymes in the house mouse, Mus musculus. J. Exp. Zool. 208:271-80. With G. L. Hammond and E. Wieben: Molecular signals for initiat- ing protein synthesis in organ hypertrophy. Proc. Natl. Acad. Sci. U. S. A. 76:2455-59.

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