François Jacob – The Rest of the Story
In the early 1960s, François Jacob made several trips to the U.S., where he met
Alexandra (in Boston) and Bill (in California).
Bill, a chemistry graduate student at
Caltech, recalls Jacob prowling the basement of the Church Laboratory. Jacob had
joined Sydney Brenner and Matt Meselson at the invitation of Max Delbrück, the “Pope”
of “The Phage Church.” Jacob’s goal was to convince Delbrück of the Operon Model.
Brenner and Meselson joined into the monthlong event, carrying out the experiments
that tested the messenger RNA hypothesis for gene expression induced by infection by
phage T4. Jacob kept talking, matching with his impeccable logic the intense critiques
by Delbrück of the science and the language. This essay tells our part of the rest of the
story, stretching out a half century from that famous time.
During the ‘60s, Bill became an active member of the sect known as “The Lambda
Mafia” within the Phage Church (Hershey, 1971).
At that time, Bill’s interests
intersected those of Jacob, Brenner and François Cuzin’s Replicon Model (Jacob et al.,
1963) as modified by René Thomas and Elizabeth Bertani (Thomas and Bertani, 1964).
Soon, however, Jacob went off in search of new challenges in biology, surfacing in the
early 1970s to study mammalian development using the laboratory mouse.
This
commitment assumed that mouse development could be studied using the power of
microbial genetics, a handmaiden of many of the early discoveries in molecular biology,
including the Operon Model.
The link to microbial genetics was suggested by the
demonstration by Roy Stevens and Barry Pierce that a teratocarcinoma could be
derived by transplantation of an early mouse embryo to an ectopic site (Pierce et al.,
1967).
Perhaps, thought Jacob optimistically, these multipotential tumors could be
cultured and steps in mammalian development then recapitulated in culture, perhaps
enabling the isolation of informative mutants (Nicolas et al., 1976). One member of The
Lambda Mafia, Mark Ptashne, has written an eloquent appreciation of the intellectual
influence of François Jacob (Ptashne, 2013). In Ptashne’s view, “Jacob’s mastery failed
him when he dropped bacteria to work on developmental gene regulation in mice
(teratomas). …the experimental manipulations with mice, their time frames, and so on
are so different from those he had mastered with bacteria that he had no feel for them.”
We shall discuss our interactions with Jacob and colleagues, after we joined their
explorations in 1975-6. In subsequent decades, the molecular genetic analysis of
mammalian biology caught up with Jacob’s optimistic vision, in part through the efforts
of those with whom he talked, often over lunch at a nearby café (Figure 1).
In his approach to the study of mammalian development, Jacob paid particular attention
to the hypothesis that cell surface specificities are key to developmental decisions such
as the determination of interior versus exterior epithelial layers of the compacted early
morula (Kemler et al., 1977). Success came first with observations
of the effects of
antisera on interactions between EC cells (Nicolas et al., 1981) and with the discovery
of the cell adhesion molecule, uvomorulin, which is involved in compaction of embryonic
cells (Hyafil et al., 1980). However, gaining genetic traction on a causative analysis of
developmental functions was elusive. Early efforts, in collaboration with Dorothea
Bennett and Karen Artzt, focused on the set of natural variants at the T/t locus of the
mouse. Although each of these variants contained recessive lethal determinants, an
association between them and cell surface antigens (Kemler et al., 1976) remained
undefined at a molecular level. The complexity of the locus, a nested set of inversions
spanning several megabasepairs, blocked this level of resolution. This gap between
mammalian and microbial genetics was a subject of discussion during our visits to
Jacob and colleagues over the early ‘80s. Then, the discovery of mutagen-induced
immunogenic variants by Thierry Boon and his colleagues did lead to genetic analysis
with EC cells.
Those experiments were begun at the Pasteur Institute, and
consultations with Jacob are acknowledged in Boon’s first report (Boon and Kellermann,
1977). This success presumably involves dominant action by the mutant allele at a
diploid locus, creating a rejection neoantigen. By contrast, to find a way to uncover
recessive mutations in nearly diploid EC cells, we explored whether strong co-dominant
transplantation antigenic determinants are expressed on such cells. This approach was
suggested by the success of our colleague Bob DeMars in uncovering recessive
mutations from heterozygous lymphoblastoid cells (Kavathas et al., 1980). With Jacob
and his colleagues Philip Avner, Hedwig Jakob, and Jean-Louis Guénet we did identify
such determinants, linked to the major histocompatibility locus. Jacob, Guénet, and Bill
entertained the possibility that homologous mitotic recombination could provide a route
to uncover recessive phenotypes in cultured diploid cells. Evidence for this process in
the mouse was found by Jacob and his colleages (Panthier et al., 1990). Our laboratory
has recently capitalized on the metacentric karyotype of the rat to demonstrate
conservative mitotic recombination in uncovering recessive mutant phenotypes (AmosLandgraf et al., 2007). However, in the ‘70s, introduction into the mouse germline of
recessive mutations selected in EC cells was blocked because these cells fail to
populate the mouse germline when injected into early embryos. Discussions with Jacob
then turned to considerations of how to efficiently mutagenize the mouse germline and
classically use the meiotic cycle to uncover recessive point mutations in the mouse.
Germline genetics of the mouse reached molecular resolution in the ‘80s and ‘90s from
the intersection of three avenues.
One was the creation of a comprehensive map
through the discovery of widespread polymorphisms for restriction enzyme sites
between the laboratory strains and the subspecies Mus spretus (Minty et al., 1983).
Jacob’s colleagues, Guénet and Avner, were leaders in creating this resource (Avner et
al., 1988). Second was the development of efficient point mutagenesis of the mouse
germline by ethylnitrosourea (Dove, 1987; Russell et al., 1979). This enabled the T/t
haplotype to be dissected by recessive point mutations (Justice and Bode, 1986;
Shedlovsky et al., 1986).
Finally, the development of gene targeting in cultured
mammalian cells (Doetschman et al., 1987; Thomas et al., 1986) was carried forward to
the mouse germline through embryonic stem (ES) cells that could populate the
germline. Thus, two decades were needed to provide the experimental resources with
which to test rigorously the hypothesis that drove François Jacob’s effort in mammalian
biology: that cell surface specificities drive embryonic determination. We have noted
that some of these resources were developed by colleagues with whom Jacob kept
talking.
Woven throughout our interactions with François Jacob was his respect for the power of
language. Although he became fluent in English, he insisted that his research meetings
(“reunions”) be conducted in French. When we joined these reunions, Alexandra was
relatively familiar with French but new to the science. Reciprocally, Bill was still learning
French at L’alliance Francaise, but had acquired some familiarity with the scientific
issues addressed by the group.
We sat next to each other; imagine our hushed
exchange after a seemingly important point had been made: “What did he say?” “What
did he mean?” Jacob’s insistence on French for the language of his reunions reflected
his appreciation of French culture. We embraced some of this culture when, upon
returning to Madison, we shared with Julian and Dotty Davies an abonnemont de
fromage from Sarah Rapkine’s Fromagerie.
As we continued to communicate with
Jacob and colleagues over the decades since 1976, during one visit Bill even found
himself dreaming in French! During one such visit, Jacob was struggling to express in
both French and English the evolutionary concept by which he understood how new
functions are created by joining together two old functions. With the help of Roger
Stanier, the bilingual twins “bricolage” and “tinkering” were born. Beyond honoring the
French language and finding the right bilingual synonyms, François Jacob’s respect for
the power of language has led us to enjoy his insights and humanity through his books:
The Possible & The Actual (1982); The Statue Within: An Autobiography (1988); The
Logic of Life (1993); and Of Flies, Mice and Men (1998). His election to the Academie
Francaise was an honor he treasured at least as much as any from his scientific
research.
Throughout the half-century that we knew François Jacob, his signal contributions to the
revolution in molecular biology were behind him. But he kept talking and his younger
colleagues helped to fill some of the experimental gaps that intervened between the
concepts and the available techniques in mammalian genetics and biology. The
magisterial books he wrote during this time will keep talking for him. We last saw
François Jacob in 2011, on the occasion of the symposium at the Pasteur Institute
honoring the fiftieth anniversary of the Operon Model. From a chair on the stage, he
reminded his multigeneration audience of a message from his 1998 book: honor the
power of “night science” as you struggle to support your “day science.”
Alexandra Shedlovsky, Research Professor Emerita
William Dove, George Streisinger Professor of Experimental Biology Emeritus
The McArdle Laboratory for Cancer Research
University of Wisconsin – Madison
Figure 1: La Plage, 1982. Left to right: Georges Cohen, François Jacob and Hedwig
Jakob. Photograph W. Dove.
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