December 26, 1967

Dr. Richard Bronson

2TT Avenue C

Apartment 6D

New York, New York 10009

Dear Dr. Bronson:

My trip to New York last October was followed by an extended trip, and

this is the first opportunity I have had to reply to your letter of
October 28.

I was indeed referring to Gurdon's work, and am sorry about the incorrect
reference to skin as the source of somatic nuclei. I don't know if this
originated in my own loese talk, or was some other misunderstanding between
me and the reporte®. This point hardly alters the principle in question.

There is a quantitative discrepancy between Gurdon's work and the investi-
gators who have used rana, but there is no actual conflict of observation,
and none of my colleagues seems to seriously question the validity of
Gurdon's reports. Gurdon has pretty well validdted his technique by the
use of genetic markera, and other ways of excluding the partipation of the
radiated nuclei from the development of the amphibian. Again, from the
point of view of the use of renucleation for vegetative propagation, it

is hardly very important whetkkr the original egg nucleus has been com-

pletely destroyed, provided the genetic make-up of the progeny is controlled
by the new nucleus.

The closest thing to this line of work in a mammalian system at the present
time is being done by Dr. B. Mintz in Philadelphia. I have heard several
rumors that enucleation has actually been successfully accomplished, although

there are still zsome loopholes in the data and renucleated mammalian eggs
have yet to be reared to term.

I do not have a manuscript of my talk, which was given mainly extemporary ,
but I can and do send you some brief articles that cover the same ground.

Sincerely yours,

Joshua Lederberg
Professor of Genetics

asvay ¢|