1006
REYSS-BRION
which the inducing and responsive tissues can be easily separated and
can be obtained in quantities sufficient for biochemical studies. I chose
the chick embryo skin.
METHODS
The dorsal skin of chick embryos at the stage of feather-germ
differentiation, that is, around 7 days of incubation, is spread out on the
medium culture following the method of Wolff and Haffen,’ then it is
irradiated and cultured for 5 or 6 days. Under these conditions, the
dose of X-rays (60 kv and 8 ma) which suppressesthe differentiation of
the feather germs in 90% of the cases is 1000 R (Fig. 6).
The two components (dermis and epidermis) were separated by
trypsin, irradiated separately, and finally recombined.
RESULTS
In the control, after recombination of a normal epidermis with a
normal dermis, normal feather germs are obtained in 100% of the cases
‘Fig. 7). The same result is obtained with recombination of irradiated
epidermis with normal dermis, but only in 95% of the cases (Fig.8).
After recombination of a normal epidermis with an irradiated dermis,
the explant shows no signsof feather germs in61% of the cases (Fig. 9).
In 39% of the cases some are present, but they are very small,
Consequently it can be concluded that in thisinteractive system irradiation of the dermis {s responsible for the inhibited differentiation.
On the other hand, the epidermis is very little affected by X-rays.
The next step was to try to relate these observations with changes
in the metabolism of skin cells, Hence, the possible changes in the nucletc acids and protein synthesis were explored by autoradiographic
and biochemical techniques in collaboration with Y.. Kong and J. M.
Kirrmann.!
Autoradiographic Studies
Incorporation (10 to 100 pCi/cullture medium) of thymidine (CH;-T).
In the controls, there is a heavy incorporation of thymidine in dermal
cells at the site of feather germs. In the irradiated explants, 2 to 3 hr
after irradiation, cells are less heavily labeled thanin controls and are
randomly distributed. After 4 hr some recovery seemsto take place.
In both cases, only traces of the label were found in the epidermis,
(Fig. 10).
Incorporation (10 to 100 Ci/culture medium) of uridine (5-T).
Uridine is uniformly taken up by the epidermal and dermalcells, and
{
}
f
'
|
}
1
}
+