668
H O N O R
B .
F E L L
A N D
L .
M .
R I N A L D I N I
(b) Isolated epidermis. One obvious question was whether the vitamin
acted directly on the epidermis of embryonic chicken skin or whether
its effect was mediated through the dermis.
McLoughlin (1961) showed clearly that the action was directly on
the epithelium. She separated the epidermis from the limb-buds of
5-day embryos by means of tryptic digestion, and grew the isolated
epithelium with and without added vitamin A. Controls in normal
medium formed a squamous pearl whereas the vitamin A-treated
epithelium developed into a mucus-secreting nodule of quite different
structure.
(c) Effect of vitamin A on uptake of labelled compounds by explants of
embryonic chicken skin. An attempt was made to learn something of the
biochemical changes that accompany this mucous metaplasia. Pelc
and Fell (1960) investigated this point by cultivating control and
vitamin A-treated explants of 13-day metatarsal skin in medium containing various radioactive amino acids or inorganic sulphate; the
uptake of these compounds was then studied by autoradiography.
Most ofthe observations were made during the first 3 days of cultivation,
in order to investigate the early effects of the vitamin.
Among the amino acids, there was no obvious difference between
the vitamin A-treated and control epidermis in the uptake of
1 4
C -
leucine and
3 5
S-methionine, but the uptake of
3 5
S-cystine was far
greater in the controls. This difference was probably correlated with
the inhibition of keratinization by the vitamin.
When the explants were treated with inorganic sulphate (
3 5
S 0 4 )
which is incorporated into acid mucopolysaccharides, the uptake in
the basal cells of the epidermis was almost the same whether vitamin
A was present or not, but in the superficial cells it was much greater in
the vitamin A-treated explants. From this it was concluded that the
normal epidermal cells are able to manufacture acid mucopolysaccharides, but that this process is arrested in the superficial layers by keratinization. Since vitamin A inhibits keratinization, the synthesis can continue at all levels of the epidermis in the presence of excess of the vitamin
At a later stage of cultivation, when the hypervitaminotic skin begins
to secrete mucus, the uptake of sulphate in the superficial cells is very
intense.
(d) Effect of vitamin A on epidermal fine structure. Recently, Fitton
Jackson and Fell (1963) have examined the effect of vitamin A on the
fine structure of explants of metatarsal skin from 12-day chick embryos.
After 7 days' cultivation in normal medium, the superficial cells
below the stratum corneum were engaged in keratin formation (Fig. 10)
and presented a very different appearance from those of sister explants
exposed to vitamin A. In the latter, the upper surface of the outermost
H O N O R
B .
F E L L
A N D
L .
M .
R I N A L D I N I
(b) Isolated epidermis. One obvious question was whether the vitamin
acted directly on the epidermis of embryonic chicken skin or whether
its effect was mediated through the dermis.
McLoughlin (1961) showed clearly that the action was directly on
the epithelium. She separated the epidermis from the limb-buds of
5-day embryos by means of tryptic digestion, and grew the isolated
epithelium with and without added vitamin A. Controls in normal
medium formed a squamous pearl whereas the vitamin A-treated
epithelium developed into a mucus-secreting nodule of quite different
structure.
(c) Effect of vitamin A on uptake of labelled compounds by explants of
embryonic chicken skin. An attempt was made to learn something of the
biochemical changes that accompany this mucous metaplasia. Pelc
and Fell (1960) investigated this point by cultivating control and
vitamin A-treated explants of 13-day metatarsal skin in medium containing various radioactive amino acids or inorganic sulphate; the
uptake of these compounds was then studied by autoradiography.
Most ofthe observations were made during the first 3 days of cultivation,
in order to investigate the early effects of the vitamin.
Among the amino acids, there was no obvious difference between
the vitamin A-treated and control epidermis in the uptake of
1 4
C -
leucine and
3 5
S-methionine, but the uptake of
3 5
S-cystine was far
greater in the controls. This difference was probably correlated with
the inhibition of keratinization by the vitamin.
When the explants were treated with inorganic sulphate (
3 5
S 0 4 )
which is incorporated into acid mucopolysaccharides, the uptake in
the basal cells of the epidermis was almost the same whether vitamin
A was present or not, but in the superficial cells it was much greater in
the vitamin A-treated explants. From this it was concluded that the
normal epidermal cells are able to manufacture acid mucopolysaccharides, but that this process is arrested in the superficial layers by keratinization. Since vitamin A inhibits keratinization, the synthesis can continue at all levels of the epidermis in the presence of excess of the vitamin
At a later stage of cultivation, when the hypervitaminotic skin begins
to secrete mucus, the uptake of sulphate in the superficial cells is very
intense.
(d) Effect of vitamin A on epidermal fine structure. Recently, Fitton
Jackson and Fell (1963) have examined the effect of vitamin A on the
fine structure of explants of metatarsal skin from 12-day chick embryos.
After 7 days' cultivation in normal medium, the superficial cells
below the stratum corneum were engaged in keratin formation (Fig. 10)
and presented a very different appearance from those of sister explants
exposed to vitamin A. In the latter, the upper surface of the outermost