Effect of retinoids on the differentiation of chick embryo metatarsal skin explants

Either chick embryo dermis or retinoid-treated mouse dermis can initiate glandular morphogenesis from mammalian epidermal tissue

Excess retinoids can cause developing mouse vibrissa follicles to be transformed into mucous glands in organ culture. The objective was to test the hypothesis that retinoids act in this system by altering morphogenetic properties of the dermis. After inititation by retinoic acid (RA) in organ culture, glands were shown to develop further in embryonic skin grafted to the chick chorioallantoic membrane (CAM). Recombinants of 12.5 day mouse epidermis with untreated or RA-treated mouse or chick dermis were then grafted to CAM for 7 days. For homospecific recombinants, 13.5 day mouse dermis originated from 11.5 day skin cultured for 2 days, with or without 5.2 microgram/ml RA. For heterospecific recombinants, 12 day dermis came from chick embryos, previously injected with 250 microgram RA. Glands were absent from the homospecific recombinants including untreated mouse dermis, but appeared in 26% of those with RA-treated dermis. Among heterospecific recombinants, 75% of those with RA-treated chick dermis and 29% of those with untreated dermis had glands. Untreated 10-12 day chick skin contained two forms of endogenous vitamin A, retinol (4.5 microgram/g protein) and dehydroretinol (3.7 microgram/g protein), while 13-14 day mouse skin contained only retinol (1.8 microgram/g protein), as shown by high performance liquid chromatography. RA injection increased retinol and dehydroretinol in chick skin, while RA was undetectable. Thus RA can act through mouse dermis to form epithelial glands and through chick dermis to increase the incidence of glands. The glands in recombinants with untreated chick dermis may result from the higher levels of endogenous retinoids in chick skin, compared with mouse skin.

The in vivo inhibition of mouse brain protein kinase-C by retinoic acid

The intracisternal injection of either all-trans-retinoic acid or [alpha]-difluoromethylornithine (DFMO) into the brain of 9-day-old mice blocked (greater than 90%) phorbol ester-induced ornithine decarboxylase (ODC, EC 4.1.1.17) activity in a concentration-dependent fashion; this inhibition was not evident with the use of the biologically impotent furyl analog of retinoic acid. In a similar manner, retinoic acid reduced the soluble protein kinase-C (PK-C) activity by 60% as well as total EGTA-sensitive kinase activity (66%) associated with the plasma membrane. Sixty-six percent of the retinoic acid-induced loss of PK-C activity in the soluble fraction could be accounted for by the translocation of PK-C to the plasma membrane as measured by the specific binding of 12-O-[3H]tetradecanylphorbol-13-acetate (TPA). DFMO and furyl-retinoic acid were not effective in altering PK-C activity or TPA binding to PK-C. In the presence of retinoic acid, however, there was a 2.3-fold increase in specific [3H]TPA binding in the plasma membrane fraction, which was 3.4-fold greater than that lost from the cytosol. Because retinoids do not directly affect TPA binding to PK-C, the data suggest that (i) the presence of retinoic acid results in the exposure of heretofore cryptic TPA-binding sites in the membrane, where this binding is most likely related to the alteration of membrane structure and (ii) de novo ODC induction is not required for retinoid-dependent inhibition of PK-C, although the TPA induction of PK-C appears to be necessary with regard to ODC induction.

Structure-activity relationships of retinoids in the morphogenesis of cutaneous appendages in the chick embryo

We have evaluated the efficacy of 13 analogues of retinoic acid (retinoids) in producing in vivo feathers on the normally scaly foot integument (ptilopody) of the chick embryo. The retinoids were dissolved in dimethylsulfoxide and injected at doses from 1.25-250 micrograms into the amniotic cavity of embryos of 10 days of incubation. The results showed that the production of ptilopody requires specific retinoids, namely, those incorporating a free trans carboxylic end group. Indeed, the esterification of this acid end group (retinoid ethyl ester) leads to a delay in the effect of the product. Its substitution by an alcohol (retinol) or an aldehyde group (retinal), or its isomerization, leads to inactive products. The esterification by acetic acid of the alcohol terminal group of retinol leads to a moderately active compound (retinyl acetate). By contrast, modifications of the ring do not interfere with the efficacy of the retinoid, and modifications of the side chain by addition of one or two supplementary rings lead to an increase of the activity.

Structure-activity relationship of retinoids in fetal rat bone cultures

The structure-activity relationship of 29 retinoids was investigated in fetal rat bone organ cultures. Retinoids induced the release of proteoglycan followed by cartilage tissue breakdown. In this study the loss of RNA was used as a parameter for cartilage resorption. During 6 days of incubation RNA decreased up to 80% in presence of active retinoids. Thus the ED40 was determined from dose-response curves of the various retinoids. The new compounds, called arotinoids, which contained the retinoic acid carbon skeleton in a fixed cisoid geometric conformation, were up to 200 times more active than all-trans-beta-retinoic acid. The most active compound contained a tetramethylated tetralin ring and a second aromatic ring in the side chain. Several lines of evidence indicated that the carboxylic acid end group was essential for the activity of retinoids in fetal bone cultures. The new, highly active retinoids described here might be an excellent tool to investigate whether the retinoid action is mediated by specific cellular retinoid binding proteins.