A histochemical study of epithelial mucin in the chick chorioallantois.

Histochemical methods demonstrate the accumulation of two types of mucous inclusion in the allantoic epithelial cells of the chick embryo. One type of inclusion contains a sialomucin that is PAS-reactive, unstained by Alcian blue and other anionophilic dyes and is susceptible to digestion by Vibrio choleme neuraminidase. The second inclusion contains an apparent sulfomucin which is Alcianophilic at pH 1.0, unstained by anionophilic dyes after a methylation-demethylation sequence and resistant to testicular hyaluronidase. This sulfomucin exhibits PAS reactivity after desulfation procedures. Both types of mucus occur in individual cells and are normal components of the chorioallantois. Accumulation of the inclusions is enhanced by lowering the pH of the allantoic fluid or as a result of organ transplantation. Microscopic examination of chick chorioallantoic membrane (CAM) revealed the presence of abundant mucus-like material within and on the surface of the allantoic epithelial cells. It was also observed that transplantation of certain organs to the CAM apparently enhanced the accumulation of this mucus. An interest in the morphology and function of the intact and transplant-recipient CAM prompted a more extensive histochemical investigation of the allantoic mucus. The objective was to obtain additional information about the normal CAM as well as to be able to interpret the results of subsequent studies of organ transplantation. MATERIALS AND METHODS The material employed in this study consisted of samples of CAM from white leghorn chick embryos ranging in age from 7-18 days (Hamburger and Hamilton, '51), although 17-18 day CAM was most extensively used. Samples of CAM were fixed in either 10% neutral-buffered formalin (pH 7.0), Bouin's fluid or 10% formalin containing 0.5 % cetylpyridinium chloride. Following fixation, the samples were washed, dehydrated in graded ethanol and embedded in paraffin. Sectioned samples were stained in the following: ( 1 ) periodic acid Schiff (PAS) and colloidal iron-PAS (Mowry, '58); (2) aldeAM. J. ANAT., 121: 741-748. hyde fuchsin (Gomori, '50) (prepared with basic fuchsin, (2.1. 42500), with and without oxidation in Lugol's solution; (3) aldehyde fuchsin and Masson trichrome (Masson, '29) (acid fuchsin, C.I. 4285, Ponceau R, (2.1. 16150, light green SF, C.I. 42095); (4) 0.01% aqueous azure A, cert. no. NAz 17, adjusted to pH 2.0 and 4.2 with hydrochloric acid; (5) 0.1% Alcian blue 8 GX ((2.1. 74240) in 3% acetic acid (pH 2.5) or 0.5% Alcian blue in 0.1 N hydrochloric