Notch signaling functions as a binary switch for the determination of glandular and luminal fates of endodermal epithelium during chicken stomach development.

During development of the chicken proventriculus (glandular stomach), gut endoderm differentiates into glandular and luminal epithelium. We found that Delta1-expressing cells, undifferentiated cells and Notch-activated cells colocalize within the endodermal epithelium during early gland formation. Inhibition of Notch signaling using Numb or dominant-negative form of Su(H) resulted in a luminal differentiation, while forced activation of Notch signaling promoted the specification of immature glandular cells, but prevented the subsequent differentiation and the invagination of the glands. These results suggest that Delta1-mediated Notch signaling among endodermal cells functions as a binary switch for determination of glandular and luminal fates, and regulates patterned differentiation of glands in the chicken proventriculus.

Early specification of intestinal epithelium in the chicken embryo: a study on the localization and regulation of CdxA expression.

CdxA, a chicken homeobox-containing gene related to caudal in Drosophila, has been implicated in the regionalization of endoderm. It is reported here that, in the development of the chicken embryo, CdxA expression appears in the endoderm at day 1.5 of development as bilateral bands on either side of the splanchnopleure which later contribute to intestinal epithelium. The CdxA-expressing area extends medially and caudally as formation of the gut tube progresses. It is also shown that the rostral limit of CdxA expression demarcates the boundary between stomach and duodenum after day 3 of development. CdxA is not expressed in digestive tract appendages which open into the intestine, such as pancreas, liver and allantois. Early restriction of CdxA expression in intestinal lineage suggests that the intestinal specification involving CdxA expression commences before the gut tube is formed. The expression of CdxA in epithelial-mesenchymal tissue recombinants suggests that mesenchymal influence regulating CdxA expression plays an important role in confirming the boundary between the stomach and intestine. Chronological change in the spatial distribution of CdxA transcripts and the results of tissue recombination experiments, together with precise fate maps of early endoderm and splanchnic mesoderm, lead to a model of mechanisms by which intestinal specification is brought about.

Lectin histochemical study of glycoconjugates in the chick embryo proventriculus.

A lectin histochemical study was performed to investigate the glycoconjugate saccharidic moieties of the lining and glandular epithelium of the chick embryo proventriculus from day 7 to hatching. The sugar residues D-galactose-(beta 1-->3)-N-acetyl-D-galactosamine, N-acetyl-D-glucosamine, alpha/beta-N-acetyl-D-galactosamine and alpha-D-mannose were present at the lining epithelium of the proventriculus from the 7th day onwards; alpha-D-fucosyl residues were never detected. The same sugar residues were detected in the cells of the deep glands from the 7th day; alpha-L-fucose appeared later. The sugar residues appeared in the cells of the superficial glands at different times during the development of the proventriculus. In comparison to that of the deep glands, the secretion of the superficial glands was characterized, by the absence of N-acetylgalactosamine and alpha-D-mannose. From day 20 onwards, the composition of the mucus released by the two types of glands was identical from a qualitative point of view. The histological and histochemical results showed that the superficial glands are well defined morphological structures and not "an artefact of contraction", as claimed by other authors.

Molecular characteristics of pepsinogen and pepsin from duck glandular stomach.

1. Two procedures were developed for the preparation of duck pepsinogen, an enzyme from the family of aspartic proteases (EC 3.4.23.1) and its zymogen. 2. The amino acid composition, sugar content and the partial N- and C-terminal sequences of both the enzyme and the zymogen were determined. These sequences are highly homologous with the terminal sequences of chicken pepsin(ogen). 3. Duck pepsinogen and pepsin are unlike other pepsin(ogen)s in being relatively stable in alkaline media: pepsinogen is inactivated at pH 12.1, pepsin at pH 9.6. 4. Duck pepsin is inhibited by diazoacetyl-D,L-norleucine methyl ester (DAN), 1,2-epoxy-3(p-nitrophe-noxy)propane (EPNP), pepstatin and a synthetic pepsin inhibitor Val-D-Leu-Pro-Phe-Phe-Val-D- Leu. The pH-optimum of duck pepsin determined in the presence of synthetic substrate is pH 4. 5. Duck pepsin has a marked milk-clotting activity whereas its proteolytic activity is lower than that of chicken pepsin. 6. The activation of duck pepsinogen is paralleled by two conformational changes. The activation half-life determined in the presence of a synthetic substrate at pH 2 and 14 degrees C is 20 sec.

[Cellular retinol-binding proteins of the mucous membrane of the intermediate zone of the glandular stomach in chickens]. / Kletochnye retinolsviazyvaiushchie belki slizistoi obolochki promezhutochnoi zony zhelezistogo zheludka kur.

The cellular retinol-binding proteins with the molecular weight of 14 and 53.5 kDa have been isolated from the intermediate zone mucosa cells of the glandular stomach in chickens. No substantial differences in the amino acid composition of the investigated proteins have been found. The possible functional role of the isolated cellular retinol-binding proteins is discussed.

[Retinol-binding glycolipoproteins in secretions of the intermediate zone of the chicken glandular stomach]. / Glikolipoproteiny sekreta promezhutochnoi zony zhelezistogo zheludka kur, sviazyvaiushchie retinol.

Glycolipoconjugates of mucin from the intermediate zone of the hen glandular stomach is shown to include at least 5 glycolipoprotein threads with equal molecular weight of about 10 kD but with different lipid content and amino acid composition. Retinol is bound only to 2-3 glycolipoproteins which contain the highest quantity of covalently bound lipids. The retinol-binding with mucin glycolipoprotein threads, probably, occurs like the lipid-lipid interaction; neutral carbohydrates do not participate in this process.

[Interaction of the retinol-cellular retinol-binding protein complex in the Golgi apparatus of mucosa cells from the chicken glandular stomach]. / Vzaimodeistvie kompleksa retinol-kletochnyi retinolsviazyvaiushchii belok s apparatom Gol'dzhi slizistykh kletok zhelezistogo zheludka kur.

A Golgi-rich fraction has been isolated from the chicken glandular stomach mucosa cells and characterized. Interaction of the [3H]retinol--cellular retinol-binding protein complex with Golgi-rich fraction is shown. The uptake process is specific and saturable. Free retinol does not penetrate to a Golgi-rich fraction. An assumption is advanced that retinol-binding protein is involved in the transport of retinol to various cell particles, in particular, to the Golgi apparatus.

[The role of vitamin A in the formation of extracellular structures of the chicken glandular stomach]. / Rol' vitamina A v obrazovanii vnekletochnykh struktur zhelezistogo zheludka tsypliat.

Main notions on the vitamin A function in the organism are considered. A new concept is formulated postulating the vitamin A role in the support of the structure and function of the Golgi complex of epithelial cells of glandular stomach mucosa of chickens.

[Histochemical characteristics of the epitheliocytes of the avian glandular stomach]. / Gistokhimicheskie osobennosti épiteliotsitov zhelezistogo zheludka ptits.

A complex histochemical investigation has been undertaken to study the epithelial lining of the glandular stomach in birds having various types of nutrition. The protective barrier of the avian stomach has been found to be characterized as a resistant (mucosal) barrier, with neutral glycoproteins, sialo- and sulphoglycoproteins as its components. Differences in histochemical properties of the epitheliocyte secretion have been described in birds with different types of nutrition. They are connected with various correlation of carbohydrates and proteins in the composition of the micromolecular glycoprotein complex. The data obtained are compared with those concerning the histochemical properties of the stomach in amphibia and reptiles which have the mucous membrane structure similar to that in the avian stomach.