Scanning electron microscopical observations on the differentiating mesonephros of the chick embryo

Chick embryos were staged according to the method of Hamburger and Hamilton [1951] and fixed. Cross sections through the cephalic fourth of the mesonephric ridges were examined by scanning electron microscopy. The steps in glomerular differentiation could be observed with ease. The first foot processes to appear in podocytes arose directly from the basal surface of the cell body. In a second step, lateral branches appeared and gave off secondary or even tertiary branches that interdigitated with those from neighbouring podocytes, following a pattern that was very similar to the one previously described by other authors in metanephric nephrons. Endothelial pores appeared in the glomerular capillaries at very early stages of the glomerular differentiation. The differentiation of the epithelium of proximal tubules was characterized by the growth of apical microvilli and of finger-like evaginations from the lateral membranes. At stages 20 and 21, the most differentiated glomeruli had only basal foot processes; only after stage 25 did the first generation nephrons reach full maturity. Because during this period the mesonephros is known to produce urine, our results indicate that nephrons start to function before they have completed their differentiation.     

Study of the glycoconjugates in the mesonephros of the chick embryo using peroxidase-conjugated lectin

The distribution of the sugar residues in glycoconjugates along the mesonephric nephron of chick embryo from the 4th day of incubation till hatching has been investigated, by means of six different horseradish peroxidase-labelled lectins. ConA and WGA showed an ubiquitous presence of alpha-D-mannose and N-acetyl-D-glucosamine along the nephrons. SBA was found to be a specific marker of the proximal tubule. PNA and LTA reacted only for a short time at some sites during the considered period of incubation. Sialic acid was detected at the glomerulus in the podocytes, capillary wall and, with a lesser extent, in the mesangial cells. Significant changes of the glycosylation pattern of the glycoconjugates during the period of mesonephric activity and the period of involution were seen.     

Histochemical detection of sugar residues in the chick embryo mesonephros with lectin-horseradish peroxidase conjugates

Summary Fragments of mesonephros were taken from chick embryos and studied from the 4th to the 21st day of incubation. A battery of seven different horseradish peroxidase-labelled lectins was used to study the distribution of carbohydrate residues in glycoconjugates along the mesonephric nephron during the period of excretory activity and the period of involution. ConA and WGA reacted at every site of the nephron thus showing the ubiquitous presence of -D-mannose andN-acetyl-d-glucosamine. SBA was a good marker of the proximal tubule. Other lectins, such as PNA and LTA, reacted only for a short time at some sites during the considered period of incubation. The presence of sialic acid was detected in the podocytes, capillary wall and mesangial cells. From the 10th-11th day of incubation changes were noted in the proximal tubule as shown by PNA reactivity. This may be significant as regards the exact stage of incubation during which the involution of mesonephros begins.     

Histochemical detection of sugar residues in the chick embryo mesonephros with lectin-horseradish peroxidase conjugates

Fragments of mesonephros were taken from chick embryos and studied from the 4th to the 21st day of incubation. A battery of seven different horseradish peroxidase-labelled lectins was used to study the distribution of carbohydrate residues in glycoconjugates along the mesonephric nephron during the period of excretory activity and the period of involution. ConA and WGA reacted at every site of the nephron thus showing the ubiquitous presence of alpha-D-mannose and N-acetyl-D-glucosamine. SBA was a good marker of the proximal tubule. Other lectins, such as PNA and LTA, reacted only for a short time at some sites during the considered period of incubation. The presence of sialic acid was detected in the podocytes, capillary wall and mesangial cells. From the 10th-11th day of incubation changes were noted in the proximal tubule as shown by PNA reactivity. This may be significant as regards the exact stage of incubation during which the involution of mesonephros begins.     

Changes in the protein spectrum of the chick embryo mesonephros and metanephros in the course of development

The protein spectra of two fractions (the soluble and the membrane fraction) of chick embryo kidney homogenates were isolated by electrophoresis on polyacrylamide gels with the aim of detecting the kidney differentiation process at the molecular level and, at the same time, of evaluating similarities in the construction of the mesonephros and metanephros at this level. Corresponding stages of the above two types of kidney were chosen for studying changes in protein structure during differentiation--i.e. the outset of differentiation (the 6-day mesonephros, the 11-day metanephros) and the stage of full maturity (the 14-day mesonephros, the 20-day metanephros). A total of 36 proteins was distinguished. The analysis of the protein spectra showed that the number of proteins changes but slightly during differentiation; the protein composition of the two types of kidney during differentiation altered by 20-35% of the total number of proteins; the similarity of the protein composition of the corresponding stages of mesonephros and metanephros, expressed as the proportion of the number of identical proteins, was greater than the mutual similarity of different developmental stages of the same type of kidney. The percentage of different proteins at corresponding stages of the kidneys varied from 5% to 23% of the total number of proteins detected.     

Fine mapping of tropoelastin-derived components in the aorta of developing chick embryo

Summary Affinity-purified antitropoelastin antibodies have been used to localize tropoelastin-derived components in aortas from chick embryos of different age by immunoelectron microscopy. Staining in the matrix is first noted at day 3 associated with irregular bundles of filaments resembling microfibrils, in the absence of amorphous elastin deposits. Amorphous material, which rapidly accumulates at later stages, is heavily labelled, while surrounding microfibrils are only poorly labelled. By contrast, a more intense staining of microfibrils persists in regions in which amorphous material is not morphologically evident. These observations indicate that the initial accumulation of elastin requires microfibrils, while the two components are not in close association in the subsequent growth of the amorphous core of the fibre. Intracellular staining is evident in the secretory apparatus of the cell and in peripheral large vesicles. Differentiated cells also show regions of close contact with elastic fibres in which immunological staining for elastin is very close to the cell membrane.     

Fine structure of the developing gastric epithelium of the chick

The fine structure of the developing gizzard of the chick embryo has been studied to define the sequence of events in cytodifferentiation of the epithelium and to look for morphological evidence of epithelio-mesenchymal interaction. During the fourth day of incubation epithelial cells begin to form mucous secretory granules, later massive glycogen deposits appear, and finally by day 8 numerous cell processes have formed. Tissue was prepared by a number of methods to stain material associated with cell surfaces. At the time induction is presumbably occurring such stainable material is abundant. Epithelial and mesenchymal tissue components when cultured transfilter show no inductive effects and stainable cell surface material is greatly reduced near the epithelium.     

Renin immunohistochemistry in the mesonephros and metanephros of the pig embryo

Summary The occurrence and distribution of renin was investigated in meso- and metanephric kidneys of pig embryos in various gestational stages. The immunohistochemical peroxidase-antiperoxidase-method (PAP) was used on paraffin sections after application of an antiserum against mouse renin which cross reacts with pig renin. Renin immunoreactivity was already found in the mesonephros of 21 day pig embryos (crown-rump(CR)-length 12 mm) with the strongest reaction in the media of the juxtaglomerular afferent arteriole. Efferent vessels, mesonephric arteries, and the aortic wall also contained scattered renin-positive cells. In the definitive kidney, renin was not detected prior to the 25 mm CR-length-stage. In 45 mm embryos, immunocytochemical staining was observed not only in the media of kidney arteries and arterioles, but also in proximal tubules after pinocytic absorption of filtered renin. TEM-studies revealed that the media of both the mesonephric and the developing metanephric arteries and arterioles contains epithelioid cells whose ultrastructure is very similar to that of renin-producing cells in the adult organ. The observed distribution of renin-producing cells along the entire renal arterial tree points to the possibility that the major function of the renin-angiotensin system in the fetal animal is to participate in the stabilization of renal perfusion pressure.