Vascularization and glomerular ultrastructure in the pig mesonephros

Chain-Like Structures of Biogenic and Nonbiogenic Magnetic Nanoparticles in Vascular Tissues

In this paper, slices of organs from various organisms (animals, plants, fungi) were investigated by using atomic force microscopy and magnetic force microscopy to identify common features of localization of both biogenic and nonbiogenic magnetic nanoparticles. It was revealed that both biogenic and nonbiogenic magnetic nanoparticles are localized in the form of chains of separate nanoparticles or chains of conglomerates of nanoparticles in the walls of the capillaries of animals and the walls of the conducting tissue of plants and fungi. Both biogenic and nonbiogenic magnetic nanoparticles are embedded as a part of the transport system in multicellular organisms. In connection with this, a new idea of the function of biogenic magnetic nanoparticles is discussed, that the chains of biogenic magnetic nanoparticles and chains of conglomerates of biogenic magnetic nanoparticles represent ferrimagnetic organelles of a specific purpose. Besides, magnetic dipole-dipole interaction of biogenic magnetic nanoparticles with magnetically labeled drugs or contrast agents for magnetic resonance imaging should be considered when designing the drug delivery and other medical systems because biogenic magnetic nanoparticles in capillary walls will serve as the trapping centers for the artificial magnetic nanoparticles. The aggregates of both artificial and biogenic magnetic nanoparticles can be formed, contributing to the risk of vascular occlusion. Bioelectromagnetics. 43:119-143, 2022. © 2021 Bioelectromagnetics Society.

Understanding normal and abnormal development of the Wolffian/epididymal duct by using transgenic mice

The development of the Wolffian/epididymal duct is crucial for proper function and, therefore, male fertility. The development of the epididymis is complex; the initial stages form as a transient embryonic kidney; then the mesonephros is formed, which in turn undergoes extensive morphogenesis under the influence of androgens and growth factors. Thus, understanding of its full development requires a wide and multidisciplinary view. This review focuses on mouse models that display abnormalities of the Wolffian duct and mesonephric development, the importance of these mouse models toward understanding male reproductive tract development, and how these models contribute to our understanding of clinical abnormalities in humans such as congenital anomalies of the kidney and urinary tract (CAKUT).

Infrahepatic inferior caval and azygos vein formation in mammals with different degrees of mesonephric development

Controversies regarding the development of the mammalian infrahepatic inferior caval and azygos veins arise from using topography rather than developmental origin as criteria to define venous systems and centre on veins that surround the mesonephros. We compared caudal-vein development in man with that in rodents and pigs (rudimentary and extensive mesonephric development, respectively), and used Amira 3D reconstruction and Cinema 4D-remodelling software for visualisation. The caudal cardinal veins (CCVs) were the only contributors to the inferior caval (IVC) and azygos veins. Development was comparable if temporary vessels that drain the large porcine mesonephros were taken into account. The topography of the CCVs changed concomitant with expansion of adjacent organs (lungs, meso- and metanephroi). The iliac veins arose by gradual extension of the CCVs into the caudal body region. Irrespective of the degree of mesonephric development, the infrarenal part of the IVC developed from the right CCV and the renal part from vascular sprouts of the CCVs in the mesonephros that formed 'subcardinal' veins. The azygos venous system developed from the cranial remnants of the CCVs. Temporary venous collaterals in and around the thoracic sympathetic trunk were interpreted as 'footprints' of the dorsolateral-to-ventromedial change in the local course of the intersegmental and caudal cardinal veins relative to the sympathetic trunk. Interspecies differences in timing of the same events in IVC and azygos-vein development appear to allow for proper joining of conduits for caudal venous return, whereas local changes in topography appear to accommodate efficient venous perfusion. These findings demonstrate that new systems, such as the 'supracardinal' veins, are not necessary to account for changes in the course of the main venous conduits of the embryo.

Development of the human infrahepatic inferior caval and azygos venous systems

Differences in opinion regarding the development of the infrahepatic inferior caval and azygos venous systems in mammals centre on the contributions of 'caudal cardinal', 'subcardinal', 'supracardinal', 'medial and lateral sympathetic line' and 'sacrocardinal' veins. The disagreements appear to arise from the use of topographical position rather than developmental origin as criterion to define separate venous systems. We reinvestigated the issue in a closely spaced series of human embryos between 4 and 10 weeks of development. Structures were visualized with the Amira(®) reconstruction and Cinema4D(®) remodelling software. The vertebral level and neighbouring structures were used as topographic landmarks. The main results were that the caudal cardinal veins extended caudally from the common cardinal vein between CS11 and CS15, followed by the development of the subcardinal veins as a plexus sprouting ventrally from the caudal cardinal veins. The caudal cardinal veins adapted their course from lateral to medial relative to the laterally expanding lungs, adrenal glands, definitive kidneys, sympathetic trunk and umbilical arteries between CS15 and CS18, and then became interrupted in the part overlaying the regressing mesonephroi (Th12-L3). The caudal part of the left caudal cardinal vein then also regressed. The infrarenal part of the inferior caval vein originated from the right caudal cardinal vein, while the renal part originated from subcardinal veins. The azygos veins developed from the remaining cranial part of the caudal cardinal veins. Our data show that all parts of the inferior caval and azygos venous systems developed directly from the caudal cardinal veins or from a plexus sprouting from these veins.

Expression and localization of angiogenic growth factors in developing porcine mesonephric glomeruli

The development and growth of renal glomeruli is regulated by specific angiogenic growth factors, including vascular endothelial growth factor (VEGF) and the angiopoietins (ANGPT1 and ANGPT2). The expression of these factors has already been studied during metanephric glomerulogenesis, but it remains to be elucidated during the development of the embryonic mesonephros, which can function as an interesting model for glomerular development and senescence. In this study, the presence of the angiogenic growth factors was studied in developing porcine mesonephroi, using IHC and real-time RT-qPCR on laser capture microdissected glomeruli. In addition, mesonephric glomerular growth was measured by using stereological methods. ANGPT2 remained upregulated during maturation of glomeruli, which may be explained by the continuous growth of the glomeruli, as observed by stereological examination. The mRNA for VEGFA was expressed in early developing and in maturing glomeruli. The VEGF receptor VEGFR1 was stably expressed during the whole lifespan of mesonephric glomeruli, whereas VEGFR2 mRNA was only upregulated in early glomerulogenesis, suggesting that VEGFR2 is important for the vascular growth but that VEGFR1 is important for the maintenance of endothelial fenestrations.

Differential regulation of two sets of mesonephric tubules by WT-1

Mammalian renal development undergoes two transient stages, the pronephros and the mesonephros. While the regulation of metanephric differentiation has received considerable attention, very little is known about the mode of differentiation of the mesonephros and its regulation. We have followed mesonephric differentiation to unravel the developmental mechanisms and fates of mesonephric tubules by whole-mount immunohistology using antibodies to laminin, brush border epitopes, cytokeratin-8/18, p75 neurotrophin receptor and some other renal antigens as markers. In rat and mouse embryos, two distinct sets of tubules were observed throughout mesonephric development. Four to six pairs of cranial mesonephric tubules developed as outgrowths from the Wolffian duct. The majority of tubules were caudal tubules which never fused with the Wolffian and differentiated similarly to metanephric nephrons. The murine mesonephric tubules degenerate by apoptosis, except in males where the cranial tubules become the epididymal ducts. These developmental differences between the cranial and caudal sets of tubules suggested different regulatory systems for each. Targeted disruption of the Wilms' tumour gene product, WT-1, results in renal aplasia, and a reduction in the number of mesonephric tubules (Kreidberg, J. A., Sariola, H., Loring, J., Maeda, M., Pelletier, J., Housman, D. and Jaenisch, R. (1993). Cell 74, 679–691). We therefore analysed more closely mesonephric differentiation in WT-1-deficient mice, and showed that they only develop the cranial mesonephric tubules but not the caudal ones. Thus, WT-1 appears to regulate only the development of the caudal mesonephric tubules that conceivably are formed from mesenchymal cells like the metanephric tubules. WT-1 therefore seems to be necessary for the mesenchyme to epithelium transitions at different stages of nephrogenesis.

Afferent portal venous system in the mesonephros and metanephros of chick embryos: development and degeneration

BACKGROUND

In the chick embryo, both mesonephros and metanephros have a renal portal system. The classical literature gives uncertain answers about the development and degeneration of the meso- and metanephric portal venous system. Some mesonephric vessels present angiogenic processes to colonize the metanephros, while others show signs of degeneration and disappear together with the mesonephros. The adult avian kidney has a conspicuously placed valve, the renal portal valve. The development of this functionally important renal portal valve has not yet been studied in detail.

METHODS

Scanning electron microscopy of vascular corrosion casts has been used in this study. Strong mesonephric degeneration as well as metanephric growth and maturation occur in the developmental stages selected for this investigation (7.5, 9, 11, 14, and 21 days of incubation).

RESULTS

The mesonephric afferent venous system in the chick embryo is supplied by two vessels, the posterior and the anterior mesonephric portal veins. The posterior mesonephric portal veins show a similar pattern to the anuran (amphibian) kidney. The anterior mesonephric portal vein has not previously been described. Constrictions were found in this vessel, a probable sign of subsequent degeneration. The metanephric afferent venous system is also supplied by two vessels: the caudal and cranial metanephric portal veins. The caudal metanephric portal vein is derived from the postcardinal vein. The cranial metanephric portal vein grows independently throughout the development of the mesonephric vascular system. It is connected to the vertebral venous sinus already at the beginning of its development. The renal portal valve first appears as a capillary network that communicates with the developing afferent and efferent metanephric venous systems. This capillary network later develops to a venous valve. The metanephric afferent venous system shows typical angiogenic signs in corrosion cast, such as nodular protrusions, holes, and enlarged vessels.

CONCLUSIONS

The postcardinal vein first supplies only the mesonephric tissue as a portal vessel. Then it becomes a common source for both kidney generations. Finally it supplies only the metanephric tissue with venous blood. However, two independent vessels were found to supply the cranial renal regions: the anterior mesonephric portal vein and the cranial metanephric portal vein.

Research applications using pigs

The pig is an excellent research model for numerous human conditions and diseases. As a consequence, valuable information has been generated that has direct applications for human medicine. Research with an applied or agriculture-based emphasis also is essential to commercial pork production. Information must be exchanged between researchers using the pig as a biomedical model and investigators conducting applied research. The numerous research applications using the pig illustrate that the pig is a valuable resource for both biomedical and applied research.

Development and degeneration of the arterial system in the mesonephros and metanephros of chicken embryos

BACKGROUND

The general morphology of the mesonephric and metanephric arteries in chicken embryos has already been described previously. Moreover, the general basis of glomerulogenesis has also been established. However, the degeneration of the mesonephric vascular system, and especially glomerular degeneration, have not been well established yet. Also the morphology of the metanephric angiogenic buds has not been studied yet.

METHODS

Scanning electron microscopy of vascular corrosion casts and critical point dried specimens as well as light microscopy of serially sectioned material has been used in this study. Mesonephric degeneration coincides in time with metanephros growth and maturation in the developmental stages of chicken embryos chosen for this investigation (7.5, 9, 11, and 14 days of incubation).

RESULTS

The arterial system of the mesonephros in embryonic chicken is similar to that of the anuran kidney, as described in the literature. The morphology of the degenerating mesonephric glomeruli shows that the glomerular capillaries are more thick, tortuous, and numerous than those in normal glomeruli. The podocytes also show degeneration. The arterial system of the metanephros grows directly from the aorta and from the mesonephric arterial system. During these stages of rapid growth, the metanephros shows angiogenic buds. These angiogenic buds can be either pointed or round blind endings.

CONCLUSIONS

The distribution and topography of the mesonephric and metanephric arteries is in general accordance with the literature. The process of glomerular degeneration in the mesonephros seems similar to glomerular senescence in man but is different from that of the aged rat glomeruli. The round angiogenic buds observed in the metanephros resemble tumoral angiogenic buds in some aspects. However, both angiogenesis and the degenerative phenomena are part of the normal developmental process. Consequently, the involved mechanisms are probably under sole genetic control. The system studied here offers therefore the possibility to study vascular growth and degeneration on the same model in physiological conditions without application of vasoactive or pathological agents.

An immunohistochemical study on the embryonic development of renin-containing cells in the mouse and pig

The prenatal occurrence and distribution of renin-containing (RC) cells were investigated immunohistochemically in mouse and pig embryos. The RC cells of the mouse embryo were first observed at the 13th day of gestation at the walls of the renal, the mesonephric, the adrenal, the abdominal arteries, the adrenal glands and the testis. As the gestation of the mouse progressed, the RC cells had a tendency to localize in areas of the vascular pole of the metanephric glomerulus. In pig, when CRL was 0.8-2.0 cm, RC cells first appeared at the ventral walls of the dorsal aorta, the omphalo-mesenteric (i.e., the cranial mesenteric), the mesonephric, the mesonephric afferent glomerular arteries/arterioles and the inside of the mesonephric glomerulus. As the length of the pig embryo increased, no renin-immunoreactivity could be demonstrated at the degenerated mesonephros, while in the metanephros marked immunoreactivities were found only at the terminal regions of intralobular arteries, i.e., afferent arterioles or the vascular pole of the glomerulus.

Transmission and scanning electron microscopy of the kidney: Part II

The minipig has a multilobar kidney with a wide cortex and short papilla. The vascular bundles are of a simple type. Although short and long looped nephrons are both present, the short looped kind predominates. The minipig has many morphological similarities to dog and human kidneys. One particularly unique feature of the minipig papillary collecting duct cells, however, is the presence of electron-dense granules in the basal cytoplasm which appear to be secreted into the lateral intercellular spaces, perhaps forming a water-tight seal in a manner analogous to membrane-coating granules found in the epidermis of skin.

The shape of renal vasa recta capillaries and its effect on calculation of single capillary blood flow

Previous studies of the renal papilla of the rat have suggested that the vasa recta capillaries can be well approximated by elliptical cylinders (C. Holliger, K. V. Lemley, S. L. Schmitt, F. C. Thomas, C. R. Robertson, and R. L. Jamison, 1983, Circ. Res., 53, 401-413). This hypothesis was validated in a morphological study employing several methods of specimen fixation and preparation. Papillas of young (body wt = 90 g) Wistar rats were fixed and subsequently examined by light and electron microscopy. Cross-sectional shapes and orientations were determined for 300 superficial vasa recta. The ratio, beta, of vessel cross-sectional major-axis-to-minor-axis lengths was 1.39 +/- 0.24 (SD). Values of beta greater than 1.0 (the value expected for circular vessels) could not be accounted for by either fixation artifact or the angle of histologic sectioning of the papillas. A quantitative estimate of the relationship between the apparent capillary diameter measured in vivo and the capillary cross-sectional area was made using a mathematical model which accounts for cross-sectional shapes and orientations of the vasa recta. This estimate implies that current methods of calculating single vas rectum blood flow using apparent diameters and blood velocities determined in vivo probably overestimate actual blood flow by about 25%.

The pig mesonephros. III. Distal tubule, collecting tubule, and Wolffian duct: SEM- and TEM-studies

The ultrastructure of the distal and collecting tubules of mature pig mesonephroi (41st gestational day) was studied in perfusion-fixed embryos. In the distal tubule, the three subsegments postulated on the basis of enzyme histochemistry show only minor differences of their luminal surfaces, mostly of cell size. TEM photographs reveal a single cell type with interdigitating basolateral processes, frequently flattened to 30-120 nm lamellae devoid of organelles. Larger interdigitating processes harbor vertically oriented mitochondria in the form of indented plates. The macula densa cells are small, do not interdigitate, and have distended intercellular spaces. The collecting tubule starts with a dorsal convolution, in which intercalated cells (with apical microfolds and numerous mitochondria) occur in addition to interdigitating cells. Further down this segment, the interdigitating cells are gradually replaced by principal cells characterized by interlocking lateral microvilli, basal infoldings, and relatively few organelles. Intercalated cells extend into the Wolffian duct. Although the pig mesonephros has the most differentiated nephron of the mammals studied so far, with metanephros-like cells, its intrinsic urinary concentrating capacity appears to be low in view of its vascularization pattern and nephron architecture.

Renin immunohistochemistry in the mesonephros and metanephros of the pig embryo

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.