The occluding junctions of mouse duodenal enterocytes during development

Summary The architecture of occluding junctions during the differentiation of the mouse duodenum was studied in freeze-fractured material. Irregular zonulae occludentes (ZO) (Type I) are numerous during fetal life, and are characterized by their irregular width, and by the presence of basal open-ended extensions fused with the discontinuous basal strand of the ZO. Regular ZOs (Type II), typical of the adult villous epithelium, appear after Type I junctions by day 16 of gestation. Two patterns are distinguishable: in the first, parallel strands of ridges and furrows are found without crossing branches; in the second pattern, the junction zone is organized like a network of short branches forming various types of polygons. In fetal and adult mice fasciae occludentes (FO) (Type III) are present on the lateral cell membranes; in unfixed specimens particles are found in the furrows of the E-face and pits on the ridges of the P-face. In fixed tissues, the particles are aligned on the ridges of the P-face. These results indicate that fixation with glutaraldehyde modifies considerably the affinity of junctional particles toward the P-face during the fracture process. Moreover, the presence of numerous large FOs on the lateral cell membranes of enterocytes during late fetal life and in the adult, is possibly related to cell movement along the intestinal villi.     

Coat proteins isolated from clathrin coated vesicles can assemble into coated pits

Isolated human fibroblast plasma membranes that were attached by their extracellular surface to a solid substratum contained numerous clathrin coated pits that could be removed with a high pH buffer (Moore, M.S., D.T. Mahaffey, F.M. Brodsky, and R.G.W. Anderson. 1987. Science [Wash. DC]. 236:558-563). When these membranes were incubated with coat proteins extracted from purified bovine coated vesicles, new coated pits formed that were indistinguishable from native coated pits. Assembly was dependent on the concentration of coat protein with half maximal assembly occurring at 7 micrograms/ml. Assembly was only slightly affected by the presence of divalent cations. Whereas normal appearing lattices formed in a low ionic strength buffer, when assembly was carried out in a low pH buffer, few coated pits were evident but numerous small clathrin cages decorated the membrane. Coated pits did not form randomly on the surface; instead, they assembled at differentiated regions of membrane that could be distinguished in carbon/platinum replicas of frozen and etched membranes by the presence of numerous particles clustered into patches the size and shape of a coated pit.     

Substrate selection for pit making and oviposition in an antlion, Myrmeleon bore Tjeder, in terms of sand particle size

The larvae of the pit‐making antlion Myrmeleon bore Tjeder live in open sand in riverbeds with a substratum consisting of various particle sizes. We analyzed the spatial distribution of their pits in a sandy floodplain to determine their larval and adult responses to the heterogeneous substrate. The spatial distribution pattern of their pits had an aggregated distribution, and there was a significant positive correlation between pit density and the ratio of medium‐size sand particles to total weight of sand. We examined the size of sand particles selected in the larval pit‐building behavior and the oviposition behavior of the adult. Both larvae and adults selected medium‐size sand particles. The larvae of M. bore are relatively sedentary predators and rarely move great distances. Thus, the present results suggest that habitat selection by adult females is a major factor causing the aggregative distribution of the pits.     

Proliferation of cardiomyocytes and interstitial cells in the cardiac muscle of the mouse during pre- and postnatal development

Proliferation of cardiomyocytes and interstitial cells in the cardiac ventricle of the mouse during pre- and postnatal development was studied. Furthermore, the number of cardiomyocyte and interstitial cell nuclei per unit area was determined on histological sections. The labelling index of cardiomyocytes decreases from 23% on day 14 of gestation to about zero at 3 weeks after birth. The number of cardiomyocyte nuclei per unit area increases up to day 16 of gestation and then continuously declines. This coincides with the concept that the increase in size of the heart during early fetal life is mainly due to hyperplasia, while during late fetal life and after birth it is mainly, and during adult life exclusively, due to hypertrophy of cardiomyocytes. Proliferation of interstitial cells continues up to 5 days after birth and then decreases. The ratio of cardiomyocytes to interstitial cells decreases by a factor of about 10 between day 14 of gestation and 3 weeks after birth.     

Proliferation of Cardiomyocytes and Interstitial Cells In the Cardiac Muscle of the Mouse During Pre- and Postnatal Development

Proliferation of cardiomyocytes and interstitial cells in the cardiac ventricle of the mouse during pre- and postnatal development was studied. Furthermore, the number of cardiomyocyte and interstitial cell nuclei per unit area was determined on histological sections. The labelling index of cardiomyocytes decreases from 23% on day 14 of gestation to about zero at 3 weeks after birth. the number of cardiomyocyte nuclei per unit area increases up to day 16 of gestation and then continuously declines. This coincides with the concept that the increase in size of the heart during early fetal life is mainly due to hyperplasia, while during late fetal life and after birth it is mainly, and during adult life exclusively, due to hypertrophy of cardiomyocytes. Proliferation of interstitial cells continues up to 5 days after birth and then decreases. the ratio of cardiomyocytes to interstitial cells decreases by a factor of about 10 between day 14 of gestation and 3 weeks after birth.     

Comparative anatomy of intervessel pits in two mangrove species growing along a natural salinity gradient in Gazi bay, Kenya

BACKGROUND AND AIMS: According to the air-seeding hypothesis, embolism vulnerability in xylem elements is linked directly to bordered pit structure and functioning. To elucidate the adaptive potential of intervessel pits towards fluctuating environmental conditions, two mangrove species with a distinct ecological distribution growing along a natural salinity gradient were investigated. METHODS: Scanning and transmission electron microscopic observations were conducted to obtain qualitative and quantitative characteristics of alternate intervessel pits in A. marina and scalariform intervessel pits in Rhizophora mucronata. Wood samples from three to six trees were collected at seven and five sites for A. marina and R. mucronata, respectively, with considerable differences between sites in soil water salinity. KEY RESULTS: Vestured pits without visible pores in the pit membrane were observed in A. marina, the mangrove species with the widest geographical distribution on global as well as local scale. Their thick pit membranes (on average 370 nm) and minute pit apertures may contribute to reduced vulnerability to cavitation of this highly salt-tolerant species. The smaller ecological distribution of R. mucronata was in accordance with wide pit apertures and a slightly higher pitfield fraction (67 % vs. 60 % in A. marina). Nonetheless, its outer pit apertures were observed to be funnel-shaped shielding non-porous pit membranes. No trends in intervessel pit size were observed with increasing soil water salinity of the site. CONCLUSIONS: The contrasting ecological distribution of two mangrove species was reflected in the geometry and pit membrane characteristics of their intervessel pits. Within species, intervessel pit size seemed to be independent of spatial variations in environmental conditions and was only weakly correlated with vessel diameter. Further research on pit formation and function has to clarify the large variations in intervessel pit size within trees and even within single vessels.     

A system of intraependymal cisternae along the margins of the median eminence in the rat: Structure,three-dimensional arrangement and ontogeny

Summary Structure, three-dimensional arrangement and ontogeny of large intracellular cisternae located in the median eminence region of the rat hypothalamus were studied using toluidin-blue stained semithin sections and electron microscopy. The cisternae occur along the projections of ependymal cells lining the ventral portion of the third ventricle (infundibular recess). Small cisternae can be seen close to the ventricle, whereas larger ones, divided into smaller compartments by thin septa, cluster near the surface of the hypothalamus. The cisternae are encompassed by a thin layer of cytoplasm to which axon terminals containing synaptic and dense core vesicles are closely related. Cisternae are arranged around the median eminence in a characteristic pattern. They occupy the midline in the retrochiasmatic area, flank both margins of the median eminence and extend caudally behind the origin of the pituitary stalk. The cisternae appear first between the 15th and 17th postnatal days. At about the 30th day their size and distribution resemble the situation observed in adult animals. The ependymal cisternae are suggested to be closely related to the luteinizing-hormone releasing-hormone (LH-RH)-containing fibers.     

Prostaglandin E2 and leukotriene C4-induced luteinizing hormone-releasing hormone release from immature and adult male rat median eminences in vitro: eicosanoid formation and binding parameters

The amounts of prostaglandin E2 formed in vitro by the median eminences of adult male rats were greater than those produced by the median eminences of immature, 22 day-old rats. However, the amount of leukotriene C4 produced by the adult rat median eminences was lower than that produced by the immature rat median eminences. Analysis of the prostaglandin E2 binding parameters of hypothalamic P2 membrane fractions indicates that there are two binding components, one high affinity (RH) and one low affinity (RL) in both adult and immature rats. The maximal binding capacity of RH from adult rat membranes was significantly lower than that of immature rat membranes, correlating with greater prostaglandin E2 production by the adult rat median eminence. Only one leukotriene C4 binding site was detected in both adult and immature rat membranes. Exogenous prostaglandin E2 and leukotriene C4 both stimulated, the release of luteinizing hormone-releasing hormone to the same extent from both the adult and immature median eminences.     

Vitamin D-dependent calcium-binding protein. Changes during gestation, prenatal and postnatal development in rats

During the perinatal period, calcium metabolism is stressed. As intestinal Ca-binding protein is considered as a molecular expression of the hormonal effect of 1,25-dihydroxycholecalciferol (1,25(OH)2D3), Ca-binding protin measurements may document the vitamin D roles during this period. We describe the variations of Ca-binding protein concentrations in the rat during the last 5 days of gestation, in the maternal duodenum, placentas, fetal membranes and fetal intestines. We also report intestinal Ca-binding protein changes from birth until weaning. The evolution of the maternal intestinal Ca-binding protein, which increases on day 19.5 of gestation, is consistent with that of calcium intestinal absorption and may be explained by increased 1,25(OH)2D3 production. Placental Ca-binding protein rises from day 17.5 until the end of gestation, and may be related to the profile of calcium transfer from mother to fetuses. It is noteworthy that the placental Ca-binding protein is predominantly found in the fetal part of the organ where materno-fetal exchanges occur. The yolk sac synthesizes substantial amounts of Ca-binding protein. In the fetal membranes, Ca-binding protein plateaus from day 17.5 until day 20.5 and decreases on day 21.5. The Ca-binding protein presence in the fetal placenta and in the yolk sac may suggest that these tissues are also targets for vitamin D. In the fetus the intestinal Ca-binding protein s is detected as early as day 17.5 of gestation and increases markedly during the last day of gestation. From birth and during the first 3 weeks of postnatal life, the intestinal Ca-binding protein concentration does not change. It undergoes a sharp rise just at the time of weaning. We have also shown that the specific distribution of Ca-binding protein along the intestine is acquired during intrauterine life and does not change with sucking or weaning. The two main changes of intestinal Ca-binding protein, observed just before birth and at weaning, may reflect the intestinal maturation and/or variations in vitamin D metabolism.     

The fate of fetal Leydig cells during the development of the fetal and postnatal rat testis

The ultrastructure and developmental fate of the fetal generation of Leydig cells of the rat testis was studied from the 17th day of fetal life up to 100 days after birth. The number of fetal Leydig cells per testis was determined by light microscopic morphometric analysis of semithin plastic sections. In fetal testes (days 17-22 postconception), Leydig cells exhibited a characteristic ultrastructure, containing smooth endoplasmic reticulum, many lipid inclusions and glycogen. Testes of 17-day-old fetuses contained about 25 x 10(3) fetal Leydig cells, rapidly increasing to 90 x 10(3) per testis in 21-day-old fetuses. After birth, fetal Leydig cells per testis remained relatively constant up to 2 weeks (80-90 x 10(3) per testis) and were identified by light and electron microscopy which showed their numerous lipid inclusions, their tendency for clustering and their association with interstitial tissue fibroblasts which partly encapsulated the fetal Leydig cells. From 21-100 days after birth, fetal Leydig cell numbers were quite variable with a mean of 45-60 x 10(3) per testis. These results are the first to show that the fetal generation of Leydig cells persist in the adult testis and do not undergo early postnatal degeneration or dedifferentiation into other interstitial cells. The simultaneous occurrence of the fetal Leydig cells and the adult population of Leydig cells indicates that these cells are distinct cell generations which are developmentally unrelated.     

Vertical and radial profiles in tracheid characteristics along the trunk of Douglas-fir trees with implications for water transport

The main stems of three young Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirbel) Franco) trees were dissected to obtain samples of secondary xylem from internodes axially along the trunk and radially within each internode. From these samples, measurements were obtained of tracheid diameter, length, the number of inter-tracheid pits per tracheid, and the diameter of the pit membranes. In addition, samples were obtained along the trunks of three old growth trees and also a small sample of roots for measurement of tracheid diameter. A gradient was apparent in all measured anatomical characters vertically along a sequence among the outer growth rings. These gradients arose not because of a gradient vertically along the internodes, but because of the strong gradients present at each internode among growth rings out from the pith. Tracheid characteristics were correlated: wider and longer tracheids had more numerous pits and wider pits, such that total pit area was about 6% of tracheid wall area independent of tracheid size. A stem model combining growth rings in parallel and internodes in series allowed for estimates of whole trunk conductance as a function of tree age. Conductance of the stem (xylem area specific conductivity) declined during the early growth of the trees, but appeared to approach a stable value as the trees aged.     

Structure and function of bordered pits: new discoveries and impacts on whole-plant hydraulic function

Bordered pits are cavities in the lignified cell walls of xylem conduits (vessels and tracheids) that are essential components in the water-transport system of higher plants. The pit membrane, which lies in the center of each pit, allows water to pass between xylem conduits but limits the spread of embolism and vascular pathogens in the xylem. Averaged across a wide range of species, pits account for > 50% of total xylem hydraulic resistance, indicating that they are an important factor in the overall hydraulic efficiency of plants. The structure of pits varies dramatically across species, with large differences evident in the porosity and thickness of pit membranes. Because greater porosity reduces hydraulic resistance but increases vulnerability to embolism, differences in pit structure are expected to correlate with trade-offs between efficiency and safety of water transport. However, trade-offs in hydraulic function are influenced both by pit-level differences in structure (e.g. average porosity of pit membranes) and by tissue-level changes in conduit allometry (average length, diameter) and the total surface area of pit membranes that connects vessels. In this review we address the impact of variation in pit structure on water transport in plants from the level of individual pits to the whole plant.     

Formation of the pits with taste buds at the lingual root in the striped dolphin,Stenella coeruleoalba

The tongue of the striped dolphin, Stenella coeruleoalba, shows a V-shaped row of pits on its posterior dorsum. Their development is described on the basis of macroscopic and light microscopic observations on fetal, young, and adult stages. Four to eight pits occur, most often five in the adult. Anlagen of the pits first protrude as round epithelial thickenings which later increase in diameter and become thin. The circular primordia then sink, and grooves oriented both circularly and radially develop in the walls of the shallow pits thus formed. Pits and grooves deepen with development so that older pits become lined with conical projections. As pits grow further, they become elongated anterolaterally, retaining slit-like openings. Each pit in the adult is 2–8 mm long and about 1 mm wide. The pits are not derived from lingual gland ducts but develop independently. Taste buds resembling those of other mammalian tongues can be found in young dolphins but are few in number and limited to the thin epithelium of the pit projections and to that of the side wall of the pits. They first appear in the late prenatal period but degenerate in the adult. A rich nerve supply is observable in the lamina propria below taste buds in the calf. The pits and their projections in the dolphin correspond to the vallate papillae of other mammals, but whether each projection or a whole pit corresponds to a single vallate papilla is undecided.     

Maturation of the hypothalamo-neurohypophysial system

Summary Sections of the hypothalamus, median eminence and pituitary from fetal and neonatal rats were examined with the immunoperoxidase staining technique and light microscopy. Purified antisera raised against vasopressin and oxytocin, and antisera cross-reactive with rat neurophysin were used to localize these antigens in the hypothalamo-neurohypophysial system (HNS). Neurophysin was detected throughout the HNS of the 18-day fetal rat. Vasopressin was present in the hypothalamus and pituitary of the 19-day fetus, and in the median eminence of the 4-day neonate. Oxytocin was not detected in the pituitary until 1–2 days after birth, in the hypothalamus after 4 days, and in the median eminence after 8 days. During the first days after birth the supraoptic nucleus was more mature than the paraventricular nucleus. The HNS did not approach maturity until at least 7 days after birth. The relative maturity of the supraoptic nucleus compared with the paraventricular nucleus, and the detection of vasopressin before oxytocin are evidence for the one-neuron-one-hormone theory. The data do not exclude the possibility that the fetal hypothalamo-neurohypophysial system, and perhaps the fetal hormone, vasotocin, affect the initiation and course of parturition.This work was financed by the Medical Research Council of New Zealand     

Cellular differentiation in the kidneys of newborn mice studies with the electron microscope

The structure of the kidney of the Swiss albino mouse changes progressively during the first 2 weeks after birth. Cells proliferate to form new nephrons, cells differentiate by acquiring specialized membranous components, and certain cytological features which are present at birth diminish in abundance or disappear. The differentiation of the cells of the cortical tubules has been studied using the light and electron microscopes. The tubules are partially and variably differentiated at birth. During the first 2 weeks after birth the brush border develops in the proximal tubules by the accumulation of numerous microvilli on the apical cell margins. Basal striations develop in proximal and distal tubules as an alignment of mitochondria, the result of what appears to be progressive interlocking of adjacent fluted cells. The mitochondria increase in number and size, accumulate homogeneous matrix, and acquire small, very dense granules. The collecting ducts develop tight pleating of the basal cell membranes, and dark cells containing numerous small cytoplasmic vesicles and microvilli appear. At birth there are dense irregular cytoplasmic inclusions presumed to be lipide in renal cells, the cytoplasmic granules of Palade are abundant, and there are large round bodies in the cells of the proximal tubules. The lipide inclusions disappear a few days after birth, and the cytoplasmic granules of Palade diminish in abundance as the cells differentiate. The large round bodies in the proximal tubules consist of an amorphous material and contain concentrically lamellar structures and mitochondria. They resemble the cytoplasmic droplets produced in the proximal tubules of adult rats and mice by the administration of proteins. The large round bodies disappear from the proximal tubules of infant mice during the first week after birth, but the concentric lamellar structures may be found in adult mice.     

CELLULAR DIFFERENTIATION IN THE KIDNEYS OF NEWBORN MICE STUDIED WITH THE ELECTRON MICROSCOPE

The structure of the kidney of the Swiss albino mouse changes progressively during the first 2 weeks after birth. Cells proliferate to form new nephrons, cells differentiate by acquiring specialized membranous components, and certain cytological features which are present at birth diminish in abundance or disappear. The differentiation of the cells of the cortical tubules has been studied using the light and electron microscopes. The tubules are partially and variably differentiated at birth. During the first 2 weeks after birth the brush border develops in the proximal tubules by the accumulation of numerous microvilli on the apical cell margins. Basal striations develop in proximal and distal tubules as an alignment of mitochondria, the result of what appears to be progressive interlocking of adjacent fluted cells. The mitochondria increase in number and size, accumulate homogeneous matrix, and acquire small, very dense granules. The collecting ducts develop tight pleating of the basal cell membranes, and dark cells containing numerous small cytoplasmic vesicles and microvilli appear. At birth there are dense irregular cytoplasmic inclusions presumed to be lipide in renal cells, the cytoplasmic granules of Palade are abundant, and there are large round bodies in the cells of the proximal tubules. The lipide inclusions disappear a few days after birth, and the cytoplasmic granules of Palade diminish in abundance as the cells differentiate. The large round bodies in the proximal tubules consist of an amorphous material and contain concentrically lamellar structures and mitochondria. They resemble the cytoplasmic droplets produced in the proximal tubules of adult rats and mice by the administration of proteins. The large round bodies disappear from the proximal tubules of infant mice during the first week after birth, but the concentric lamellar structures may be found in adult mice.     

Expression of extracellular matrix components fibronectin and laminin in the human fetal heart.

It has been well documented that the extracellular matrix components fibronectin and laminin promote or regulate morphogenesis of the myocardial cells in mammalian heart. However, their chronological change of expression (or localization) in the human heart remains elusive. In this study, fibronectin and laminin in the left ventricle of forty-two human fetuses aged from 8 to 26 weeks gestation and left ventricular tissues obtained from a 2-week old infant and two adults were investigated by Western blot analyses and indirect immunofluorescence technique with monoclonal antibodies. In the fetal heart, fibronectins were present along the endocardium, epicardium, and linings of larger blood vessels. In 14-16 weeks gestation, fibronectin immunofluorescence became stronger but not evenly dispersed in the interstitium. After 24 weeks gestation, they were strongly positive only in the relatively larger blood vessels, as well as those in the infant and adult cardiac tissues. Laminins were strongly positive along the endocardium and basement membrane of the myocardial cells and fibroblasts during fetal life. After birth, laminins formed fine fibrillar network along the basement membrane in association with the transverse tubules of myocardial cell; these morphological characteristics remained in the adult cardiac tissues. These results indicate that fibronectin expression is relatively constant during fetal life but decreases after birth; in contrast, laminin expression is not age-dependent and constant throughout the life.     

Carbonic anhydrase activity in the blood of adult sheep, fetal sheep and lambs

The activity of carbonic anhydrase (E.C.4.2.1.1) (CA) has been measured in the blood of adult and fetal sheep and lambs. The mean activity in adult sheep was 0.89 enzyme units (EU) per 100 micrograms of Hb. The activity in fetal sheep aged 90 days was just below 20% of this and in fetuses near full term was just under 40% of the mean adult level. The regression line gave an increase of CA activity (per 100 micrograms Hb) of 0.004 EU/day. The appearance of CA in fetal blood normally occurred before any detectable production of adult Hb. One aberrant fetus showed early development of the adult pattern in the red cells, having adult type Hb and adult levels of CA during the period of 116-128 days of fetal age. In the period after birth the CA level in the blood rose rapidly, reaching the adult level 30 days after birth. During this period activity per 100 micrograms HB increased by 0.014 EU/day, significantly faster than during fetal life.     

A freeze-etch study of the ultrastructure of red algal pit plugs

Summary Freeze-etch studies indicate that the fully-formed pit plug ofPalmaria palmata consists of a homogeneous plug core, a pair of plug caps, and associated membranes. A single cap membrane separates the two layers of each plug cap and is the only membrane found between the cytoplasm and the plug core. Due to the apparent junction of the plasmalemma and cap membranes, the plug core, along with the adjacent plug cap layer on either face of the core, is entirely membrane-bounded and essentially extracellular. Fracture faces of the cap membrane bear large populations of particles which are inconspicuous due to their low profile. The plasmalemma lining the plug core from cell to cell has numerous, very obvious particles on its fracture faces, more even than does the cytoplasmic plasmalemma.The relationship of the rhodophycean pit plug to the fungal septal pore plug is discussed.This report represents a portion of a thesis submitted in partial fulfillment of the requirements of a Master of Science degree, Cornell University, Ithaca, N.Y.     

The ultrastructure of the developing neural lobe

Summary The ultrastructure of the developing neural lobe of rats was studied. The results revealed three periods in its development. The first period lasts till the 17th day of fetal life. At its beginning the anlage of the neural lobe is formed as a mass of cells very similar in appearance and in connection with the subependymal cells of the future median eminence. During the first period the cells of the anlage differentiate into pituicytes, and the penetration of the first nerve fibres and blood vessels among them is seen. The second period is from the 18th day of fetal life till one month after birth. At its beginning the first signs of neurosecretory activity were detected. During the period increasing numbers of neurosecretory fibres penetrate into the neural lobe, and the pituicytes show morphological signs characteristic of active cells. An increase in the functional activity of the neural lobe is also detected. The third period is from the end of the 1st till the end of the third month. During this period the development of the neural lobe proceeds and at the end it has the appearance of the adult gland. During this period the pituicytes gradually lose the signs of activity and at the end of the period they look like those observed in adult animals. Considering the results from the study, together with some data from previous investigations it is suggested that the pituicytes exert some stimulating and regulative influences on the process of neurosecretion in the neural lobe.Research fellow of the Alexander von Humboldt Foundation.