Integration of epithelial patterning and morphogenesis in Drosophila ovarian follicle cells.

Drosophila oogenesis involves the coordinated development of germ cells and an overlying follicular epithelium. The follicle cells provide a genetically tractable system to investigate the cell biology of patterning and morphogenesis. Follicle cells initially form a cuboidal epithelium surrounding a syncytium of nurse cells and oocyte. Epithelial structure is maintained as these cells reorganize to create the three dimensional architecture of the eggshell. Both long-range and short-range cell-cell communications pattern the domains of follicle cells that will create specific eggshell structures. After terminal differentiation to deposit the eggshell proteins, the follicle cells die. This review summarizes recent progress in understanding the cell-cell communication that orchestrates follicle cell patterning and migrations. DE-cadherin-mediated adhesion is important at several steps in egg chamber formation and follicle cell migration. Notch signaling is critical during each successive round of patterning and migration. Integration of bone morphogenetic protein (BMP) and epidermal growth factor (EGF) signals patterns the elaborate structures of the dorsal-anterior eggshell.     

Meal patterning in the streptozotocin-diabetic rat.

The free feeding behavior of 5 streptozotocin-diabetic rats and 5 sham injected rats was monitored both prior to and after the induction of diabetes. After streptozotocin injection, there was a marked increase in total intake resulting from the ingestion of large meals of long durations. Neither the postprandial relationship nor the circadian intake cycle were altered during diabetes. The results were interpreted as supporting the glucostatic theory of food intake regulation and suggest that the principal influence of insulin on feeding behavior is to promote the termination of feeding bouts.     

Oroesophageal factors in the patterning of drinking.

Eleven albino rats were fitted with chronic gastric fistulas to determine the effect of stomach draining on the pattern of drinking. Each animal was given ten two-hr drinking tests with the gastric fistula open on every other test. On the first open fistula test intake was five times greater than that of the following closed fistula test. However, the first fistula opening did not alter the temporal position of the first pause in intake. Across subsequent open, but not closed fistula tests, consumption increased further so that on the last test open fistula intake was ten times greater than in closed fistula intake. On the basis of these results it is suggested that the early portion of the drinking sequence is under the control of conditioned oroesophageal stimuli while the later phases of the sequence are controlled by stimuli arising from the alimentary canal and/or blood.     

Global patterning of the vertebrate mesoderm.

We describe recent advances in the understanding of patterning in the vertebrate post-cranial mesoderm. Specifically, we discuss the integration of local information into global level information that results in the overall coordination along the anterioposterior axis. Experiments related to the integration of the axial and appendicular musculoskeletal systems are considered, and examples of genetic interactions between these systems are outlined. We emphasize the utility of the terms primaxial and abaxial as an aid to understanding development of the vertebrate musculoskeletal system, and hypothesize that the lateral somitic frontier is a catalyst for evolutionary change.     

Rethinking axial patterning in amphibians.

Recent revisions in the Xenopus laevis fate map led to the designation of the rostral/caudal axis and reassignment of the dorsal/ventral axis (Lane and Smith [1999] Development 126:423-434; Lane and Sheets [2000] Dev. Biol. 225:37-58). It is unprecedented to reassign primary embryonic axes after many years of research in a model system. In this review, we use insights about vertebrate development from anatomy and comparative embryology, as well as knowledge about gastrulation in frogs, to reexamine several traditional amphibian fate maps. We show that four extant maps contain information on the missing rostral/caudal axis. These maps support the revised map as well as the designation of the rostral/caudal axis and reassignment of the dorsal/ventral axes. To illustrate why it is important for researchers to use the revised map and nomenclature when thinking about frog and fish embryos, we present an example of alternative interpretations of "dorsalized" zebrafish mutations.     

Enteric nervous system patterning in the avian hindgut.

The enteric nervous system (ENS) is principally derived from vagal and sacral neural crest cells that migrate throughout the gastrointestinal tract before differentiating into neurons and glia. These cells form two concentric rings of ganglia and regulate intestinal motility, absorption, and secretion. Abnormalities of ENS development can lead to disorders of intestinal function, including Hirschsprung's disease. These disorders are generally limited to the distal hindgut, suggesting unique features to development of this region. This study characterized the normal spatiotemporal development of the ENS within the avian hindgut. Neural crest cells begin to populate the hindgut at E8, with patterning of both plexuses complete by embryonic day 9. Crest-derived cells arrive in the submucosal layer before the myenteric layer, as well as differentiate to a neuronal phenotype first. The cloaca demonstrates a unique pattern, characterized by a disorganized myenteric plexus and a flattened nerve of Remak. Detailed understanding of normal avian hindgut ENS development will allow better utilization of this model system to study abnormalities of the intestinal nervous system.     

Hox patterning of the vertebrate axial skeleton.

The axial skeleton in all vertebrates is composed of similar components that extend from anterior to posterior along the body axis: the occipital skull bones and cervical, thoracic, lumbar, sacral, and caudal vertebrae. Despite significant changes in the number and size of these elements during evolution, the basic character of these anatomical elements, as well as the order in which they appear in vertebrate skeletons, have remained remarkably similar. Through extensive expression analyses, classic morphological perturbation experiments in chicken and targeted loss-of-function analyses in mice, Hox genes have proven to be critical regulators in the establishment of axial skeleton morphology. The convergence of these studies to date allows an emerging understanding of Hox gene function in patterning the vertebrate axial skeleton. This review summarizes genetic and embryologic findings regarding the role of Hox genes in establishing axial morphology and how these combined results impact our current understanding of the vertebrate Hox code.     

Abelson tyrosine kinase is required for Drosophila photoreceptor morphogenesis and retinal epithelial patterning

Coordinated differentiation and morphogenesis transform the Drosophila retina from a layer of epithelial cells into a complex three‐dimensional organ. In this study we show that the Abelson (Abl) tyrosine kinase localizes to the dynamically remodeling apical‐junctional membrane domains of the developing photoreceptor cells. Analyses of abl mutant clone phenotypes demonstrate that abl is required for enriched localization of adherens junction and apical polarity complex proteins at photoreceptor–photoreceptor cell junctions and apical membrane domains, respectively, for rhabdomere generation and for spatial organization of ommatidial cells along the apical–basal axis of the epithelium. Loss of abl does not alter expression or localization of Enabled (Ena) nor does heterozygosity for ena dominantly suppress the abl phenotypes, suggesting the downstream effector mechanisms used by Abl in the eye may differ from those used in the embryo. Together our results reveal a prominent role for Abl in coordinating multiple aspects of photoreceptor morphogenesis. Developmental Dynamics 240:1745–1755, 2011. © 2011 Wiley‐Liss, Inc.     

Cardiac patterning and morphogenesis in zebrafish.

Development of the embryonic vertebrate heart requires the precise coordination of pattern formation and cell movement. Taking advantage of the availability of zebrafish mutations that disrupt cardiogenesis, several groups have identified key regulators of specific aspects of cardiac patterning and morphogenesis. Several genes, including gata5, fgf8, bmp2b, one-eyed pinhead, and hand2, have been shown to be relevant to the patterning events that regulate myocardial differentiation. Studies of mutants with morphogenetic defects have indicated at least six genes that are essential for cardiac fusion and heart tube assembly, including casanova, bonnie and clyde, gata5, one-eyed pinhead, hand2, miles apart, and heart and soul. Furthermore, analysis of the jekyll gene has indicated its important role during the morphogenesis of the atrioventricular valve. Altogether, these data provide a substantial foundation for future investigations of cardiac patterning, cardiac morphogenesis, and the relationship between these processes.     

A resegmentation‐shift model for vertebral patterning

Segmentation of the vertebrate body axis is established in the embryo by formation of somites, which give rise to the axial muscles (myotome) and vertebrae (sclerotome). To allow a muscle to attach to two successive vertebrae, the myotome and sclerotome must be repositioned by half a segment with respect to each other. Two main models have been put forward: ‘resegmentation’ proposes that each half‐sclerotome joins with the half‐sclerotome from the next adjacent somite to form a vertebra containing cells from two successive somites on each side of the midline. The second model postulates that a single vertebra is made from a single somite and that the sclerotome shifts with respect to the myotome. There is conflicting evidence for these models, and the possibility that the mechanism may vary along the vertebral column has not been considered. Here we use DiI and DiO to trace somite contributions to the vertebrae in different axial regions in the chick embryo. We demonstrate that vertebral bodies and neural arches form by resegmentation but that sclerotome cells shift in a region‐specific manner according to their dorsoventral position within a segment. We propose a ‘resegmentation‐shift’ model as the mechanism for amniote vertebral patterning.     

The bcl-2 proto-oncogene and the gastrointestinal epithelial tumor progression model.

We report overexpression of the proto-oncogene bcl-2 in gastrointestinal adenocarcinoma and its precursor lesions. The bcl-2 proto-oncogene is centrally involved in the oncogenesis of human follicular lymphoma via a chromosomal translocation t(14;18)(q32;q21) and is also expressed in the epithelial regenerative compartment or the basal crypts of the normal colon and small intestine. We describe an immunohistochemical analysis of fixed, paraffin-embedded tissue using both a polyclonal rabbit and a monoclonal mouse antibody to the Bcl-2 protein. In addition to confirming bcl-2 expression in normal colonic and small intestinal crypts, we also observed expression in the gastric epithelial regenerative compartment, the mucous neck region. No increased expression was found in nonneoplastic or inflammatory gastrointestinal conditions, including ulcerative colitis, Crohn's disease, or inflammatory or hamartomatous polyps. Increased bcl-2 expression, however, was present in hyperplastic colonic polyps and in the majority of dysplastic lesions, from the earliest precursors through large adenomas, high grade flat dysplasia, and adenocarcinoma, all in comparison with adjacent internal control normal epithelium. Increased expression was present in dysplastic glandular lesions from all gastrointestinal sites, including colon, small bowel, and stomach. Furthermore, bcl-2 expression was frequently abnormal in nondysplastic epithelium surrounding dysplastic lesions, suggesting that altered expression occurred before the development of morphological dysplasia. Specifically, directly contiguous morphologically nondysplastic epithelium often showed abnormal bcl-2 expression throughout the full length of the crypt-villus axis. This expression pattern gradually diminished to involve only the crypt base (the normal pattern of expression), proceeding away from malignant or dysplastic lesions. Abnormal bcl-2 immunoreactivity in 1), the earliest precursor dysplastic lesions and its persistence throughout neoplastic progression and 2), contiguous morphologically unaltered nondysplastic epithelium suggests that bcl-2 alterations occur early during the morphological and molecular sequence of events leading to gastrointestinal epithelial neoplasia.     

Colonic epithelial cell proliferation in a rat model of nongenotoxin-induced colonic neoplasia.

BACKGROUND: The effect on colonic cell proliferation of poligeenan, a nongenotoxic polysaccharide that induces colon tumors in rats, was compared with guar gum and carrageenan. EXPERIMENTAL DESIGN: Fischer 344 rats were fed a basal diet supplemented with carrageenan and poligeenan fibers for up to 91 days. The quantitative levels of proliferation, location of the proliferating cells, and the ability of the mucosa to readapt by removing the experimental fibers from the diet were tested. RESULTS: The mucosal epithelium exhibited a 5-fold increase in thymidine kinase activity in both the carrageenan and poligeenan groups. Proliferating cells appeared at the luminal surface only in the poligeenan-treated rats, and the number of proliferating cells in the upper third of the crypt increased 35-fold. A second and third set of animals were fed one of the three test diets for either 28 or 64 days, followed by a 28-day recovery period. Proliferation in the guar- and carrageenan-treated groups returned to basal levels. In poligeenan-treated rats, thymidine kinase levels, and proliferating cells in the upper third of the crypt remained 2- and 11-fold, respectively, above controls. CONCLUSIONS: The difference in recovery time between the poligeenan group and the others, and the luminal location of proliferating cells may prove useful as markers in understanding early events in the carcinogenic process induced by a nongenotoxin.     

Zebrafish neural induction and patterning.

Formation of a functional nervous system requires that distinct types of cells develop at quite precise times and places. A goal of developmental neurobiologists is to understand the nature of the patterning mechanisms that specify neural cells for particular fates. In recent years, zebrafish has emerged as new model system for investigating vertebrate neural development, offering a unique combination of genetic, cellular, and molecular tools. Studies using zebrafish provide important new insights concerning the source and nature of molecular signals that induce and pattern the central nervous system.     

Loss of the Tg737 protein results in skeletal patterning defects.

Tg737 mutant mice exhibit pathologic conditions in numerous tissues along with skeletal patterning defects. Herein, we characterize the skeletal pathologic conditions and confirm a role for Tg737 in skeletal patterning through transgenic rescue. Analyses were conducted in both the hypomorphic Tg737(orpk) allele that results in duplication of digit one and in the null Tg737(delta2-3betaGal) allele that is an embryonic lethal mutation exhibiting eight digits per limb. In early limb buds, Tg737 expression is detected throughout the mesenchyme becoming concentrated in precartilage condensations at later stages. In situ analyses indicate that the Tg737(orpk) mutant limb defects are not associated with changes in expression of Shh, Ihh, HoxD11-13, Patched, BMPs, or Glis. Likewise, in Tg737(delta2-3betaGal) mutant embryos, there was no change in Shh expression. However, in both alleles, Fgf4 was ectopically expressed on the anterior apical ectodermal ridge. Collectively, the data argue for a dosage effect of Tg737 on the limb phenotypes and that the polydactyly is independent of Shh misexpression.     

Role of glomerular epithelial cell injury in the pathogenesis of glomerular scarring in the rat remnant kidney model.

We investigated the roles of glomerular epithelial cell (GEC) pathology and dysfunction in the pathogenesis of glomerular scarring and attempted to separate them from direct hypertensive injury in the 5/6 nephrectomy (RK) model of glomerular injury. Male WKY rats weighing 200 g were studied 6 weeks after RK, when approximately one-half had developed systemic hypertension (systolic blood pressure > or = 150 mm Hg) (HT), and one-half were normotensive (NT). The incidence of glomerular necrosis and scarring was greatest in the HT rats (P = 0.0259), and vascular necrosis was only seen in 4 of 11 HT rats. The RK group had increased glomerular diameters (HT, 174 mu mean; NT, 171 mu; sham, 142 mu; P = 0.0014 by analysis of variance). There was foot process effacement in the HT and NT groups (HT, 104 filtration slits/100 mu glomerular basement membrane; NT, 112 mu; sham, 143 mu; P < 0.005 by analysis of variance), but GEC separation from the glomerular basement membrane was not significant in either HT or NT rats. GEC function was determined from protamine-heparin aggregate disappearance curves, and the curves, representing GEC endocytosis, were not different in either HT or NT groups compared with the sham-operated groups. These findings suggest that GEC function is preserved in RK, and the changes in glomerular size and GEC morphology are nonlethal and adaptive. The morphological appearance of the acute glomerular and vascular lesions and their presence only in HT animals is consistent with a hypertensive pathogenesis. The glomerular sclerosis seen in both HT and NT may result from either resolution of acute lesions with scarring and/or adaptive changes in glomerular structure and cellular functions other than the GEC clearance function we studied.     

Meal patterning in the lactating rat

The present study was undertaken to investigate feeding behaviour of the lactating rat over the day-night cycle. Food intake was recorded continuously in six pregnant and subsequently lactating female rats with 10 pups each. Although there was a twofold increase of food intake during the first post partum week, the meal frequency did not increase above the level of previous weeks. Only the mean meal size increased. After this week food intake increased to three times the normal intake, meal size did not change but meal frequency increased in favour of daytime meals. It is suggested that with moderate caloric demands food intake regulation in the rat occurs through changes in meal size. With higher energy requirements, however, meal frequency is also affected. The possible causal factors involved in the change in feeding are discussed.     

Developmental patterning of the myocardium

The heart in higher vertebrates develops from a simple tube into a complex organ with four chambers specialized for efficient pumping at pressure. During this period, there is a concomitant change in the level of myocardial organization. One important event is the emergence of trabeculations in the luminal layers of the ventricles, a feature which enables the myocardium to increase its mass in the absence of any discrete coronary circulation. In subsequent development, this trabecular layer becomes solidified in its deeper part, thus increasing the compact component of the ventricular myocardium. The remaining layer adjacent to the ventricular lumen retains its trabeculations, with patterns which are both ventricle- and species-specific. During ontogenesis, the compact layer is initially only a few cells thick, but gradually develops a multilayered spiral architecture. A similar process can be charted in the atrial myocardium, where the luminal trabeculations become the pectinate muscles. Their extent then provides the best guide for distinguishing intrinsically the morphologically right from the left atrium. We review the variations of these processes during the development of the human heart and hearts from commonly used laboratory species (chick, mouse, and rat). Comparison with hearts from lower vertebrates is also provided. Despite some variations, such as the final pattern of papillary or pectinate muscles, the hearts observe the same biomechanical rules, and thus share many common points. The functional importance of myocardial organization is demonstrated by lethality of mouse mutants with perturbed myocardial architecture. We conclude that experimental studies uncovering the rules of myocardial assembly are relevant for the full understanding of development of the human heart.     

An in vitro model for immune control of chlamydial growth in polarized epithelial cells.

A polarized epithelial culture system and chlamydia-specific T-cell lines and clones were employed to investigate the ability and mechanisms by which T cells control the growth of chlamydiae in epithelial cells. Monolayers of polarized mouse epithelial cells were infected with the Chlamydia trachomatis agent of mouse pneumonitis (MoPn) and then exposed to antigen-stimulated MoPn-specific T-cell lines and clones. The results revealed that in vivo-protective MoPn-specific T-cell lines and clone 2.14-0 were capable of inhibiting the growth of MoPn in polarized epithelial cells. In contrast, the nonprotective MoPn-specific T-cell clone 2.14-3, naive splenic T cells, and a control T-cell clone could not inhibit the growth of MoPn in epithelial cells. Transmission electron microscopic analysis of infected epithelial cells which were exposed to clone 2.14-0 confirmed the absence of an established infection, as deduced from the virtual absence of inclusions in the cells. Antigen-specific activation of clone 2.14-0 was required for the MoPn-inhibitory function, since the absence of antigenic stimulation or stimulation with a heterologous chlamydial agent did not result in MoPn growth inhibition. Activation of clone 2.14-0 resulted in acquisition of the capacity to inhibit growth of both homologous (MoPn) and heterologous chlamydial agents. Close interaction between epithelial cells and clone 2.14-0 was required for the MoPn-inhibitory action, because separation of the cell types by a filter with a pore size of 0.45, 3.0, or even 8.0 microns abrogated MoPn inhibition. Protective T cells may act at close range in the epithelium to control chlamydial growth, possibly involving short-range-acting cytokines. The ability of antigen-stimulated T-cell lines and clones to inhibit chlamydial growth in polarized epithelial cultures could be a useful method for identifying protective T-cell clones and antigenic peptide fragments containing protective epitopes.