Changes in DNA synthesis and morphometric indexes of the myocardium in albino rats treated with angiotensin II

Autoradiography with ³H-thymidine showed that angiotensin II injected intraperitoneally to newborn albino rats from the 2nd to 6th day of life stimulates DNA synthesis in the myocardium of the left ventricle and increased the area of cardiomyocytes and number and area of nucleoli. Two weeks after treatment the area of cardiomyocytes and the number of nucleoli increased, while the count of PCNA-positive nuclei remained unchanged. Immunohistochemical assay for vimentin showed that the ratio between the number of cardiomyocytes and connective tissue cells remained unchanged. In 45-day-old rats (38 days after treatment) the intensity of DNA synthesis and morphometric indexes of the myocardium did not differ from the control. Fivefold treatment of adult rats with angiotensin II increased the number and area of nucleoli, but had no effect on the count of connective tissue cells.     

Immunofluorescent localization of tenascin during the morphogenesis of the outflow tract of the chick embryo heart

Summary The cono-truncus constitutes a complex segment of the developing heart that gives rise to the outflow tract of the ventricles and root of the pulmonary and aortic arteries. Numerous studies have revealed that the extracellular matrix plays a relevant role in most morphogenetic processes modulating cell behaviour. By means of immunofluorescence, we studied the distribution and possible involvement of tenascin during morphogenesis of the conus and truncus in chick embryo hearts between days 4.5–10 of incubation. Tenascin is an extracellular matrix glycoprotein with a significant role in morphogenesis and cell and tissue differentiation. Our results reveal a specific distribution of tenascin in the areas of the cono-truncus undergoing significant structural changes during morphogenesis of this cardiac segment, appearing mainly in the mesenchymal layer subjacent to the myocardial layer, the cono-truncal ridges and the aorto-pulmonary septum. The distribution of tenascin was compared and contrasted with that of collagen type I, which constitutes a further component of the extracellular matrix common to most developing connective tissues.     

Lineage specification in neural crest cell pathfinding.

There are two principal models to explain neural crest patterning. One assumes that neural crest cells are multipotent precursors that migrate throughout the embryo and differentiate according to cues present in the local environment. A second proposes that the neural crest is a population of cells that becomes restricted to particular fates early in its existence and migrates along particular pathways dependent on unique cell-autonomous properties. Although it is now evident that the neural crest cell population, as a whole, is actually heterogenous (composed of both multipotent and restricted progenitors), evidence supporting the model of prespecification has increased over the past few years. This review will begin by telling the story of melanoblasts: a neural crest subpopulation that is biased toward a single fate and subsequently acquires intrinsic properties that guide cells of this lineage to their final destination. The remainder of this review will explore whether this model is exclusive to melanoblasts or if it can also be used to explain the patterning of other neural crest cells like those of the sensory, sympathoadrenal, and enteric lineages.     

Diverse roles of E-cadherin in the morphogenesis of the submandibular gland: insights into the formation of acinar and ductal structures

The formation of acinar and ductal structures during epithelial tissue branching morphogenesis is not well understood. We report that in the mouse submandibular gland (SMG), acinar and ductal cell fates are determined early in embryonic morphogenesis with E-cadherin playing pivotal roles in development. We identified two morphologically distinct cell populations at the single bud stage, destined for different functions. The outer layer of columnar cells with organized E-cadherin junctions expressed the neonatal acinar marker B1 by E13.5, demonstrating their acinar fate. The interior cells initially lacked distinct E-cadherin junctions, but with morphogenesis formed cytokeratin 7 (K7) -positive ductal structures with organized E-cadherin junctions and F-actin filaments. Inhibition of E-cadherin function with either siRNA or function blocking antibody caused extensive apoptosis of ductal cells and aberrantly dilated lumens, providing the first evidence that E-cadherin regulates ductal lumen formation during branching morphogenesis of the salivary gland.     

Formation of the chick mesonephros

Summary Using colour microinjections the course of mesonephric nephrons was visualized in embryos of White Leghorn chicks on days 5–18. From the stage of the S-shaped body until their full maturity, the nephrons generally retain the S-shaped form, with two main flexures. The first flexure is formed at the point where the tubule runs closest to the Wolffian duct, the second, more distal flexure, at the site of juxtaposition to Bowman's capsule.The cranial, narrow part of the mesonephros contains rudimentary nephrons with mostly obliterated tubules and short nephrons often exhibiting an irregular course. Nephrons of the caudal part of the mesonephros grow rapidly in length forming secondary and tertiary infoldings. The nephrons situated ventrally are segmentally arranged in planes perpendicular to the long axis of the organ, whereas the dorsal nephrons are situated in various planes and their tubules are folded within narrow spaces of approximately ovoid form.Among the rae anomalies two-headed nephrons and nephrons lacking the main flexures are described.     

Organ renewal and cell divisions by differentiated cells in Drosophila

For many organs, the processes of renewal and regeneration recruit stem cells to replace differentiated, postmitotic cells, but the capacity of an organ's differentiated cells to divide and contribute is uncertain. Most cells of the Drosophila adult are the descendants of dedicated precursors that divide and replace larval cells that are histolyzed during metamorphosis. We investigated the provenance of cells that reconstitute the second thoracic metamere of the tracheal system (Tr2). These cells contribute the precursors for Branchless(FGF)-dependent growth of the dorsal air sacs, the major tracheal organs of the adult fly. We found that, in contrast to the cells in other tracheal metameres that proceed through many cycles of endoreplication, the cells that constitute the Tr2 branches in young larvae do not. Like the cells in other tracheal metameres, these cells arrest mitotic cycling in the embryo and form differentiated, air-filled tracheal branches of the larva. We report here that they reinitiate cell divisions during the third instar (L3) to increase the Tr2 population by ≈10-fold with multipotent cells.     

Vertebrate Claudin/PMP22/EMP22/MP20 family protein TMEM47 regulates epithelial cell junction maturation and morphogenesis

Background: TMEM47 is the vertebrate orthologue of C. elegans VAB‐9, a tetraspan adherens junction protein in the PMP22/EMP/Claudin family of proteins. VAB‐9 regulates cell morphology and adhesion in C. elegans and TMEM47 is expressed during kidney development and regulates the activity of Fyn. The conserved functions of VAB‐9 and TMEM47 are not well understood. Results: expression of TMEM47 in C. elegans functionally rescues vab‐9 mutations. Unlike Claudins, expression of TMEM47 in L fibroblasts does not generate tight junction strands; instead, membrane localization requires E‐cadherin expression. Temporally, TMEM47 localizes at cell junctions first with E‐cadherin before ZO‐1 colocalization and in polarized epithelia, TMEM47 colocalizes with adherens junction proteins. By immunoprecipitation, TMEM47 associates with classical adherens junction proteins, but also with tight junction proteins Par6B and aPKCλ. Over‐expression of TMEM47 in MDCK cells decreases apical surface area, increases activated myosin light chain at cell–cell contacts, disrupts cell polarity and morphology, delays cell junction reassembly following calcium switch, and selectively interferes with tight junction assembly. Reduced TMEM47 expression results in opposite phenotypes. Conclusions: TMEM47 regulates the localization of a subset of tight junction proteins, associated actomyosin structures, cell morphology, and participates in developmental transitions from adherens to tight junctions. Developmental Dynamics 245:653–666, 2016. © 2016 Wiley Periodicals, Inc.     

Amnioserosa development and function in Drosophila embryogenesis: Critical mechanical roles for an extraembryonic tissue

Despite being a short‐lived, extraembryonic tissue, the amnioserosa plays critical roles in the major morphogenetic events of Drosophila embryogenesis. These roles involve both cellular mechanics and biochemical signaling. Its best‐known role is in dorsal closure—well studied by both developmental biologists and biophysicists—but the amnioserosa is also important during earlier developmental stages. Here, we provide an overview of amnioserosa specification and its role in several key developmental stages: germ band extension, germ band retraction, and dorsal closure. We also compare embryonic development in Drosophila and its relative Megaselia to highlight how the amnioserosa and its roles have evolved. Placed in context, the amnioserosa provides a fascinating example of how signaling, mechanics, and morphogen patterns govern cell‐type specification and subsequent morphogenetic changes in cell shape, orientation, and movement. Developmental Dynamics 245:558–568, 2016. © 2016 Wiley Periodicals, Inc.