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At least 19 recordsLinked to original sources
PubMed2026

Admixture and Selection Driven by El Niño-Southern Oscillation Events Shape the Genetic Structure of Octopus mimus-O. hubbsorum Complex Across the Humboldt and South Equatorial Current Transition Zone.

Marine transition zones, where contrasting water masses converge, can function as natural laboratories for studying admixture and early stages of speciation. The genomic structure of the eastern Pacific Octopus mimus-O. hubbsorum complex was investigated by analyzing whole-genome sequencing data from 67 individuals sampled along the west coast of the Americas, spanning Mexico and the Peruvian coast. This includes the South Equatorial Current, the transition zone, and the Humboldt Current System. The mitochondrial genomes fell into two major genetic clades that largely corresponded to the warm-water northern (O. hubbsorum) and cold-water southern (O. mimus) lineages. Analyses of the nuclear genomes revealed the same bipartite structure but also identified a broad admixture zone characterized by two different admixed clades (Admixed-Cold and Admixed-Warm). The results suggest that episodic relaxation of oceanographic barriers during El Niño-Southern Oscillation (ENSO) events promotes secondary contact and gene flow, resulting in admixed individuals recurrently during ENSO years. However, the survival of these admixed individuals depends on the adaptive genetic composition of each organism and the prevailing environmental conditions. Outlier SNP analysis supports these findings, where the Admixed-Cold cluster shares mainly the adaptive genetic component identified as outliers in O. mimus, while Admixed-Warm is linked to those in O. hubbsorum. The O. mimus-O. hubbsorum complex is currently occupying a gray zone of speciation, in which selection and climate-driven connectivity act in tandem to shape genomic divergence.

gene flow↗
PubMed1992

The CNS-PNS transitional zone of the rat. Morphometric studies at cranial and spinal levels.

The transitional zone is that length of rootlet containing both central and peripheral nervous tissue. The CNS-PNS interface may be defined as the basal lamina covering the intricately interwoven layer of astrocyte processes which forms the CNS surface and which is pierced by axons passing between the CNS and PNS. Study of transitional zone development defines morphologically the growth, relative movement and interaction of central and peripheral nervous tissues as they establish their mutually exclusive territories on either side of the CNS-PNS boundary, and helps to explain the wide variations in the form of the mature transitional zone. Nerve rootlets at first consist of bundles of bare axons. These become segregated by matrices of fine Schwann cell processes peripherally and of astrocyte processes centrally. The latter may prevent Schwann cell invasion of the CNS. Astrocyte processes branch profusely and come to form the principal central nervous tissue component of the transitional zone. Developmental changes in the transitional zone vary markedly between nerves, reflecting differences in its final morphology. Widespread relative movements and migration of CNS and PNS tissues take place during development, so that the central-peripheral interface changes shape and position, commonly oscillating along the proximodistal axis of the rootlet. For example, developing cervical ventral rootlets contain a transient central tissue projection, while that of lumbar ventral rootlets and to a lesser extent that of cervical dorsal rootlets alternately increase and decrease in length. In the developing cochlear nerve, a central tissue projection is present before birth, but regresses somewhat before a marked outgrowth of central nervous tissue along the nerve takes place, which reaches into the modiolus during the first week postnatum. During development, some astrocytic tissue may even break off and migrate distally into the root, giving rise to one or more glial islands within it. During the period immediately preceding birth, Schwann cells come to be present in very large numbers in that part of the rootlet immediately distal to the CNS-PNS interface, the proximal rootlet segment. Here they form prominent sleeves or clusters of closely packed cells which intertwine with and encapsulate one another on the rootlet surface. Such Schwann cell overcrowding in the proximal rootlet segment could result in part from distal overgrowth of the rapidly expanding CNS around axon bundles, which might strip the Schwann cells distally off the bundle segments so engulfed.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Sonographic measurements of transition zone of prostate in men with and without benign prostatic hyperplasia.

Modern transrectal ultrasonography is a reliable means of visualizing the transition zone within the prostate gland. We measured the transverse, longitudinal, and anterior diameters and calculated the volume of the prostate and the transition zone in 400 patients. Ninety-seven patients with neither clinical nor sonographic evidence of benign prostatic hyperplasia (BPH) were compared with 108 patients with sonographically apparent BPH. The mean size of the transition zone was 6.14 +/- 3.2 g in the normal group and 24.81 +/- 14.4 g in the BPH group. The size of the transition zone increased significantly in relation to increased age of the patient. Ultrasonography allows accurate measurement of the transition zone and would be useful for documenting changes in the extent of BPH in response to therapy.

Adult↗
PubMed1978

The maturation of the ventral root-spinal cord transitional zone. An ultrastructural study.

Initially, ventral motoneurone axons in the transitional zone are closely apposed to one another. They subsequently become progressively separated by astrocyte processes which grow into the axon bundles. These processes become progressively more numerous and project into the ventral rootlet as a glial dome. This disappears with maturation, the surface of the transitional zone becoming level with that of the surrounding cord. At first, a considerable length of the axon in and deep to, the transitional zone is covered only by astrocyte processes. The sleeve of oligodendrocytic cytoplasm myelinating the axon extends distally along it towards the cord surface, thus decreasing the length of axon covered by astrocyte processes. Concurrently, the Schwann cell myelinating the most proximal peripheral internode becomes invaginated into the cord over lengths of 50 micrometer or more. Finger-like processes stem from its central end and abut on the nodal axolemma, as in peripheral nodes. However, a few astrocyte processes remain closely applied to the nodal axolemma, even at maturity. In the adult, the attachment zone consists of closely packed invaginations, each containing the central end of a Schwann cell and its myelin sheath, presenting a honeycomb appearance.

Age Factors↗
PubMed1990

Transmembrane assemblage of the photoreceptor connecting cilium and motile cilium transition zone contain a common immunologic epitope.

The photoreceptor connecting cilium bears a unique transmembrane assemblage which stably links cell surface glycoconjugates with the underlying axonemal cytoskeleton. Structural similarities between the photoreceptor connecting cilium and the transition zone of motile cilia suggests that this assemblage may also be present in motile cilia. Using a subcellular fraction enriched in detergent-extracted photoreceptor axonemes, three high molecular mass glycoconjugates (425, 600, and 700 kD) were previously identified as potential components of the assemblage. Through oligosaccharide characterization and binding of a specific monoclonal antibody, we have verified the localization of the 425 kD glycoconjugate to the transmembrane assemblage. Binding of the lectin peanut agglutinin (PNA) to the 425 kD glycoconjugate on nitrocellulose blots, and to isolated detergent-extracted axonemes, was assessed following treatment with the enzymes neuraminidase and O-glycanase. Changes in binding to the 425 kD glycoconjugate precisely paralleled changes in binding to intact axonemes, supporting the hypothesis that the 425 kD glycoconjugate is a component of the transmembrane assemblage. Furthermore, the results suggest that the 425 kD glycoconjugate contains sialated galactose-N-acetylgalactosamine oligosaccharides which are O-linked to the protein backbone. To directly assess the distribution of the 425 kD glycoconjugate, we produced a monoclonal antibody directed against this glycoconjugate. The antibody, K26, recognizes only the 425 kD on transblots of the axoneme fraction. K26 immunoreactivity of intact axonemes is identical to that seen by PNA staining. K26 staining of isolated photoreceptors and whole retina is uniquely localized to the region of the connecting cilium. Thus, in the photoreceptor, the 425 kD is not only a component of the transmembrane assemblage but is also completely restricted to the connecting cilium. Based on morphological similarities, the photoreceptor connecting cilium is thought to be homologous to the transition zone of the motile cilium. As such, we have stained oviduct epithelium with the K26 monoclonal antibody. Immunoreactivity is restricted to the region of the transition zone at the base of motile cilia.

Animals↗
PubMed1978

The anal transitional zone. A method for macroscopic demonstration.

The anal canal extends from the upper to the lower border of the internal sphincter. The canal can histologically be divided into three zones according to the epithelial lining, being of colo-rectal type in the upper part and squamous in the lower part, while the middle part, where the epithelium varies, is called the anal transitional zone (ATZ). This zone can be demonstrated macroscopically using whole mount staining with Alcian dyes, which reveal it as light green or blue, contrasting to the dark stained rectal type mucosa above and the unstained squamous epithelium below. Comparison with histological section shows that this zone corresponds with reasonable accuracy to the anal transitional zone.

Anal Canal↗
PubMed1975

The sensory cilium of retinal rods is analogous to the transitional zone of motile cilia.

The connecting cilium of rat retinal rods was studied by freeze-fracture and thin-sectioning techniques. Transverse strands of intramembranous particles could be observed on fracture face B on the ciliary plasma membrane. The strands were essentially similar to those found at the transitional zone of motile cilia ("ciliary necklace"). The larger number of intramembranous particles obscured the pattern on fracture face A of the membrane. On longitudinal sections of the cilia, beads showing a periodicity similar to the necklace strands were observed. Each bead consisted of two structures apposed to both sides of the plasma membrane. Transverse sections of the cilia revealed radial Y-shaped structures that connected each ciliary doublet with the plasma membrane. Axial tubules, central sheath, radial spokes and dynein arms were missing in the connecting cilium. Comparing the fine structure of the retinal cilia with that of motile cilia it becomes evident that the connecting cilium is analogous in structure with the transitional zone of motile cilia. The present observations suggest that periodic membrane beads along the plasma membrane on thin sections correspond to strands of necklace particles as observed on freeze-fractured membranes. The arrangement of the particles in transverse strands is probably ensured by the radial connecting structures.

Animals↗
PubMed1979

The anal transitional zone. Location and extent.

The location and extent of the anal transitional zone (ATZ) were investigated in the age group typical for anal canal carcinomas. The methods used were macroscopic determination after whole-mount staining with Alcian-dyes as well as conventional histological technique. The results show that the epithelial variants may be found over a larger area than previously reported, namely from 6 mm below to 20 mm above the dentate line. Variations in location and extent of the ATZ are described, as well as the frequent finding of mature squamous epithelium high in the anal canal. The significance of the findings in relation to the special types of anal canal carcinomas is discussed, and on the basis of the macroscopic definition of the canal, as well as the histological observations in this study, it is proposed that anal canal carcinomas should be defined as tumours partly or totally located within a distance of 2 cm above the dentate line.

Adenocarcinoma↗
PubMed2026

A transition zone enriched WIF1+ basal cell subtype is associated with benign prostatic hyperplasia.

The cellular composition and disease susceptibilities of the distinct zones of the human prostate remain incompletely understood. Benign prostatic hyperplasia (BPH) is a common condition that causes widespread morbidity and is nearly exclusively localized to the transition zone (TZ). Through extensive single-cell RNA sequencing (scRNA-seq) of benign regions from prostatectomy specimens, we identified a basal cell population expressing WIF1, VCAN, and NRG1, among other genes, that was significantly enriched in the TZ. Analysis of previously published scRNA-seq datasets further confirmed that WIF1+ basal cells were significantly enriched in BPH compared with normal prostate. Pathway and cell-cell communication analyses revealed that this basal subtype is associated with programs related to cell proliferation, epithelial-mesenchymal transition, immune regulation, angiogenesis, and hormone response. Together, the molecular signature, zonal distribution, and pathway enrichment suggest that TZ-enriched WIF1+ basal cells may contribute to BPH pathogenesis by promoting epithelial and stromal remodeling. © 2026 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

NRG1↗
PubMed1979

Fine structure of the transitional zone of the rat seminiferous tubule.

An electron microscopic study was made on the structure of the testicular transitional zone (TZ) in the adult rat. The TZ proper consists of modified Sertoli cellss, with only a few spermatogonia and macrophages, surrounding distally a very narrow lumen. The TZ Sertoli cells have nuclei with a somewhat coarser matrix and more peripheral heterochromatin than Sertoli cell nuclei of the nearby seminiferous tubules, and the electron density of the cytoplasm varies from cell to cell. Smooth endoplasmic reticulum is abundant, but usually there are also scattered ribosomal rosettes and an occasional profile of rough endoplasmic reticulum. Microtubules are very numerous in the columnar portion of the cell, and laminar structures seemingly joining the cell surfaces are sometimes seen. Lipid droplets and lysosmal structures are frequent cellular components in proximal TZ Sertoli cells. Empty intracellular vacuoles are abundant, sometimes arranged around areas of smooth endoplasmic reticulum. Occasionally, membrane-limited fine granules and vacuoles are seen within Sertoli cells and also in the TZ lumen, suggesting a possible secretory activity by these cells. The apical processes of the Sertoli cells form large vacuolar structures, and in the basal parts of the epithelium vacuoles with capillary-like appearance are frequently seen. Phagocytosis of germinal cells by the Sertoli cells occurs in the proximal region of the TZ. Round waste bodies in contact with the Sertoli cell apices protruding into the tubulus rectus, are also common. The tunica propria of the TZ is thickened and somewhat wrinkled, and in the proximal region the myoid cell layer loses its continuity and is replaced by fibroblasts. The epithelium of the tubulus rectus adjacent to the TZ consists of several overlapping epithelial cells. The typical junctional complexes between TZ Sertoli cells appear to be impermeable to the lanthanum tracer.

Animals↗
PubMed1991

[The transition zone of the central nervous system-peripheral nervous system of the adult rat; ultrastructural and immunocytochemical studies: a new function of the astroglia?].

At the transition between central nervous system (CNS) and peripheral nervous system (PNS), the CNS compartment forms cone-shaped incursions into the peripheral part of the dorsal root. The ultrastructural study of the CNS-PNS transitional zone shows that this region is particularly rich in astrocyte processes. In an attempt to investigate the possible role of the CNS-PNS interface astrocytes in myelin formation, a photonic microscopy immunocytochemical study has been done with anti-GFAP and anti-MBP sera. The CNS glial expansion shows an important GFAP immunoreactivity with intimate association between astrocyte processes and myelinated axons. This may indicate that the transitional myelin originates from astrocytes. The same region is also MBP-positive. Two explanations are considered: some astrocytes form transitional myelin sheathes and express MBP epitopes, or oligodendrocytes, with cell bodies distant from the CNS-PNS interface, send myelinating cytoplasmic expansions which are not shown by the techniques we used.

Animals↗
PubMed1990

Clear-cell carcinoma of the anal canal: a variant of anal transitional zone carcinoma.

Optically clear cytoplasm in tumor cells in the absence of mucin is most often associated with renal cell carcinoma. However it is important to recognize the rare occurrence of "clear-cell" variants among tumors arising in other sites. This report describes a clear-cell carcinoma arising in the transitional zone of the anal canal.

Adenocarcinoma↗
PubMed1992

Axo-glial interactions at the dorsal root transitional zone regulate neurofilament protein synthesis in axotomized sensory neurons.

After dorsal root crush, dramatic ultrastructural differences are observed between regenerated dorsal root axonal endings that are physically blocked at a ligation neuroma and those that are allowed to form axo-glial endings among the astrocytes at the dorsal root transitional zone (DRTZ). Physically blocked axonal endings swell immensely with membranous organelles and neurofilaments (NFs) while axo-glial endings do not, suggesting that DRTZ astrocytes stop axonal growth by activating a physiological stop pathway within those endings. Since protease-dependent NF degradation at axonal endings is a part of this pathway, this study addresses the question of whether NF subunit synthesis in the dorsal root ganglion (DRG) is regulated by the pathway. Lumbar dorsal roots were crushed and, at various postinjury times, the attached DRGs were removed and pulse-labeled in vitro with 35S-methionine for subsequent analysis of protein synthesis by electrophoresis and fluorography. Within 24 hr of axotomy, there was a down-regulation of the 68 kDa (NF-L) and 145 kDa (NF-M) NF subunits. At 14 d postcrush, a time when most of the regenerating axons have reached and been stopped by DRTZ astrocytes, NF protein synthesis returned to control levels. By contrast, when the axons were prevented from reaching the DRTZ by ligating or removing segments of the roots, NF synthesis failed to return to normal levels. These data suggest that activation of the physiological stop pathway by DRTZ astrocytes regulates NF protein synthesis in the DRG.

Animals↗
PubMed1979

Rapid change of chromomeric and pairing patterns of polytene chromosome tips in D. melanogaster: migration of polytene-nonpolytene transition zone?

The high variability of chromomeric patterns in near-terminal regions of polytene chromosome arms has been explored in a number of races, strains and hybrids of Drosophila melanogaster. Traditional explanations for tip differences between strains (differential compaction of chromatin, somatic or germinal deletion) are examined and, in the light of the reported observations, rejected. The range of polytene tip variability and rates of change in wild races are greater than has been supposed: strains formerly considered to be terminally deleted appear to gain terminal bands; others, formerly considered normal, appear to have lost them. Strains with high cell-to-cell tip variability are also described. Cell-to-cell variations, as well as much of the observed rapid changes in tip appearance, are probably due to heritable differences in the location of an abrupt transition zone between polytene and nonpolytene chromatin. A quantitative relationship between the amount of certain subterminal bands present and the frequency of tip association of nonhomologous chromosomes is shown and its possible significance for chromosome is shown and its possible for chromosome pairing discussed.

Animals↗
PubMed1978

Nanosecond relaxation processes of phospholipid bilayers in the transition zone.

Ultrasonic relaxation spectra of dipalmitoyl lecithin vesicles have been recorded as a function of temperature over the frequency range 14-265 MHz. A relaxation process is observed with a time constant of about 10(-8) sec. At the mid-point of the crystalline-liquid crystalline transition (about 41.3 degrees), the relaxation amplitude is maximal. This suggests that the relaxation process is intimately associated with the order-disorder transition. Further support for this conclusion comes from the finding that the volume change of the reaction, as calculated from the relaxation amplitude at the transition midpoint, agrees with that determined independently by equilibrium dilatometry measurements of the deltaV of the transition. The results show that a major step in the transition occurs on a far shorter time scale than previously recognized. Similar fast processes have also been detected in dimyristoyl and distearoyl lecithin vesicles. From a consideration of various lines of evidence, it appears that the relaxation monitors the elementary step associated with the isomerization of lipid chains, such as kink formation through internal bond rotations, as the bilayer transforms between ordered and disordered phases.

Chemical Phenomena↗
PubMed2025

Coupling of spectroscopy and nitrogen-oxygen isotopes unveils the mechanisms of dissolved organic matter and nitrate pollution in lakes within the agro-pastoral transition zone.

Lakes in arid and semi-arid regions are subjected to severe ecological stress, such as organic pollution, eutrophication, and salinization, due to climate change and human activities. This study investigates Chagannur Lake, a typical arid-region lake that is representative and ecologically sensitive in Northern China's agro-pastoral ecotone, to uncover its pollution characteristics and mechanisms. We employed fluorescence spectroscopy and stable isotope analysis to trace dissolved organic matter (DOM) and nitrate sources. The DOM composition was dominated by microbial metabolic byproducts and protein-like substances, suggesting that microbial processes are key to organic matter transformation. Source apportionment revealed that pollutants primarily originated from livestock and poultry manure (37.6 %), agricultural fertilizers (35.6 %), and soil erosion (24.7 %), with agricultural fertilizers contributing most significantly in the Gogstai River (63.3 %). A structural equation model (SEM) coupling spectral and mass spectrometric data revealed that microbial transformation significantly impairs the lake's self-purification capacity, thereby promoting pollutant accumulation (path coefficient = 0.91,*p < 0.05). Moreover, microbial processes link endogenous and exogenous pollution, a mechanism effectively traced by isotopic and fluorescence indices (path coefficient = 0.55, &#x204e;&#x204e;p < 0.01). These findings enhance the understanding of pollution sources and transformation mechanisms in arid-region lakes and offer foundational theoretical support for policymakers engaged in pollution control strategies.

Lakes↗
PubMed1991

The ultrastructure of the transition zone between specialized cells ("Flügelzellen") of Huxley's layer of the inner root sheath and cells of the outer root sheath of the human hair follicle.

We studied biopsy specimens taken from the scalp of four normal volunteers by transmission electron microscopy (TEM). At the suprabulbous level of the follicle, where the cells of Henle's layer are fully keratinized but the cells of Huxley's layer are not, the cytoplasmic processes of Huxley's layer ("Flügelzellen") reach the cells of the outer root sheath through the keratinized cylinder of Henle's layer. This junction between the outer root sheath cells and the "Flügelzellen" has not been previously characterized ultrastructurally. It is peculiar in its total lack of desmosomes, and it may have the features of a gap junction. The function of this structure and its possible role in hair growth is unknown. It may be related to nutrition, differentiation, or both.

Adult↗