Proliferative Units Research Articles

Depositional Framework of Early Miocene (Fleming) Episode, Northwest Gulf Coast Basin: ABSTRACT

The Fleming Group and its basinward equivalents constitute deposits of a major Cenozoic depositional episode of the northern Gulf Coast basin. The facies complex is bounded by the Amphistegina B shale and below by the Anahuac shale. Initially, lower Miocene (Oakville) progradation built across the broad, submerged shelf platform constructed during the earlier Frio depositional episode. At the Frio paleocontinental margin, the rate of outbuilding slowed as large-scale growth faulting created a narrow lower Miocene expansion zone. The later part of the episode was characterized by a stable to retreating shoreline and consequent aggradational to retrogradational deposition (Lagarto formation). The lower Miocene depositional framework includes, in south Texas, the Santa Cruz fluvial system and the North Padre delta system. The bed-load fluvial complex fed a wave-dominated delta, constructing a broadly convex deltaic headland across the foundered Frio Norias delta system. Extensive wave reworking and longshore transport of sand and mud nourished a broad barrier/lagoon and strand-plain complex that extended along the central and much of the northeastern Texas coast. This well-known Matagorda barrier/strand-plain system was bounded updip by a coastal plain traversed by numerous small intrabasinal streams. Near the present Sabine River, westernmost deposits of a continental-scale, mixed-load fluvial and equivalent delta system extend beneath the Texas coastal plain and shelf fro the Miocene depocenter in Louisiana. Here, the initial phase of early Miocene progradation was also complicated by the incision and filling of numerous submarine gorges. Lower Miocene reservoirs have produced nearly 4 billion bbl of oil-equivalent hydrocarbons from nine identified plays in the Texas coastal plain and shelf. The most prolific play, the salt domes of the Houston embayment, accounts for most of the oil and more than two-thirds of the total production from the sequence. Four offshore plays offer the greatest discovery potential for substantial new reserves, primarily gas. To date, however, the yield per volume of reservoir sandstone for Miocene plays remains low, relative to more prolific units such as the Frio Formation. End_of_Article - Last_Page 1421------------

An autoradiographic study of the cell proliferation during involution of the rat pancreas.

After ligation of the rat pancreas, DNA synthesis in centoacinar cells and cells of the intercalary ducts, proximal and distal to the ligature, was suppressed for about 18 hr. This preceded a large increase in thymidine labelling of the nuclei of these cells. The increase in the thymidine indices was much greater and more prolonged in the distal pancreas where duct-like structures were formed that replaced the acini. DNA synthesis in acinar cells proximal to the ligature was suppressed for 36 hr preceding an increase in the thymidine indices much smaller than that in the duct cells. DNA synthesis in acinar cells distal to the ligature ceased and the acinar cells progressively died. We propose that the pancreas is composed of proliferative units, each comprising acinar cells, centroacinar cells and intercalary ducts, which react as a whole when acinar cell loss occurs in pathological processes.

Proliferative units in stratified squamous epithelium

Clinical and Experimental DermatologyVolume 8, Issue 1 p. 95-106 Proliferative units in stratified squamous epithelium W.J. HUME, W.J. HUME Paterson Laboratories, Christie Hospital and Holt Radium Institute Manchester M20 9BXSearch for more papers by this authorC.S. POTTEN, C.S. POTTEN Paterson Laboratories, Christie Hospital and Holt Radium Institute Manchester M20 9BXSearch for more papers by this author W.J. HUME, W.J. HUME Paterson Laboratories, Christie Hospital and Holt Radium Institute Manchester M20 9BXSearch for more papers by this authorC.S. POTTEN, C.S. POTTEN Paterson Laboratories, Christie Hospital and Holt Radium Institute Manchester M20 9BXSearch for more papers by this author First published: January 1983 https://doi.org/10.1111/j.1365-2230.1983.tb01749.xCitations: 19AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume8, Issue1January 1983Pages 95-106 RelatedInformation

New knowledge about the epidermis.

This article reviews recent advances in our understanding of epidermal cytoarchitecture and kinetics. Special attention is paid to the Epidermal Proliferative Unit, and to factors controlling epidermal cell turnover.

Genesis of the dorsal lateral geniculate nucleus in the rhesus monkey: Site and time of origin, kinetics of proliferation, routes of migration and pattern of distribution of neurons

AbstractAutoradiograms of the dorsal lateral geniculate body (LGd) in 2‐ to 3‐ month‐old rhesus monkeys, each of which had been exposed to a pulse of H3‐thymidine (H3‐TdR) on a specified embryonic (E) or early postnatal (P) day displayed heavily labeled neurons only in animals injected at E36, E38, E40 and E43. In animals exposed to H3‐TdR during the last four months of gestation or after birth, the LGd contained only an occasional labeled glial cell. In the monkey, therefore, all neurons destined for the LGd are generated during 8 to 9 days at the end of the first quarter of the 165‐day gestational period.An examination of embryos injected with H3‐TdR around E40 and killed one hour later showed that cells destined for the LGd are generated in two distinct proliferative tiers situated near the surface of the third ventricle. The inner 100‐to 150‐μ‐wide tier consists of pseudostratified columnar cells and corresponds to the ventricular zone. The outer, somewhat narrower tier has cytological features characteristic of the subventricular zone; this zone has not been described previously in the developing diencephalon.It was estimated that the approximately 1.7 × 106 neurons that will comprise the fully developed LGd on one side are derived from about 22,000 precursor neurons that are present in the proliferative sector on the corresponding side of the developing diencephalon at E35. The proliferative pool increase 10‐fold in cell number by E41 and becomes exhausted during E44. The number of postmitotic cells leaving the proliferative pool increases exponentially from 2,500 at E36 to a maximum of 350,000 at E43, and then sharply declines to zero by E45.Analysis of embryos exposed to H3‐TdR around E40 and sacrificed 3, 7, 14 or 42 days later indicate that following their last cell division, young neurons migrate laterally 500–700 μm to the outer aspect of the developing thalamus. Migrating neurons are deployed in distinct cellular fascicles that span the developing diencephalon from the surface of the third ventricle tot he pial surface. Several generations of neurons generated in a restricted location of the germinal zone (proliferative unit) appear to migrate along a single cellular fascicle and accumulate in a column‐shaped aggregate. Neurons generated earliest reach the outermost surface of the diencephalon; neurons generated later accumulate at progressively more inner positions and hence form an “outside‐to‐inside” gradient. The axis of the “outside‐to‐inside” gradient initially oriented latero‐medially later becomes oriented ventro‐dorsally. Thus, in the mature monkey, early generated neurons lie in the ventral magnocellular layers, whereas neurons generated later become part of the dorsal parvocellular layers. Despite these tectogenetic changes, the relationships between early and late generated neurons derived from the same proliferative unit remain preserved and eventually may establish a single “projection column.”

Distribution and morphology of UV-induced epidermal cell death

Epidermal cell ‘dyskeratosis’ that appeared after ultraviolet (UV) irradiation of mouse skin was found to be most marked during a time when kinetic studies showed there was complete suppression of epidermal cell proliferative activity. Sheet preparations of epidermis showed that ‘dyskeratosis’ affected basal cells in both the central and peripheral zones of individual epidermal proliferative units, and caused a marked reduction in the number of cells in this epithelial layer. Electron microscopy of the degenerate epidermal cells showed that they were keratinocytes that had undergone morphologically typical apoptosis, an ultrastructurally distinctive form of individual cell death characterized by both nuclear and cytoplasmic condensation and fragmentation. Most of these cell fragments were engulfed and degraded by adjacent surviving keratinocytes, but some were phagocytosed by Langerhans cells. It is suggested that apoptosis following UV irradiation occurs in cells that are unable to repair the genetic damage that is inflicted by this form of injury. Death occurring during mitosis, or as a result of accelerated differentiation, does not appear to be involved.

Epidermal Cell Production Rates

Labeling and mitotic index data and estimates for the length of the S and M phases of the cell cycle from the literature have been compared with new data obtained over a 24-hr period from various epidermal sites in mouse. It has been found that values obtained at a single time of the day may give misleading results. All data have been interpreted in terms of cell production rates per epidermal proliferative unit (EPU). The final conclusions after consideration of cell production rates, labeling and mitotic indices, epidermal transit times, and epidermal structure are that dorsal and ear skin have rather similar cell production rates while tail and foot rates are 4 to 7 times higher. A comparison has also been made between the mouse results and the available human data. Hairless mouse dorsum appears from structural and proliferative aspects to be the best model for some regions of human skin. A new model has been proposed for epidermal proliferation based on the EPU. The model suggests a role for the Langerhans cells and suggests that there is a program of sequential cellular maturity in the EPU originating at the level of a central basal stem cell through committed proliferative cells and ending with cell loss from the skin surface.

Control of Epidermal Proliferative Units (EPUs): An Hypothesis Based on the Arrangement of Neighbouring Differentiated Cells

A review of the data available on organisation in the differentiated compartment of epidermis has led to the formulation of a hypothesis. This suggests that some degree of control operates within neighbouring groups of epidermal proliferative units (EPUs) determining the input of cells to the highly ordered columns of cornified cells. It seems that this inter-unit control results in groups of units being in “synchrony”. It is obvious that some degree of intra-unit control also operates.

The fine structure and cell kinetics of mouse epidermis after wounding.

A variable amount of cornified tissue removed from mouse dorsal epidermis results in stimulation of the entire basal layer. Stimulation does not appear to be dependent on damage to an indiviaual epidermal proliferative unit (EPU). The immediate reaction to wounding is a rapid movement of cells from the basal layer to the differentiating compartment resulting in depopulation of the basal layer, which is followed by a burst in DNA-synthetic activity. The result of the increased transit of cells through the epidermis is that various aspects of keratinization can appear abnormal. The Langerhans cells show several changes, often appearing suprabasal and becoming smaller, rounded cells with a less-clear cytoplasm and fewer granules. The initial migratory reaction results in a largely normal epidermis on the third day. This reaction is followed by a transient hyperplasia which reaches its peak on the sixth to seventh day and gradually returns to normal by the fourteenth to fifteenth day. The hyperplasia is characterized by a loss of the ordered stacking of cornified cells which become shorter and thicker than normal. There is a return to the stacked state beginning on the tenth day. The Langerhans frequency is apparently at its lowest on days 6-7 when the proliferation levels are at their maximum. An inverse relationship appears to exist between relative Langerhans cell frequency and cell proliferation rate. The data suggest that the frequency of Langerhans granules also changes during the course of the hyperplasia, peak levels being observed just before the decline in proliferative activity.

Fine-structural identification and organization of the epidermal proliferative unit

ABSTRACT Mouse dorsal interfollicular epidermis has a vertical organization consisting of approximately 1400 units/mm2. Each unit is identified by its uppermost 4 to 6 layers of roughly hexagonal flattened cornified cells or squames, which are stacked in a precise vertical column. Beneath each column of squames there are 3 differentiating cells and a group of 10 or 11 basal cells, which provide cells to replace those lost by desquamation at the top of the squame column. The whole unit is termed an epidermal proliferative unit or EPU. In the central region of the basal layer of each EPU is a single dendritic Langerhans cell, devoid of desmosomes, but held in position by the surrounding keratinocytes. The dendrites radiate outwards between the keratinocytes to the periphery of the unit. Keratinocyte migration into the spinous layer takes place from the edge of the unit. In the squame column itself, a modified cell-to-cell attachment (squamosome) runs around the edge of each cornified cell, and attaches it to the overlapping region of cells from adjacent squame columns.

The epidermal proliferative unit: the possible role of the central basal cell.

ABSTRACTA model is suggested for the organization of the epidermis based on the ordered structure of the differentiating layers, as demonstrated by published work. This ordered structure enables one to look through the epidermis at the basal cell nuclei and to see their arrangement beneath the differentiating column of cells. In dorsal skin from male DBA‐2 mice there are 10.6 basal nuclei beneath a column of cells. The central nucleus of the group responds slightly earlier and more effectively than the rest to stimulation, is cycling more slowly than the majority of the basal nuclei and may spend significant periods of time out of cycle.The skin appears to contain a series of fairly independent proliferative units, each of which contain ten or eleven basal nuclei and eight to ten superficial cells of which only the youngest one or two retain their nuclei. At the centre of each group of basal nuclei is a cell that behaves differently from the rest and which is present in the skin in numbers compatible with the number of clonogenic cells. It is suggested that this represents the basic stem cell of the unit.

An estimation of proliferative population size in stomach, jejunum and colon of DBA-2 mice.

ABSTRACTLiquid scintillation and autoradiographic techniques have been used to provide quantitative data on the proliferative units, the crypts, of stomach, jejunum and colon of DBA‐2 mice. A slight modification of the crypt squash technique has provided data suggesting that about 50% of the cells of the jejunal crypt are at any given time in the proliferative state. This value is lower in the colon while in the stomach glands only 20% of the cells are involved in cell production. The data provide estimates for cell cycle times of 26·3, 16·0 and 23·2 hr for stomach, jejunum and colon respectively.The size and number of proliferative units have been determined for three regions of the gastrointestinal tract of mice. A review of the literature suggests that considerable strain differences may exist.