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At least 19 recordsLinked to original sources

PubMed1975

The "imaged-desmosome": a component of intercalated discs in embryonic guinea pig myocardium.

A heretofore undescribed structural variation of the desmosomes of the intercalated disc is found in myocardial cells of the embryonic guinea pig. These desmosomes consist of the usual pair of opaque leaflets, each of the pair contributed by one of the apposed muscle cells. In addition, in the cytoplasm of one of the cells there appears a pair of linear densities (facsimile-lines) parallel to the nearest desmosomal plaque and separated from it by a 60 mm space. The facsimile lines superficially resemble the desmosomal leaflets in length and thickness, thus forming a cytoplasmic "image" of the desmosome. These "imaged-desmosomes" are found predominantly in the longitudinally-running portions of the intercalated discs and are common in 7-week embryos. Their incidence drops sharply by eight weeks of gestation, and they are virtually absent from the heart of the newborn animal. Often tubules of the sarcoplasmic reticulum (SR) are found in apposition to the facsimile-lines; thus it appears that association of SR tubules with desmosomes is responsible for the formation of imaged-desmosomes.

Animals↗

PubMed1992

Conjoined twins: theoretical embryologic basis.

A theoretical basis for the embryology of conjoined twins was formulated from clinical experience with ten cases and extensive review of pertinent embryologic and clinical literature, including over 500 cases. Regarding the age old question of fusion or fission, it is concluded that there is no known embryologic process by which conjoined twins can be formed by fission but firm evidence to support fusion in all cases. Whether the fusion occurs between embryos on one embryonic disc or on two is of no consequence since they are all monovular. Intact ectoderm will not fuse to intact ectoderm, and all seven types of conjoined twins are explained by seven possible sites of union in the early embryo. One new term is proposed: parapagus, from the Greek para, meaning "side," combined with pagus, meaning "fixed"; this is the group formerly called dicephalus or diprosopos. These anterolaterally united parapagus twins must result from two nearly parallel notochords in close proximity; craniopagi and pygopagi from fusion at the cranial and caudal neuropores, respectively; cephalopagi and ischiopagi from union at the pharyngeal and cloacal membranes, respectively; thoracopagi from merging of the cardiac anlage; and omphalopagi from fusion of the umbilicus or of the edges of two embryonic discs in any area not including the above sites. Parasitic twins result from embryonic death of one twin, leaving various portions of the body vascularized by the surviving autosite. The rarity of cases (2) not easily explained by the above theories, and the nearly 6% of twins with two umbilical cords arising from the placenta would seem to support these conclusions. Should one wish to learn the methods of a conjurer, he might vainly watch the latter's customary repertoire, and, so long as everything went smoothly, might never obtain a clue to the mysterious performance, baffled by the precision of the manipulations and the complexity of the apparatus; if, however, a single error were made in any part or if a single deviation from the customary method should force the manipulator along an unaccustomed path, it would give the investigator an opportunity to obtain a part or the whole of the secret.(ABSTRACT TRUNCATED AT 400 WORDS)

Humans↗

PubMed1978

Growth, protein content and distribution of early pig embryos.

Development of porcine conceptuses included transitions of five stages: blastocysts of spherical, ovoid, and tubular forms containing an embryonic disc and trophoblast, extremely elongated filamentous blastocysts, and stages of embryogenesis between days 9 and 18 after mating. Embryonic survival was reduced by 17% during this period. In this litter-bearing species, intense alteration in distribution patterns occurred at days 11 and 12, when blastocysts rapidly elongated to filamentous forms. Increased embryo mortality did not result from rapid changes in distribution patterns of conceptuses within the same uterine horn at this time. Filamentous blastocysts quickly reached lengths often exceeding 60 cm, and these conceptuses became regularly spaced with no overlap of tubular membranes from other embryos in that horn. The number of conceptuses within a uterine horn ranged from 1 to 13. Protein in individual conceptuses was used as an indicator of growth and denoted exponential increase, but at a lower rate for blastocysts of spherical, ovoid, and tubular forms as compared with that found in filamentous blastocysts and embryogenesis stage conceptuses. Growth on a conceptus, based upon its protein content, was independent of the developmental stage or potential loss of those neighbors nearest that conceptus.

Animals↗

PubMed1975

Early embryology and implantation in the California leaf-nosed bat, Macrotus californicus.

Female reproductive tracts from 84 bats were examined by light and/or electron microscopy to electron microscopy to observe early embryology and implantation in Macrotus. The earliest pregnancy was observed in October and by the end of October all bats were pregnant. Implantation had begun in most specimens from late October. In late November females were carrying implanted blastocysts in which differentiation of endoderm was noted. Reichert's membrane was first observed in November. In early December the trophoblast had begun to differentiate into cytotrophoblast and syncytiotrophoblast and by the end of January this differentiation was most evident. Reichert's membrane persisted until late January. Endoderm in the January sample completely surrounded the yolk sac cavity. By late February the embryos were at the embryonic disc stage had differenitated mesoderm. The uterine-fetal relationship was complex and an early placenta was recognized. In late March the embryos spanned a range of development from neural plate to limb-bud stages. Parturition occurred in June. This lengthy gestation period is characterized by an embryonic diapause of approximately four and one-half months. The roles of food supply and/or temperature in controlling this growth rate and the evolutionary implications of this development are discussed.

Amnion↗

PubMed1992

Bovine embryos produce a urokinase-type plasminogen activator.

The type of plasminogen activator (PA) secreted by bovine embryos was identified. Day 12-14 embryos were collected from estrus-synchronized, superovulated, and naturally mated crossbred beef cows. Embryos were left intact (E) or microdissected into component embryonic discs (ED) and trophoblastic vesicles (TV). Intact embryos, ED, and TV were pre-cultured for 2 days in Minimum Essential Medium Alpha (MEM alpha) with 10% heat-inactivated fetal calf serum, washed in serum-free MEM alpha, and cultured individually for 5 days in 50 microliters microdrops of MEM alpha with 15 mg/ml bovine serum albumin. At 24 hr intervals, E, ED, and TV were observed for tissue morphology and transferred to fresh microdrops, and medium was recovered and frozen at -20 degrees C. At the end of culture, blastocoelic fluid (BF) and embryonic tissues were recovered and frozen at -20 degrees C. Plasminogen activator concentrations in medium, tissues, and BF were determined by using a caseinolytic assay. Antibodies to urokinase-type PA (anti-uPA) and tissue-type PA (anti-tPA), and the urokinase inhibitor, amiloride (AMR), were used to identify the type of PA produced by bovine embryonic tissues. Intact embryos and TV released more PA (P less than 0.05) than ED, and tissues exhibiting expanded blastocoels released less PA (P less than 0.05) than tissues with collapsed blastocoels. Blastocoelic fluid from TV exhibited more PA (P less than 0.05) activity than from ED. Treatment with anti-uPA decreased PA activity (P less than 0.05) in pooled medium and tissues from E compared to treatment with nonspecific immunoglobulins and anti-tPA.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride↗

PubMed1975

The development of primordial and definitive amniotic cavities in early Rhesus monkey and human embryos.

Re-examination of early rhesus monkey and human embryos in the collection of the Carnegie Institution of Washington suggests that the mechanism of amniogenesis in both is basically similar to that of the hedgehog and vespertilionid bats. A primordial amniotic cavity develops by cavitation within the embryonic mass of 10-day rhesus monkey, and 7-day human, blastocysts. This primordial cavity has no relationship initially with the overlying trophoblast, contrary to earlier reports. Subsequently, there is a thinning and peripheral spreading of the epiblastic roof of the primordial cavity, resulting in partial opening of the roof and formation of a slightly cupped embryonic disc. The resulting space is not homologous with the primordial amniotic cavity; instead, it is a transitory tropho-epiblastic cavity. The definitive amniotic epithelium forms by the upfolding and mitotic proliferation of the margins of the epiblastic disc; this process is completed in 11-day rhesus, and 9-day human, blastocysts. Amniogenesis by cavitation is associated with the persistence of polar trophoblast following implantation, and it is suggested that this cavitation process may be essential for providing a free epithelial surface for the morphogenetic movement of epiblastic cells during subsequent formation of the primitive streak.

Amnion↗

PubMed1978

The ovoimplantation of Microcebus murinus Miller. (Primates, Lemoruoidea, Strepsirhini).

The process of nidation of Microcebus murinus may be subdivided into several stages (preadhesion, apposition, attachment and invasion), as is indicated for protracted phases of preimplantation. Not until the apposition stage does the inner cell mass orient itself orthomesometrially, while concurrently a nidation plaque develops in the abembryonal trophoblast that overlies and resorbs the coalescent glands. During the subsequent adhesion stage, the paraembryonal, bilaminar omphalochorion becomes attached to the uterine epithelium, with focal resorption of the latter. In addition, chorionic vesicles begin to develop. In the meantime, the embryonic disc has lost its trophoblastic cover as a preliminary to the formation of the pleuramnion. The formation of a nidation plaque, together with the subsequent central implantation of Microcebus, suggests a close relationship to Loris tardigradus, characterizing the mode of implantation of Strepsirhini. The nidation plaque and its invasive capacity, giving rise to a syndesmochorial placental nucleus, provide a placentological link to Galago demidovii.

Animals↗

PubMed1979

Morphogenesis of the fetal membranes of an American mole, Scalopus aquaticus.

Scalopus membranes are characterized by: Superficial nidation; antimesometrial orientation of the embryonic disc; amniogenesis by folding; an extensive but transitory choriovitelline placenta; a large yolk sac with late and incomplete inversion; large persistent allantoic vesicle; a very broad, thin, villous, epitheliochorial chorioallantoic placenta of annular shape interrupted mesometrially, dotted with numerous areolae, and bordered by a nonvillous sparsely vascular chorioallantoic membrane connected with the persistent bilaminar omphalopleure by a very narrow rim of chorion. There is no decidua. Electron microscopy shows that at 8 mm, CR, (limb bud embryo) the uterine epithelium of the interhemal membrane may be 0.5 micron or less in thickness, but that it shows no signs of degeneration. Trophoblastic microvilli often penetrate the epithelium to within 0.2 micron of its base. At this time there is active secretion by the uterine glands, and cellular hypertrophy and cytolysis of the epithelium at the gland mouths, with active phagocytosis by the areolar cytotrophoblast. The occurrence of absorptive areolae in an insectivore emphasizes the probable primitiveness of this widely distributed placental mechanism. In spite of similarities of the yolk sac to that of rabbits and rodents, the bilaminar omphalopleure produces no invasive trophoblastic giant cells. The definitive membranes of Parascalops breweri and Scapanus latimanus are like those of Scalopus. The placentae of Talpa europaea, Condylura cristata, and Neurotrichus gibbsii are discoid and relatively much smaller, thicker and more complex in internal structure. There is some reason to believe that the fetal membrane systems of moles and shrews (Soricoidea) are more like those of the ancestral mammalian stock than are those of any other recent eutherians.

Animals↗

PubMed1979

The initial development of the human brain.

An account of the early development of the human brain has been prepared from the data available for the Carnegie Collection, as well as from published information from other sources. Although the site of the neural plate can be discerned at stage 7, the first visible indication of the nervous system is the neural groove in certain embryos of stage 8, in which the embryonic disc measures more than 1 mm and the notochordal process at least 0.3 mm. The progressive fusion of the neural folds during stage 10, and the closure of the rostral and caudal neuropores at stages 11 and 12, respectively, are detailed with further precision than hitherto. It is emphasized that the major subdivisions of the human brain do not begin as vesicles, but as enlargements of the open neural folds at stage 9. The relationships of the neuromeres to the otic region, the somites, and the neural crest are clarified and illustrated. The early appearance of the telencephalon medium (before cerebral vesicles have formed) is stressed, and the terminological implications for the subdivisions of the brain are discussed.

Brain↗

PubMed1975

Neuroectodermal origin of avian hypothalamo-hypophyseal complex: the role of the ventral neural ridge.

Embryonic discs from White Leghorn chick embryos (presomite to 12-omite stages) were examined in serial transverse and longitudinal sections. Later stages, up to 21 days, were also examined. The following observations were made: (1) Lateral folding rather than head folding is the mechanism by which the avian embryo is delimited. The process takes place at two terminal points, one cephalic the other caudal. (2) Thickening of the ventral ectoderm around the tip of the presumptive anterior neuropore, beginning at the 4-somite stage, subsequently extends the dorsal neural ridge to form a ventral neural ridge. (3) The cephalic portion of the ventral neural ridge, extending from anterior neuropore to optic chiasma, is mainly incorporated into the alar plates of the diencephalon. (4) The caudal portion, extending from optic chiasma to the stomodeum, gives rise to Rathke's pouch and thus to the adenohypophysis. We conclude that the latter is to be regarded as of neuroectodermal rather than ectodermal (stomodeal) origin, and that some or all of the neuroendocrine nuclei of the hypothalamus are similarly derived from the neuroectoderm of the neural ridge. The hypothalamo-hypophyseal complex is thus to be regarded as a single rather than a composite entity.

Animals↗

PubMed1979

An analysis of implantation in Indian hipposiderid bats.

The meagre information on the early developmental stages and the evolutionary and taxonomic position of hipposiderid bats has stimulated the present study. The cranial segment of the uterus forms a balloon-like enlargement at the time of implantation, and the antimesometrial part of its huminal slit expands into a spacious implantation chamber. Implantation is superficial and circumferential and the embryonic disc is orientated towards the side of the uterus which lies between the lateral and the antimesometrial sides. Reichert's membrane develops early, and the formation of a symplasma is described. A comparative account of implantation in the four species of hipposiderid bats of the family Hipposideridae is given, and the taxonomic position of this family is discussed on the basis of the present observations and earlier work on the embryology of Chiroptera.

Animals↗

PubMed1978

Developemnt of the human optic disc: light microscopy.

Human embryonic and fetal optic discs were studied in semi thin sections stained with silver and toned with gold, in a series ranging from 7 to 21 weeks of gestation. The observations suggest that Bergmeister's papilla forms by proliferation of glial cells in the optic disc rather than by sequestration of retinal glia by axons growing through the region. A possible stimulus for such a glial proliferation is hypothesized to be traction on the anterior face of the disc exerted through the primary vitreous. The formation of the glial sheath of the hyaloid artery also appears to be a consequence of traction from the primary vitreous.

Fetus↗

PubMed1975

Induced RNP production in different cell types of Drosophila.

The typical RNP complexes produced in puff 2-48BC in the salivary gland chromosomes as a consequence of treatments interfering with the cellular respiratory metabolism have been found in various other cell types after treatment with 5-10- minus 2 M vitamin B6 for 4 hr. In Drosophila hydei the typical RNP complexes were present in puff 2-48BC in the nuclei of gastric caeca cells, in nuclei of cells of the imaginal (wing) discs and embryonic cells in primary culture. Similar RNP complexes were observed in a puff in D. virilis salivary gland nuclei, but not in salivary gland nuclei of D. melanogaster.

Animals↗

PubMed2026

Developmental origins of pregnancy loss in cattle.

Pregnancy losses constitute a major economic burden in cattle farming and are caused by developmental failures occurring mostly during the first month of gestation. This review integrates knowledge gathered from direct and indirect estimations of embryo survival at critical developmental periods with knowledge obtained from functional in vivo and in vitro studies to elucidate the developmental origins of pregnancy loss in cattle. Fertilization failures and embryonic arrest prior to the blastocyst stage, estimated based on morphological observation of flushed structures, average 10 to 20 and 10 to 30%, respectively. Reduced oocyte competence arises as the major driver of the underlying developmental failures, including impaired embryonic genome activation, loss of totipotency and defective first lineage differentiation. To estimate embryonic losses from blastocyst to implantation, direct observation of embryo development and indirect proxies of pregnancy have been employed. Indirect proxies such as nonreturn to oestrus or biochemical markers such as Interferon Stimulated Genes or Pregnancy Associated Glycoproteins inform on the development of extra-embryonic membranes, but do not distinguish between viable pregnancies and anembryonic pregnancies, where embryo-devoid structures formed by extra-embryonic membranes are able to maintain the corpus luteus to day 37. Merging data from recovery rates of early elongated structures and incidence of embryo-devoid structures, embryonic mortality from blastocyst hatching to pregnancy recognition oscillates between 12-79% for in vivo derived and 40-86% for in vitro produced embryos. The exclusion of anembryonic pregnancies diminishes embryonic mortality between day 16 and the time when the embryo proper is clearly identifiable by ultrasound (days 31-42) to less than 10%. The manuscript also provides an update on novel tools used to elucidate embryonic metabolic and signalling requirements, as well as on the molecular regulation of key developmental landmarks that must be achieved during developmental windows most susceptible to pregnancy loss.

cattle↗

PubMed1975

The articular disc of the hand.

The carpal articular disc have been studied in serial sectioned embryonal and fetal hands. It can be concluded that the articular disc is an extensive fibrous system that comes from the ulnar edge of the distal end of the radius and reaches, bordered by the deep layer of the antebrachial fascia, the base of metacarpal V. In this course, insertions take place into the ulnar aspect of the head of the ulna, into the ulnar styloid process and into the ulnar carpals. Emphasis has been laid upon the fact that the sheath of the m. extensor carpi ulnaris tendon is part of the fibrous system of the disc. The positions of the dorsal tendons seen with respect to the fascial implicate a mutual shift during pronation and supination of the hand. The relations between the so-called ligamentum subcruentum and prestyloid recess have been established, the presence of cartilaginous primordia in the developing dis has been discussed. We come to the conclusion that the evidence for drawing a parallel between phylogenetic and human embryological phenomena is still insufficient. In this connection we have stressed the modus of development of the pisotriquetral joint space.

Anatomy, Comparative↗

PubMed1975

[The development of the triangular ligament in man].

The origin of the carpal articular disc has been studied in serial sectioned embryonal and fetal hands. In particular the complex; ulnar styloid process--triangular disc--carpal joint has been considered. In this development a relation is brought about between the so-called lig. subcruentum and the prestyloid recess. It has to be emphasized, that both pre-styloid recess and pisotriquetral joint space originate as isolated spaces.

Carpal Bones↗

PubMed1992

What are and what are not imaginal discs: reevaluation of some basic concepts (Insecta, Holometabola).

Some general aspects of the concept of imaginal discs in the Holometabola are reevaluated. Their monolayer character and continuity with the surrounding epidermis are confirmed. Studies on the imaginal discs of the silkworm (Bombyx mori) and data from the literature show that the discs and their peripodial cells produce cuticle during larval life, as well as at metamorphosis. In B. mori it is demonstrated that adult and larval antennae are produced by the same cells or their progeny. The results also suggest that segments of the typically three-segmented larval antenna of Holometabola are not scape, pedicel, and one-segmented flagellum; at least segments 2 and 3 are of flagellar origin. Based on these and some additional facts it is argued that: (1) No larval organs are "replaced" at metamorphosis, but strict "sequential homology" is always maintained. (2) Imaginal discs are not undifferentiated structures destined to form the adult after larval breakdown, cannot be unambiguously defined, and do not represent qualitatively different epidermal structures. Classical imaginal discs (invaginated and present also in pre-final larval instars) arose several times independently and were not present in the larvae of ancestral Holometabola. (3) Since the disc cells are not undifferentiated and "embryonic" (if these words have a defined meaning at all), it is unreasonable to expect that the processes taking place in discs at metamorphosis would differ fundamentally from those occurring in other diploid metamorphosing epidermal cells.

Animals↗

PubMed1975

The esterase patterns in the ovaries and the embryonated eggs of Aedes aegypti L.

The esterases of Aedes aegypti were studied in the ovary before and during a gonotrophic cycle and also in fully embryonated eggs by means of disc electrophoresis. During oogenesis no significacant changes can be observed besides a marked increase in the total esterase activity. A different esterase pattern is found in eggs after embryogenesis. The electrophoretic mobility of some esterase bands is highly increased in the ovary compared to other organs. One esterase fraction in the ovary and two in the fertilized egg were identified as acetylcholinesterases. All other enzymes are carboxylesterases. The results are compared to those of previous authors and are discussed in view of possible functions of esterases during reproduction.

Acetylcholinesterase↗