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Biomedical subjects

D Macias

Publications and source records attributed to D Macias.

34 records · Page 2Linked to original sources
PubMed1996

Role of TGF beta s and BMPs as signals controlling the position of the digits and the areas of interdigital cell death in the developing chick limb autopod.

The establishment of the digital rays and the interdigital spaces in the developing limb autopod is accompanied by the occurrence of corresponding domains of expression of TGF beta s and BMPs. This study analyzes whether these coincident events are functionally correlated. The experiments consisted of local administration of TGF beta-1, TGF beta-2 or BMP-4 by means of heparin or Affi-gel blue beads to the chick limb autopod in the stages preceding the onset of interdigital cell death. When beads bearing either TGF beta-1 or -2 were implanted in the interdigits, the mesodermal cells were diverted from the death program forming ectopic cartilages or extra digits in a dose- and stage-dependent fashion. This change in the interdigital phenotype was preceded by a precocious ectopic expression of ck-erg gene around the bead accompanied by down-regulation of bmp-4, msx-1 and msx-2 gene expression. When BMP-beads were implanted in the interdigital spaces, programmed cell death and the freeing of the digits were both accelerated. Implantation of beads bearing BMP-4 at the tip of the growing digits was followed by digit bifurcation, accompanied by the formation of an ectopic area of cell death resembling an extra interdigit, both morphologically and molecularly. The death-inducing effect of the BMP beads and the chondrogenic-inducing effect of the TGF beta beads were antagonized by the implantation of an additional bead preabsorbed with FGF-2, which constitutes a signal characteristic of the progress zone. It is concluded that the spatial distribution of digital rays and interdigital spaces might be controlled by a patterned distribution of TGF beta s and BMPs in the mesoderm subjacent to the progress zone.

Animals↗
PubMed1995

Cell death in the embryonic developing limb.

In amniote vertebrates, the development of form and structure of the limb bud is accompanied by precise patterns of massive mesodermal cell death with morphological features of apoptosis. These areas of cell death appear to eliminate undifferentiated cells which are required only for a limited time period of limb development. Predictable skeletal and morphological anomalies of the limb occur when the pattern of cell death is modified in mutant species or under experimental conditions. Most evidence points to the occurrence of local triggering mechanisms to account for the establishment of the areas of cell death and the subsequent activation of cell death genes. Modifications of the extracellular matrix and diminution in the contribution of growth factors by neighbouring tissues appear as the most likely potential candidates for triggering the cell death program. Information on the genetical basis of cell death in the developing limb is very scarce. Among the increasing number of cell death genes identified in other cell death systems, such as p-53 and the ced-3/ICE and ced-9/ bcl-2 gene families, only bcl-2 has been studied in detail during limb development and yet, the information obtained is contradictory. Bcl-2 is not expressed in the areas of cell death of the developing limb, but normal limbs develop in mice with disruption of the bcl-2 gene. Obviously, the clarification of the role of the cell death genes constitute a major task in future studies of cell death in the developing limb.

Animals↗
PubMed1994

Pattern regulation in the chick autopodium at advanced stages of embryonic development.

In previous studies we have observed that the interdigital tissue of the chick embryo leg bud during the stages previous to interdigital cell death exhibits a considerable chondrogenic potentiality both in vivo and in vitro. In the present investigation we have carried out a variety of experimental manipulations of the chick leg bud at stage 29 to discover possible mechanisms accounting for interdigital ectopic chondrogenesis and extradigit formation. Our results show that the interdigital tissue is capable of forming an extradigit when temporarily isolated microsurgically and regrafted in its original location and after deletion of one of the adjacent digital primordia, suggesting that developing phalangeal cartilages exercise an inhibitory effect on chondrification in adjoining tissues. Furthermore, and of greater importance, ablation of the primordium of a digit is followed by normal development of the definitive digit if the wound surfaces are suitably apposed. These results reveal a considerable regulatory potential in the autopodium at advanced stages of development.

Animals↗
PubMed1994

Formation of extra digits in the interdigital spaces of the chick leg bud is not preceded by changes in the expression of the Msx and Hoxd genes.

By in situ hybridization we studied the expression patterns of Msx and Hoxd genes during the late development of the chick leg autopodium (foot) and compared them to patterns during the experimental development of interdigital extra digits. Extra digits are induced in the third interdigital space after various experimental manipulations, such as transient isolation of the interdigit, or removal of the interdigital marginal ectoderm and mesoderm. Msx1 and Msx2 are normally expressed in the interdigital tissue programmed to die. Our experiment changes the fate of the interdigital tissue from cell death to chondrogenesis and provides a good model for studying Msx involvement in defining areas of programmed cell death. Among the proposed roles of Hoxd genes is their involvement in the specification of digit identity early in development. The induction of extra digits allows us to examine whether this new morphogenetic commitment of the interdigital tissues involves changes in the domains of expression of Hoxd genes. Our results show that extra digits develop without a previous modification of the normal pattern of expression of Msx or Hoxd genes. This observation does not support the correlation between the expression of Msx genes and programmed cell death and suggests a role for these genes in maintaining the interdigital tissue in an undifferentiated state. Our results show that an increased number of digits can be formed without modifications in the pattern of expression of the 5'-located Hoxd genes and suggest the existence of latent or residual digit organization mechanisms past the time when digits are normally determined, independent of Hoxd gene expression.

Animals↗
PubMed1993

Modification of the phalangeal pattern of the digits in the chick embryo leg bud by local microinjection of RA, staurosporin and TGF beta's.

Many experimental studies show that in the avian chick limb the digits are specified at early stages of development by characteristic concentrations within the limb mesoderm of a still unidentified morphogen diffusing from the posterior margin of the bud, linked with a specific pattern of homeobox gene expression. In all these studies, digits are distinguished by their size, morphology and phalangeal pattern rather than by their position within the autopodium. In this work we report the induction of digits that have otherwise normal morphology but lack an interphalangeal joint. This suggests that the patterning of these joints is not necessarily linked to the control of the outgrowth of the digital rays. Missing interphalangeal joints were induced by microinjection into the third interdigital space of the leg bud of stage 28 to 31 chick embryos of retinoic Acid (RA), staurosporine and TGF beta 1 and beta 2, but not by microinjection of FGF or EGF. Our results also suggest that the pattern of insertion of the long tendons and the formation of the flexor cutaneous pad at the plantar surface of the digits are both linked to the establishment of the interphalangeal joints.

Alkaloids↗
PubMed1993

Internucleosomal DNA fragmentation and programmed cell death (apoptosis) in the interdigital tissue of the embryonic chick leg bud.

In this work we have attempted to characterize the programmed cell death process in the chick embryonic interdigital tissue. Interdigital cell death is a prominent phenomenon during limb development and has the role of sculpturing the digits. Morphological changes in the regressing interdigital tissue studied by light, transmission and scanning electron microscopy were correlated with the occurrence of internucleosomal DNA fragmentation, evaluated using agarose gels. Programming of the cell death process was also analyzed by testing the chondrogenic potential of the interdigital mesenchyme, in high density cultures. Our results reveal a progressive loss of the chondrogenic potential of the interdigital mesenchyme, detectable 36 hours before the onset of the degenerative process. Internucleosomal DNA fragmentation was only detected concomitant with the appearance of cells dying with the morphology of apoptosis, but unspecific DNA fragmentation was also present at the same time. This unspecific DNA fragmentation was explained by a precocious activation of the phagocytic removal of the dying cells, confirmed in the tissue sections. From our observations it is suggested that programming of cell death involves changes before endonuclease activation. Further, cell surface changes involved in the phagocytic uptake of the dying cells appear to be as precocious as endonuclease activation.

Animals↗
PubMed1993

In vivo experimental induction of interdigital tissue chondrogenesis in the avian limb bud results in the formation of extradigits. Effects of local microinjection of staurosporine, zinc chloride and growth factors.

In previous studies we had found that at late stages of development, when the early patterning control mechanism have ceased to act, the chick limb bud is able to form fully differentiated extradigits by subjecting the interdigital spaces to ectoderm removal. In this study we attempted to mimic this phenomenon by using local microinjections of substances which presumably have a biological action on the interdigital mesenchyme. Microinjection of staurosporine results in the formation of fully differentiated extradigits. The action of this drug appears to be due to the induction of chondrogenesis after the inhibition of the protein kinase C. Zinc chloride administration also causes ectopic chondrogenesis but it seems to act by arresting the interdigital cell death program through endonuclease inhibition. A clear differentiation of the zinc-induced cartilages into extradigits was no detected. This can be explained by the accompanying damage caused by zinc in the growing limb mesenchyme as deduced by the high incidence of hypophalangy in the normal digits. Both TGF beta 1 and TGF beta 2 have a weak effect as inducers of interdigital chondrogenesis; presumably they act by inducing chondrogenetic differentiation. Neither FGF nor EGF has any effect when administered by local microinjection. These results show that ectopic interdigital chondrogenesis induced by drug administration results in the differentiation of extradigits. This suggests that once a cartilage is formed in the autopodium it triggers a new signalling stage which leads to the morphogenesis of a digit. This morphogenetic process involves the patterning of skeleton, joints and tendons. In accordance with these observations, it can be proposed that early patterning of the limb results in the establishment of an autopodium with a defined but still plastic skeletal distribution pattern, while morphogenesis of each autopodial element would take place at a second stage by the activation of new signalling processes.

Alkaloids↗
PubMed1992

Interdigital chondrogenesis and extra digit formation in the duck leg bud subjected to local ectoderm removal.

In the chick embryo the interdigital tissue in the stages previous to cell death exhibits in vitro a high chondrogenic potential, and forms extra digits when subjected in vivo to local ectodermal removal. In the present work we have analyzed the chondrogenic potential both in vivo and in vitro of the interdigital mesenchyme of the duck leg bud. As distinct from the chick, the interdigital mesenchyme of the duck leg bud exhibits a low degree of degeneration, resulting in the formation of webbed digits. Our results show that duck interdigital mesenchyme exhibits also a high chondrogenic potential in vitro until the stages in which cell death starts. Once cell death is finished chondrogenesis becomes negative and the interdigital mesenchyme forms a fibroblastic tissue. In vivo the interdigital mesenchyme of the duck leg bud subjected to ectoderm removal forms ectopic foci of chondrogenesis with a range of incidence similar to that in the chick. Unlike those of the chick the ectopic cartilages of the duck are rounded and smaller, and appear to be located at the distal margin of the interdigital mesenchyme. Formation of extra digits in the duck occurs with a lower incidence than in the chick. It is concluded that ectopic chondrogenesis and formation of extra digits is related to the intensity of interdigital cell death. The non-degenerating interdigital mesenchymal cells destined to form the interdigital webs of the duck appear to contribute very little to the formation of interdigital cartilages.

Animals↗
PubMed1992

Clinically occult presentation of comminuted intertrochanteric hip fractures.

Hip fractures in awake patients are rarely subtle in their clinical presentation. We report two cases of occult, comminuted, intertrochanteric hip fractures that occurred in awake, elderly patients who were brought to the emergency department for evaluation of other medical conditions. Neither patient complained of hip pain, and both were transported to the ED without spinal immobilization. Physical examination revealed no sign of hip fracture. Patient 1 was scheduled for admission and just prior to transfer out of the ED developed hip pain. Patient 2 was admitted for workup of possible transient ischemic attack and approximately 2.5 hours after admission complained of hip pain. Radiographs of both patients revealed comminuted intertrochanteric hip fractures. In an elderly, nonambulatory patient who may have fallen prior to evaluation, routine radiographs of the pelvis and hip should be performed followed by plain tomography, computed tomography, bone scan, or magnetic resonance imaging as indicated to rule out occult hip fracture. Even comminuted intertrochanteric hip fractures can present in an occult fashion; therefore, a high index of suspicion must be maintained for these injuries.

Aged↗
PubMed1991

Structural arrangement of the extracellular matrix network during myocardial development in the chick embryo heart.

We analyzed the extracellular matrix and the connective tissue of the developing chick myocardium ("myocardial interstitium"). The importance of this myocardial element for heart function has been well documented both for the normal and pathologic adult hearts. However, little information is available on the organization of the embryonic myocardial interstitium and its modifications during development and increasing intracardiac pressure. In the present study we used light and scanning electron microscopic techniques, and lectin probes to study the interstitium of the ventricular myocardium of chick embryos from stage 29 (day 6 of development) until hatching. Our observations trace the progressive appearance and organization of the elements of the extracellular matrix, comprising the epimysium, perimysium and endomysium, which form a well-defined architectural network. Finally, we discuss the role of these elements of the extracellular matrix and their possible relation with the biomechanical properties of developing heart.

Animals↗
PubMed1990

Experimental analysis of the role of ECM in the patterning of the distal tendons of the developing limb bud.

We have shown previously that from stage 27 the distal growing region of the limb exhibits a tenascin-rich sheet of extracellular matrix termed the "mesenchyme lamina" (ML), which runs from the ectodermal basement membrane in a proximal direction until it contacts the distal tip of the muscle blocks. This study reports experimental evidence that the mesenchyme lamina is a pretendinous structure that controls the spatial organization of the flexor and extensor tendons of the distal part of the chick leg. Two sets of experiments were designed to alter the ML position and examine subsequent tendon pattern formation. In a first series of experiments limbs with digits lacking phalangeal elements were induced by AER removal at stages 26 and 27. This procedure induced an abnormal arrangement of the ML around the distal tip of each terminal phalange of the truncated digit, which was followed by the development of a precisely similar pattern of abnormal extensor and flexor tendons. In the second set of experiments, an extradigit was induced to form in the interdigital mesenchyme through surgical removal of the marginal ectoderm of the third interdigit of stage 29 leg buds. By day 4 post-operation, a chondrogenic extradigit had formed, together with a ML that ran from the cartilage to the normal ventral flexor and dorsal extensor tendons. By day 6 post-operation, the experimentally induced ML had transformed into a tendinous structure connecting with the adjacent normal tendon. Both experiments show that the position of the ML defines the position of subsequent tendon development, thus supporting its role as a pretendinous structure which might be responsible for the alignment of the pretendinous condensing cells.

Animals↗
PubMed1989

Experimental analysis of the in vivo chondrogenic potential of the interdigital mesenchyme of the chick leg bud subjected to local ectodermal removal.

Current in vitro investigations suggest that ectoderm plays a major role in limb morphogenesis by producing a diffusible factor which inhibits the chondrogenesis of the underlying mesenchyme. In the present work we report evidence supporting such an ectodermal role in vivo. Surgical removal of the marginal ectoderm from the third interdigit of chick leg buds at stages 27 to 30 induces the formation of PNA-positive prechondrogenic mesenchymal condensations 15 hr after the operation. The incidence of prechondrogenic condensations achieved 47, 95.2, and 92.8 of the experimental embryos of stages 27, 28, and 29, respectively. This high rate of prechondrogenic aggregate formation contrasted with a lower incidence of ectopic cartilage formation detectable by Alcian blue staining 40 hr after the operation. The sequential analysis of the experimental interdigits by means of peanut lectin labeling suggests that a number of prechondrogenic condensations undergo disaggregation 20 and 30 hr after the operation failing to form fully differentiated cartilages. When ectoderm removal was accompanied by the elimination of a variable amount of interdigital mesenchyme the incidence of prechondrogenic aggregates showed little differences but the formation of fully differentiated cartilages was reduced at a rate proportional to the amount of interdigital mesenchyme removed. From this study it can be concluded that the ectoderm in vivo appears to inhibit the process of aggregation of the mesenchymal cells to form prechondrogenic condensations. Furthermore our results suggest that as observed in vitro (C. P. Cotrill, C. Archer, and L. Wolpert, 1987, Dev. Biol. 122, 503-515) the transformation of prechondrogenic aggregates into fully differentiated cartilage requires the involvement of a critical amount of mesenchymal cells.

Alcian Blue↗
PubMedDate not supplied

Extracellular matrix arrangement in the papillary muscles of the adult rat heart. Alterations after doxorubicin administration and experimental hypertension.

In the present study, we analyzed the components of the extracellular matrix (ECM) and its arrangement at the level of the papillary muscles in the adult rat heart using light and transmission and scanning electron microscopy techniques. Our results reveal that after a single dose (6 mg/kg) of dexorubicin to cause a significant decrease and disorganization of the endomysium and perimysium in the first week after injection, affecting the endomysial struts and perimysial strands. Degenerating myocytes and alterations of the coiled perimysial fibers were characteristic 4 weeks after treatment. After 8 weeks, ultrastructural alterations at the level of the plasma membrane of the myocytes and adjacent collagen network were present in the tip of the papillary muscles. These alterations may be responsible for the inefficiency of the valvular apparatus as an initial factor implicated in doxorubicin-induced congestive heart failure. Experimental hypertension, produced by constriction of the abdominal aorta, induced hypertrophy of the left ventricle, with increased perimysium and endomysium of the ECM at the level of the papillary muscles 4 weeks after aortic banding. Interstitial and perivascular fibrosis were observed 8 weeks after surgical treatment, and macrophages around the degenerating myocytes were characteristic 16 weeks after treatment. These alterations of the ECM network have been correlated with their possible implication in ventricular biomechanical properties.

Animals↗
PubMedDate not supplied

Two cases of malignant lymphoma complicating autoimmune (Hashimoto's) thyroiditis.

The occurrence of lymphoma of the thyroid in a setting of autoimmune thyroid disease is being recognized with increasing frequency. The usual presentation is a rapidly enlarging goiter. This article describes two cases of this condition and emphasizes how prompt diagnosis and treatment can yield satisfactory results.

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