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M Callebaut

Publications and source records attributed to M Callebaut.

At least 19 recordsLinked to original sources
PubMed2002

Avian sickle endoblast induces gastrulation or neurulation in the isolated area centralis or isolated anti-sickle region respectively.

By the quail-chicken chimera technique, we studied, in culture, the inducing effect of sickle endoblast (derived from Rauber's sickle by centripetal and cranial migration) on the isolated Rauber's sickle-free central part of the area centralis or on the isolated Rauber's sickle-free anti-sickle region from unincubated chicken blastoderms. Just as Rauber's sickle, the flat one-cell-thick sickle endoblast (Stage 2-3, Hamburger & Hamilton, 1951) induces a primitive streak (PS) and a neural plate in the area centralis. If a vitelline membrane is interposed between the sickle endoblast and the area centralis, then a small primitive streak is still induced, suggesting the effect of a diffusible factor on PS formation. In the adjacent upper layer of an isolated anti-sickle region the apposed sickle endoblast induces only a (pre)neural plate. By contrast, this (pre)neural plate inducing effect is rapidly and totally suppressed after grafting on the anti-sickle region of whole unincubated blastoderms. This suggests dominating positional information phenomena emanating from Rauber's sickle over the whole blastoderm. After grafting sickle endoblast either on the isolated area centralis or on isolated anti-sickles, no junctional endoblast and no blood islands developed. This suggests that the differentiation of Rauber's sickle material into sickle endoblast is irreversible. Our results indicate that Rauber's sickle material under the form of sickle endoblast also influences early neurulation phenomena (at distance in space and time). The present study indicates the existence of a temporo-spatially bound cascade of gastrulation and neurulation phenomena and blood island formation in the avian blastoderm, starting from Rauber's sickle, the primary major organizer with inducing, inhibiting and dominating potencies. The latter not only plays a role by secretion of signalling molecules (positional information) but it also influences development by its cell lineages (junctional endoblast and sickle endoblast).

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PubMed2002

Rauber's sickle and not the caudal marginal zone induces a primitive streak, blood vessels, blood cell formation and coelomic vesicles in avian blastoderms.

By using the quail-chicken chimera technique, we studied the reactivity and the eventual developmental or inducing capacities of the avian caudal marginal zone (in comparison with Rauber's sickle), when associated in vitro with different avian blastoderm components. If a fragment of quail sickle endoblast is placed on the caudal marginal zone of a whole unincubated chicken blastoderm, then a secondary miniature embryo will develop in this caudal marginal zone. The primitive streak and accompanying neural plate of the secondary embryo are directed peripherally into the caudal germ wall, away from Rauber's sickle. Thus, the 'mirror image development' indicates that the upper layer of the caudal marginal zone can react in the same way as the upper layer of the area centralis, because of the presence of sickle endoblast. A quail Rauber's sickle fragment placed on an isolated anti-sickle region always induces a primitive streak directed centrally. After prolonged culture, blood vessels and associated coelomic vesicles are formed. By contrast if a quail caudal marginal zone is placed on an isolated chicken anti-sickle region, the primitive streak, blood vessels and coelomic vesicles do not form. Thus, in contrast to the inducing effect of Rauber's sickle, the caudal marginal zone has no inducing effect by itself, even in the absence of the dominating effect of Rauber's sickle.

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PubMed2001

Effect of gravity on the interaction between the avian germ and neighbouring ooplasm in inverted egg yolk balls.

The developmental capacities of an avian germ (from before symmetrization to the moment of laying) are strongly diminished after inversion of its egg yolk ball followed by culture in egg white. Our present experiments show that even when the avian germ is completely horizontally inverted (without an upper or lower border) below its egg yolk ball before symmetrization, symmetrization and gastrulation phenomena take place. The germ grows slower and becomes smaller than after normal incubation. After culture of inverted unincubated germs, localized on freshly laid eggs, the closure of the neural tube is impaired and it remains open over a long distance. Although a primitive streak (PS) develops, mesoderm migration (mainly from the lateral part of the area pellucida) is also impaired. On sections through the germinal disc one can see the abnormal upward migration into the depth of the ooplasm and yolk of cells from the germ wall and the development of large cellular extensions encircling the yolk globules. Most prominent is the loss of contact between the superficial cell layers and the deep layer elements (junctional endoblast and yolk endoblast in the area opaca). Large areas without deep layer elements (even visible on surface micrographs) develop in the area vasculosa and area vitellina interna. The margin of overgrowth grows and extends normally over the egg yolk ball. An autoradiographic study after labelling of the yolk layers in inverted egg yolks reveals that mainly compression of the peripheral subgerminal and perigerminal ooplasm takes place. This suggests that the compression by the neighbouring yolk and upwards growth of cells are at the origin of the impaired development. After return to the normal upward orientation of the germ on the topmost part of the egg yolk ball, a more or less pronounced restoration to normal development takes place (depending on the duration of the inversion period and the age of the germ).

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PubMed2001

Autoradiographic evidence for the sliding of the upper layer over the basement membrane in chicken blastoderms during gastrulation.

An upper layer (epiblast) fragment taken laterally from the Anlage fields of neural plate or chordamesoderm of a quail blastoderm, labelled with 3H-glucosamine, was grafted isotopically (in a similar region), isochronically (at the similar stage of development) and isotropically (with the same caudocranial and dorsoventral polarity) in the epiblast of a mesoblast free area of a chicken blastoderm (St 4-5 Vakaet, 1970: full grown primitive streak). On the autoradiographs of the sections through such cultured blastoderms with fully integrated quail grafts, we observed a labelling of the basement membrane laterally and slightly cranially from the labelled graft in its final position. Since only the epiblast and its basement membrane are involved, the pattern of the observed labelling indicates that the grafted and integrated quail epiblast fragment glides in toto over the mediocaudally localized basement membrane, leaving behind a track of radioactivity. Sliding of whole groups of epiblast cells over the basement membrane seems thus to be a normal phenomenon during avian gastrulation.

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PubMed2000

Avian junctional endoblast has strong embryo-inducing and -dominating potencies.

In the present study, we demonstrate that quail junctional endoblast fragments have powerful embryo-inducing potencies when placed on the deep side of the upper layer (UL) of the anti-sickle region of unincubated chicken blastoderms. Moreover, in most cases the inducing potencies of the autochthonous Rauber's sickle-endophyll complex were inhibited at distance. Also, junctional endoblast still in situ in an early streak embryo strongly inhibits the inducing capacities of a Rauber's sickle - endophyll complex apposed on the deep side of the upper layer of the cranial part of the area pellucida. So junctional endoblast, besides embryo inducing potencies also seems to dominate and to inhibit at distance the gastrulation potencies of an ectopically placed or autochthonous Rauber's sickle - endophyll complex.

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PubMed1999

Endophyll orients and organizes the early head region of the avian embryo.

By placing endophyll on the caudal area marginalis situated behind Rauber's sickle of avian unincubated blastoderms, we observed after using the quail-chick chimera system and culture the development of a (pre)neural plate or a miniature embryo, head-oriented towards this endophyll. A Rauber's sickle fragment placed in the same conditions gives no reaction. If we place endophyll close to Hensen's node (stage 4 Vakaet, 1962) on an isolated anti-sickle region of an avian unincubated blastoderm in vitro, a similar endophyll-oriented development takes place after culture. Under the same conditions, but in the absence of endophyll, a Hensen's node provokes a thickening of the upper layer in the immediate neighbourhood, eventually with formation of a neural axis, oriented according to the original caudocranial direction of the graft. Our study indicates that avian endophyll (from unincubated blastoderms) can induce in the upper layer a (pre)neural plate, with or without neural folds. By interaction with sickle endoblast coming from Rauber's sickle (the early gastrulation organizer: Callebaut and Van Nueten, 1994), or from Hensen's node (a later avian organizer: Waddington, 1932), it can orient or re-orient the head region and the caudocranial direction of an induced miniature embryo. The conclusions from our embryological experiments are in agreement with the results obtained by recent molecular biology studies.

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PubMed1998

Induction of (pre) gastrulation and/or (pre) neurulation by subgerminal ooplasm and Rauber's sickle in cultured anti-sickle regions of avian unincubated blastoderms.

Rauber's sickle fragments from unincubated quail blastoderms, associated or not with chicken central subgerminal ooplasm, were placed on the deep side of the upper layer (UL) of the isolated anti-sickle region of unincubated chicken blastoderms and cultured in vitro. When only a Rauber's sickle fragment was placed, we observed always a pronounced thickening of the UL (pregastrulation) in the immediate neighbourhood. Some times a primitive streak (PS) developed. When the Rauber's sickle fragment was "sandwiched" between the UL and a central subgerminal ooplasmic mass [containing the nucleus of Pander (1817)], always a (pre)neural plate accompanied by endophyll developed, not or well associated with a primitive streak. In the latter case a complete miniature embryo developed. De novo formation of endophyll was observed. As it contained quail nuclei it was derived from Rauber's sickle cells which colonized the subgerminal ooplasm. Our experiments indicate that the uncommitted upper layer (UL) of the anti-sickle of unincubated blastoderms constitutes an excellent reactor tissue for inductions. The thickening induced in the UL of the anti-sickle region by Rauber's sickle initiates (pre)gastrulation and the thickening induced by endophyll initiates (pre)neurulation. In the beginning, pregastrulation and preneurulation seem to be independent phenomena. It is only later, when both become correctly linked at the right place and time, that a normal embryo will develop.

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PubMed1997

Avian gastrulation and neurulation are not impaired by the removal of the marginal zone at the unincubated blastoderm stage.

In the present study, we removed the whole area marginalis, Rauber's sickle and the peripheral part of the area centralis from unincubated chicken blastoderms (st IV, Vakaet, 1962a). By placing a fragment of a quail Rauber's sickle (functioning as early gastrulation organizer: Callebaut and Van Nueten, 1994) at different places and oriented in different directions on the remaining central part of the area centralis, we observed, after in vitro culture, a normal embryonic development. This indicates that the area marginalis itself is not indispensable for gastrulation and neurulation. Our study also indicates that none of the three elementary tissues (Rauber's sickle, endophyll and upper layer) of the avian unincubated blastoderm present an irreversible functional polarity.

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PubMed1996

Immunohistochemical localization of transforming growth factor-beta 1 beta 2 during folliculogenesis in the quail ovary.

Immunohistochemical methods were used to show the presence and distribution of transforming growth factor-beta 1 and beta 2 during folliculogenesis in quail ovarian tissues. The results indicated that both transforming growth factor-beta subtypes are present. Immunolabelling for transforming growth factor-beta 1 demonstrated that prelampbrush oocytes are immunoreactive in the Balbiani complex, and developing and pre-ovulatory oocytes in the zona radiata. Immunolabelling was also associated with granulosa cells. The number of stained granulosa cells decreased during folliculogenesis. In the pre-ovulatory follicles, immunolabelling was found predominantly in the theca interna. Immunolabelling for transforming growth factor-beta 2 was associated with the zona radiata of developing and pre-ovulatory follicles, and with stromal interstitial cells. Moderate immunoreactivity was found in the Balbiani complex of prelampbrush oocytes. Weak immunolabelling was localized in the granulosa cells of prelampbrush follicles, and in a few cells of the theca interna of pre-ovulatory follicles. The immunolocalization of transforming growth factor-beta 1 and -beta 2 in the quail ovary supports their autocrine and/or paracrine role in avian ovarian processes.

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PubMed1996

Map of the Anlage fields in the avian unincubated blastoderm.

By excision at different sites of rectangular fragments from unincubated chicken blastoderms and replacement by isotopic fragments from unincubated quail blastoderms, we could make the first complete map of the Anlage fields in the freshly laid avian blastoderm. All the Anlage fields (Fig. 11) are found in the upper layer (UL) of the caudal half of the area centralis (bordered by the Rauber-Koller's sickle). In the UL of the area marginalis, peripheral to Rauber-Koller's sickle, neither gastrulation nor neurulation phenomena could be observed. Similar heterotopic replacement experiments indicate that before incubation, the different parts of the UL of the area centralis are still uncommitted or reversibly committed. The Anlage fields of chordamesoblast and definitive endoderm (gut endoderm) in unincubated avian blastoderms appeared to be disposed caudally in the caudal half of the area centralis. As far as we know we are the first to demonstrate that the Anlage field of the definitive gut endoderm (which is derived from the upper layer: Hunt, 1937; Vakaet, 1962b) is localized in the most caudal upper layer part of the area centralis just centrally to the Rauber-Koller's sickle. The Anlage field of the neural plate is localized in the upper layer over the more cranial endophyll. The Anlage of the brain is shield-shaped, whilst the other Anlage fields are sickle-shaped, parallel with the Rauber-Koller's sickle. Their general hemicircular disposition and form still seem to reflect (together with the Rauber-Koller's sickle) the original ooplasmic radial symmetry (Callebaut, 1972) combined with the eccentricity of the deep layer components, which was observed during early symmetrization by gravitational orientation of the egg yolk (Callebaut, 1993a,b). The Rauber-Koller's sickle might be homologous with the vegetal dorsalizing cells or centre of Nieuwkoop (1973) in amphibian blastulas.

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PubMed1996

Localization of apoptotic cells by direct immunogold detection of digoxigenin-labeled genomic DNA in semithin sections.

In this study, which correlates apoptosis with avian ovarian physiology, we modified an in situ DNA nick end-labeling method using immunogold reagents to detect apoptotic cells in semithin sections of quail ovaries embedded in glycol methacrylate resin. Special attention was paid to the prevention of background staining. The results are comparable with those of the ApopTag peroxidase kit in paraffin-embedded ovaries.

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PubMed1995

Homology between mitochondriogenesis in the avian and amphibian oocyte.

Cytochrome oxidase cytochemistry was used to unequivocally identify the spread of mitochondria during oogenesis in the adult Japanese quail. This enabled us to compare their distribution with the distribution in the Xenopus laevis oocyte (Tourte et al, 1984). In the quail the paranuclear mitochondrial cloud initially disperses homogeneously but afterwards segregates into 2 populations: (i) a population localized in the basophilic cortical layer (surrounding the vegetal pole); and (ii) clusters of mitochondria distributed geometrically around the germinal vesicle in the animal pole. The mitochondria in these clusters have a high cytochrome oxidase activity, which reflects their functionality. This perinuclear crown of mitochondrial clusters actively replicates mtDNA in both animal species and builds up most of the stock of the mitochondria in the full-grown oocyte. Our study suggests that the perinuclear group of mitochondria will segregate in the somatic cells of the future embryo, whilst the original subcortical group will become localized in the primordial germ cells.

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PubMed1995

Gastrulation inducing potencies of endophyll and Rauber's sickle in isolated caudocranially oriented prestreak avian blastoderm quadrants (or fragments) in vitro.

Unincubated quail and prestreak chicken blastoderms were sectioned into cranial, caudal and lateral quadrants and cultured in vitro. Whilst in the caudal and lateral quadrants (containing both endophyll and Rauber's sickle material) a primitive streak (PS) developed, in the cranial quadrants (where merely central endophyll is present) only an ectoblastic thickening (early gastrula: phase I of gastrulation) appeared. If, however, sickle material was grafted on a cranial quadrant then a PS developed (phase II of gastrulation). In the anti-sickle region (lacking sickle material and endophyll) no gastrular differentiation occurred spontaneously. The grafting of endophyll and/or Rauber's sickle evokes here also phase I or II of gastrulation. When the endophyll was removed from the caudal quadrant no PS appeared. If, however, endophyll was replaced, a PS and neurula developed. Our study demonstrates that the presence of endophyll is necessary to obtain an early gastrular development (phase I of gastrulation). It seems also to have an influence on the formation of the future neurectodermal region by induction of a thickening of the cranial upper layer. Only when both endophyll and sickle material were present, a PS formed in caudal quadrants. In the caudal quadrant, the endophyll (which seems to represent the vegetative pole of the avian blastula) does not regenerate, neither from the upper layer, nor from Rauber's sickle (containing blastoporal material: Callebaut and Van Nueten: 1994).

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PubMed1995

Immunohistochemical localization of epidermal growth factor in the ovary of the adult Japanese quail.

The present study focuses on the immunohistochemical localization of epidermal growth factor in the ovary of the adult Japanese quail. Immunoreactivity was predominantly found in the smooth muscle cells of blood vessels and of chordae, in granulosa cells of pre-lampbrush follicles, in interstitial cells, in the Balbiani complex of pre-lampbrush oocytes, and in ganglia. In developing follicles, immunoreactivity was also detected in some granulosa and thecal cells, in the zona radiata, and especially in cell clusters localized in the thecal periphery. The number of immunostained cells in the granulosa decreased during folliculogenesis, and increased after ovulation. In the ooplasm of oocytes, immunoreactivity was shifted from the Balbiani complex to the zona radiata during development. These observations support the hypothesis that epidermal growth factors acts primarily on less differentiated follicles. It is also suggested that epidermal growth factor can modulate ovarian contractility. Finally, in one ovary, we detected immunostained bodies in the ooplasm of small developing oocytes.

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PubMed1995

Persistence after hypothalamectomy of a tamoxifen-like effect in the ovary of quail embryos exposed cyclically in ovo to low incubation temperatures.

Three days old quail embryos were hypothalamectomized in ovo by the decapitation technique according to Callebaut (1993). Half of these embryos was exposed to day cyclically repeated prolonged low subnormal incubation temperatures (25 degrees C). The other half of these decapitated embryos was normally continuously incubated. As is the case for not decapitated embryos the ovaries of the first group presented a tamoxifen like effect: cortical rim atrophy with proportional hypertrophy of the medulla and a pronounced decrease in the number of oogonia and oocytes. By contrast the ovaries of the second group of decapitated embryos presented a normal aspect without sterilization of the ovigerous sex cords. It was concluded that: 1. the hypophysis, the hypothalamus or other prosencephalic tissues play no intermediary role in the establishment of a tamoxifen like effect in the ovary; 2. the early embryonic development of the quail ovary during the considered period takes place without the intervention of the hypothalamus.

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PubMed1994

Rauber's (Koller's) sickle: the early gastrulation organizer of the avian blastoderm.

A fragment of Rauber's (Koller's) sickle of an unincubated quail blastoderm grafted on the ventral side of an unincubated chicken blastoderm (stage 1, Vakaet, 1962) cultured in vitro evokes the formation of a normal secundary primitive streak (PS), mesoderm and definitive (gut) endoderm, derived from the chicken host. The graft itself (containing gamma and/or beta ooplasm, Callebaut 1987) differentiates into the V-shaped junctional endoblast in continuity medially via a transitional endoblast with the median sickle endoblast (Vakaet, 1970). A PS developed also often after grafting of the caudal part of the endophyll, close to Rauber's sickle. However after grafting of the central part of the endophyll (containing delta ooplasm, Callebaut, 1987) no PS appeared. Our study indicates that material from the sickle or its derivatives represent the organizer in the early avian embryo. Comparison with the development in vivo indicated that in the avian gastrula an anchor-shaped connection area exists, situated between the sickle derived deep layer and the structures evoked in the upper layer. Our results suggest the existence of a homology between the avian Rauber's sickle and the blastoporus in amphibians and some reptiles.

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PubMed1993

In vitro study of the contractility of the wall of the preovulatory follicle in the Japanese quail.

In the present study, we examined in vitro the potassium-induced contractions of isolated parts of the wall of the quail preovulatory follicle through use of an electromagnetic force-length transducer system. We studied longitudinal and transverse strips of the whole wall, of the theca, and of the outer layer (tunica albuginea and surface epithelium). It was observed that force development and shortening of strips of the whole wall and those of the theca are similar. Statistical analysis of maximal isometric force, peak shortening length, and percentage of reduction of follicular volume showed that the orientation of strips is without importance. Results from different orientations were pooled, and the different layers were compared statistically. The general result of this analysis was that the contractile activity of the outer layer was significantly lower than the performance of either the whole wall or the theca. We concluded that contraction of the follicular wall is mainly dependent on the contractile activity of the theca externa. This contractile system is comparable to that of mammals. We suggest that the main function of the theca externa during ovulation is to maintain a constant intrafollicular pressure.

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