Number of somatic and germ cells during early stages of gonadal development in frog larvae treated with zinc sulphate.

ZnSO4 treatment of early frog tadpoles resulted, initially, in a mitotic stimulation of primordial germ cells. In later larval stages, ZnSO4 was responsible for the atresy of gonads in which germ cell and medullary cell numbers sharply decreased. At the same time, very few germ cells entered the meiotic prophase, while the degeneration of some of them was observed. Our results are discussed in connection with previous findings about the influence of Zn on cellular proliferation.

The role of the glycoconjugates in the migration of anuran amphibian germ cells.

The presence of a large amount of glycoconjugates on the anuran amphibian germ cells was demonstrated using fluorescein isothiocyanate lectins binding specifically to D-galactose and at a lower level, by other lectins binding specifically to N-acetyl-galactosamine. Glycoconjugates including D-galactose were found near the pseudopodial expansions and in the extracellular space, between germ cells and follicular cells. They were also disseminated in the cytoplasm. The injection of PNA lectin (from Arachis hypogea) into the endoderm inhibited the migration of 90% of the germ cells. This inhibition was lectin-concentration dependent. Ultrastructural study of germ cells, the migration of which was inhibited, showed that they were degenerating. These results suggest that glycoconjugates are related to the migratory activity of germ cells.

Evolution of Xenopus endodermal cells cultured on different extracellular matrix components. Identification of primordial germ cells.

Plated on untreated glass substrate, Xenopus endodermal cells are unable to undergo any morphological or cytological differentiation. Culture on artificial substrates prepared with components of the extracellular matrix, the endodermal cell behavior is entirely different. To identify the primordial germ cells (PGC), we use three coated substrate types: fibronectin, collagen and collagen plus fibronectin. These substrates allow us to distinguish three cell types shortly after explantation. Using fibronectin-coated substrate, most of the cells, after attachment and spreading, form cellular islets which tend to fuse, leading to the formation of a polyhedric cell monolayer. Such fusing is notably reduced on composite substrate (Coll + FN) or on collagen substrate only. Thus it is possible to distinguish the special morphological features exhibited by the rest of the cells. Some of them retain the aspect of endodermal gastrula cells in vitro. Others, elongated or spindle-shaped, possess the characteristics of PGC. Nevertheless, the identification and sampling of the presumed germ cells is easier on COLL + FN-coated substrate. The morphological and cytological characteristics of the elongated cells are similar to those observed during PGC migration through the endodermal mass. According to these results, there is little doubt that these elongated cells are primordial germ cells.

Freeze-fracture of Rana pipiens gonad anlage: study of primordial germ cells and other cellular types.

Freeze-fracture was used to study Anura Amphibia primordial germ cells (PGCs) from the time when they have invaded genital ridges until the time when sexual differentiation has begun. We observed tight junctions with a variety of configurations including linear, macular, and extensive occluding cross-linking complexes. True gap junctions were not observed. Rod-shaped particles were found disseminated among particles on the P fracture faces of the germ cells.

[Inhibitory effect of lectins extracted from Arachis hypogea and soybeans on germ cell migration in the embryo of Xenopus laevis (Amphibia, Anura)]. / Effet inhibiteur des lectines extraites de Arachis hypogea et du soja sur la migration des cellules germinales chez l'embryon de Xenopus laevis (Amphibien Anoure).

Effect of injection of Arachis hypogea (PNA) and Soybean (SBA) lectins on the migration of Xenopus primordial germ cells (PGCs) were investigated. PNA inhibited almost entirely the PGCs migration, more than SBA. Our results indicated that the inhibition of the migration could be a consequence of the lectin-induced alterations of cell surface properties.

Intraendodermal and intramesenteric migration of anuran amphibian germ cells: transmission and scanning electron microscopy.

Primordial germ cells (PGCs) from the dorsal side of midgut endoderm and from within the dorsal mesentery were examined by transmission and scanning electron microscopy. During migration of these cells, lamellipodia and filopodia, develop in a polarized pattern. Large amounts of extracellular material accumulate around the lamellipodia at the leading end of a migrating cell. It is suggested that the polarized pseudopodia function in conjunction with extracellular matrix as the means by which PGCs move en route to gonadal ridges.

[Detection, using fluorescent lectins, of specific carbohydrate chains in primordial germ cells of anuran amphibians]. / Détection au moyen de lectines fluorescentes de chaînes osidiques spécifiques des cellules germinales primordiales d'amphibiens anoures.

A study of primordial germ cells (PGC) of Amphibia Anura was carried out after treatment of sections by different fluorescein isothiocyanate conjugated lectins (FITC-lectins). Specific labelling on the PGC is obtained with lectins, the activity of which is inhibited by D-galactose or N-acetyl-galactosamine. These osidic groups appear to be located more specifically on the PGC. The same labelling pattern is not obtained with lectins possessing major affinity for mannose, glucose, fucose and N-acetyl-glucosamine. Furthermore, changes in labelling pattern are observed during migration of PGC. It is suggested that D-galactose and N-acetyl-galactosamine might be related to membrane activity of PGC during migration. Ultrastructural study of the visualization of cell surface carbohydrates supplies some information on the localisation of these lectins receptors.

[Ultrastructural and cytochemical characters of the primordial germ cells of the Anuran amphibians (author's transl)]. / Caractères ultrastructuraux et cytochimiques des cellules germinales primordiales des amphibiens anoures.

Transmission electron microscopy was used to study Anura Amphibia primordial germ cells (PGCs). Our results demonstrate the evidence of an extracellular matrix and many various cellular junctions between the somatic cells and the PGCs. Furthermore, from cytochemical investigation, it appears that there is abundant cytoplasmic glycogen and also membrane adenyl-cyclase activity. At last, the results are analysed, discussed and related to the hypothesis of the guidance of the migration of the Anura PGCs by cAMP diffusing from the chordo-mesoderm.

[Study of the catecholamines in the notochord of Anura Amphibia embryos. Its possible relationships with the adenyl-cyclase activity and the primordial germ cells migration (author's transl)]. / Mise en évidence de catécholamines dans la corde dorsale des embryons d'amphibiens anoures. relations possibles avec l'activité adénylate-cyclasique de cet organe et la migration des cellules germinales primordiales.

Notochord from several Anura Amphibia embryos was investigated by cytochemical study. A green fluorescence was observed, indicating a catecholamine storage in the notochord, during a precise time of their development. A stimulation of the mesoblast area by catecholamine is suggested by the analogy between the catecholamine chordal distribution and the adenyl-cyclase activity of the chordo-mesoderm. This stimulation would be followed by a cAMP production directing the PGC migration. Treatment by L-dopa increases fluorescence in the notochord. Reserpine and alpha-methyl-paratyrosine decreases the notochord fluorescence, either by stocked catecholamine depletion in the case of reserpine, or by inhibition of their synthesis by alpha-methyl-para-tyrosine.

[Cytochemical localization of an important adenyl-cyclase activity in Anuran amphibian embryo chordo-mesoderm by electron microscopy; its possible relations with the migration of primordial germ cells (author's transl)]. / Localisation cytochemique d'une importante activité adénylate cyclasique dans le cordo-mésoderme embryonnaire des amphibiens anoures. Les relations possibles avec la migration des cellules germinales primordiales.

Chordo-mesoderm of Anura Amphibia embryos was investigated by electron microscopy and a cytochemical method was used to study the localization of adenyl-cyclase activity, in this part of embryo. It seem that, in Anura, at a given stage of development, there is some adenyl-cyclase activity, and, consequently, some liberation of AMPc. Pleurodeles waltlii (Urodela Amphibia) appears to be devoid of this adenyl-cyclase activity. AMPc could be the substance provided by chordo-mesoderm attracting germinal cells.

[Influence of cyclic adenosine monophosphate on the migration of primordial germ cells of the anuran Amphibians (author's transl)]. / Influence de l'adénosine monophosphate cyclique sur la migration des cellules germinales primordiales des amphibiens anoures.

After the treatment in toto of the embryos from various species of Anura by cAMP, the number of primordial germ cells (PGC) in genital ridges is strongly reduced; the most part of the PGC are found in the endoderm. A ventral implant of agar impregnated with a solution of cAMP attracts numerous PGC in the same way as grafted chordomesoderm. The chordomesoderm itself, incubated with 3'-5' cyclic nucleotide phosphodiesterase, then grafted on to the ventral area of normal embryos attracts very few PBC compared with the non-incubated chordomesoderm. The results are analyzed and discussed along the following hypothesis: the migration of the PGC of the Anura is guided by cAMP which, diffusing from the chordomesoderm, is distributed along a concentration gradient increasing in a ventrodorsal direction. The PGC go up the gradient by a chemiotactic mechanism and reach the dorsal parts of the embryo.

[Effects of cyclic AMP treatment on the migration of primordial germ cells in the embryo of Xenopus laevis]. / Effets d'un traitement par l'AMP cyclique sur la migration des cellules germinales primordiales dans l'embryon de Xenopus laevis (amphibien anoure).

After a treatment of early embryos by AMPc, only 40% of the primordial germ cells are found in the gonads; the others are found in the dorsal mesentery and especially in the intestinal wall.

[The development of urogenital organs after lateral mesoblast heterotopic graft in the toad (Bufo bufo) neurula. II. Simultaneous inversion of anteroposterior and dorsoventral axis of the lateral plate]. / Le développement de l'appareil urogénital après la greffe hétérotopique du mésoblaste latéral chez la neurula du crapaud commun Bufo bufo L. (Amphibien anoure). II. Inversion simultanée des axes antéro-postérieur et dorso-ventral de la lame latérale.

Simultaneous inversion of the anteroposterior and dorsoventral axes of the lateral mesoblast in the early toad neurula leads to the total agenesis of the urogenital organs. The experimental results show that the lateral mesoblast is unable to undergo self-differentiation, and that three factors at least are required for the formation of the urogenital blastemata. The mesoblast must be competent: only the posterior (dorsal, but also ventral) part of the lateral mesoderm is endowed with this competence. It must receive two stimulating influences, from the cordomesoblast on the one hand, and from the dorsocaudal endoblast on the other hand.

[The development of urogenital organs after lateral mesoblast heterotopic graft in the toad (Bufo bufo) neurula. I. Distinct inversions of anteroposterior and dorsoventral axis of the lateral plate (author's transl)]. / Le développement de l'appareil uro-génital après la greffe hétérotopique du mésoblaste latéral chez la neurula du crapaud commun Bufo bufo L. (Amphibien anoure) I. Inversions separées des axes antéro-postérieur et dorso-ventral de la lame latérale.

Anteroposterior inversion of lateral mesoblast of early toad neurula is followed by differentiation of diverse urogenital blastema, according to the transplant position before the graft. Anteroposterior polarity of lateral mesoderm is thus perfectly determined in young neurula. On the contrary, dorsoventral inversion of lateral mesoblast leads to mesodermic blastema formation according to the transplant position after the graft. Particularly, the dorsal region of the lateral plates displaced to ventral position does not form blastema. On the other hand, the ventral region which shows a dorsal position after the graft develops and produces a typical blastema. Thus, in the young neurula, the dorsoventral polarity is not yet determined in the lateral plate of the mesoblast. Such a result shows also that the ventral and posterior regions of the lateral mesoblast are competent to form blastema. Moreover, factors from dorsal origin and external to lateral mesoblast take part in urogenital organ anlagen formation.

[Ultrastructural features of ureter-mesenchyme interaction, during nephrogenic induction in Amphibia]. / Aspects ultrastructuraux de l'interaction uretère-mesenchyme, au cours de l'induction néphrongène, chez les amphibiens.

Transmission electron microscopy was used to study the interface between the ureter and the mesonephric blastema. When the blastema is induced in a functional organ, numerous pseudopodial protrusions of the ureter and of the mesonephric cells lead to a close appostion between the two structures. The presence of squamous material, perhaps of a mucopolysaccharidic nature, with a network of collagen fibres is always found on this interface. These particular processes seem to play a role as a morphological basis for the phenomenon of induction. The importance of the extracellular matrix is discussed. Neither the occurrence of zones of close contact, reported by several authors, in other species, nor the fusion of membranes has ever been observed in Amphibia.

[Conseqquences of dorso-ventral and anterior-posterior reversion of early neurula lateral mesoblast on development of urogenital system in common toad, Bufo bufo. (Amphibia anura)]. / Analyse des conséquences de l'inversion dorso-ventrale et antéro-postérieure du mésoblaste latéral de la neurula sur l'édification de l'appareil uro-génital du Crapaud commun Bufo bufo L. (Amphibien Anoure)

At early neurula stage of the toad, cranio-caudal and dorso-ventral reversal of lateral mesoblast is performed. The genito-urinary system is therefore missing after this intervention. The three following factors of the formation of this system anlage are anlyzed: lateral mesoderm competence, stimulative activites of dorso-caudal endoblast on the one hand, of chordo-mesoderm on the other hand.

[The effects of anterio-posterior and dorso-ventral inversions of the lateral mesoblast of the neurula on the formation of the mesonephric, medullary, and adrenal anlage of the common toad, Bufo bufo L. (Amphibia, Anoura)]. / Conséquences de l'inversion antéropostérieure et de l'inversion dorso-ventrale du mésoblaste latéral de la neurula sur la constitution des ébauches mésonéphrogène, médullaire et interrénale du Crapaud commun, Bufo bufo L. (Amphibien Anoure)

The experimental results of cranio-caudal reversal and dorso-ventral reversal of the lateral mesoblast of the toad early neurula prove that, at this stage, the cranio-caudal polarity of this tissue is fixed but not the dorso-ventral one. External factors are responsible for the formation of mesonephric, adrenal and gonadal medullary anlage by the lateral mesoblast.

[Ultrastructure of the embryonic and larval sub-aortic blastema of Rana dalmatine (Amphibia, Anuran)]. / Observations sur l'infrastructure du blastème sous-aortique embryonnaire et larvaire de Rana dalmatina (Amphibien Anoure)

In early stages of development, the sub-aortic blastema is formed by cells of a uniform appearance filled up with lipidic inclusions. As early as stage 36, four different types of cells are present; numerous leucocytes, cells with mitochondria with tubulo-vesicular saccules, cells with granules, and cells with dense cytoplasm.