DIFFERENTIATION OF KIDNEY MESENCHYME
275
microsomal antigen on the twelfth-thirteenth day of incubation (Fig. 16)
—by which time the actual age of the mesenchyme is 23-24 days. The
results were compared with observations made with fluorescent antiserum. During in vivo development, the first stained cells were seen in
15- to 16-day embryos, in which a few cells exhibited distinct fluorescence. In mesenchyme fragments cultivated in contact with the inductor, the first stained cells were discernible after 12 days cultivation
(Fig. 17).
The results show that chemodifferentiation, i.e., production of new
protein species, was not complete at the time when the developing tubules
had attained their final S-shaped form. An analogous finding has been
described by Ben-Or and Bell (1965). The induction of feathers in
chicken skin takes place between 5% and 6 days of incubation. Nevertheless, the authors could detect three new antigens immediately after
this, and yet another on the thirteenth day. Both examples show that a
new tissue component may make its appearance after a long silent
period.
C. Response at the Morphological Level
Our observations have strongly emphasized the importance of cell
surfaces and cell contacts during the aggregation of cells that marks the
beginning of the sequence of morphogenetic events, and during the subsequent development of the aggregate into a tubular structure (Saxen
and Wartiovaara, 1966; Wartiovaara, 1966b). The analysis of the
changes in the cell contacts and their correlation to other criteria of
differentiation has therefore become a pertinent matter.
The aggregation phenomenon, which follows the interaction between
the inductor tissue and the responding mesenchyme, implies changes
leading to the formation and maintenance of more or less persistent contacts between the cells involved. The theory of Steinberg (1962), developed to explain the sorting out of the cells in mixed disaggregated tissues, might also be applicable to the cellular aggregation seen in
tubulogenesis. The theory is based on the differential adhesion of randomly moving cells. Studies with time-lapse cinematography have established the randomness of the movement of the unaggregated cells in
FIG. 17. (a) The in vivo development of the kidney-specific antigen seen in
fluorographs of sections stained with antiserum conjugated to isothiocyanate. The
numbers indicate the age of the embryo, (b) Fluorograph of experimentally induced
metanephrogenic mesenchyme cultivated for 13 days. (From Lahti and Saxen, 1966.)
275
microsomal antigen on the twelfth-thirteenth day of incubation (Fig. 16)
—by which time the actual age of the mesenchyme is 23-24 days. The
results were compared with observations made with fluorescent antiserum. During in vivo development, the first stained cells were seen in
15- to 16-day embryos, in which a few cells exhibited distinct fluorescence. In mesenchyme fragments cultivated in contact with the inductor, the first stained cells were discernible after 12 days cultivation
(Fig. 17).
The results show that chemodifferentiation, i.e., production of new
protein species, was not complete at the time when the developing tubules
had attained their final S-shaped form. An analogous finding has been
described by Ben-Or and Bell (1965). The induction of feathers in
chicken skin takes place between 5% and 6 days of incubation. Nevertheless, the authors could detect three new antigens immediately after
this, and yet another on the thirteenth day. Both examples show that a
new tissue component may make its appearance after a long silent
period.
C. Response at the Morphological Level
Our observations have strongly emphasized the importance of cell
surfaces and cell contacts during the aggregation of cells that marks the
beginning of the sequence of morphogenetic events, and during the subsequent development of the aggregate into a tubular structure (Saxen
and Wartiovaara, 1966; Wartiovaara, 1966b). The analysis of the
changes in the cell contacts and their correlation to other criteria of
differentiation has therefore become a pertinent matter.
The aggregation phenomenon, which follows the interaction between
the inductor tissue and the responding mesenchyme, implies changes
leading to the formation and maintenance of more or less persistent contacts between the cells involved. The theory of Steinberg (1962), developed to explain the sorting out of the cells in mixed disaggregated tissues, might also be applicable to the cellular aggregation seen in
tubulogenesis. The theory is based on the differential adhesion of randomly moving cells. Studies with time-lapse cinematography have established the randomness of the movement of the unaggregated cells in
FIG. 17. (a) The in vivo development of the kidney-specific antigen seen in
fluorographs of sections stained with antiserum conjugated to isothiocyanate. The
numbers indicate the age of the embryo, (b) Fluorograph of experimentally induced
metanephrogenic mesenchyme cultivated for 13 days. (From Lahti and Saxen, 1966.)