/. Embryo/, exp. Morph. Vol. 35, 1, pp. 197-212. 1976
Printed in Great Britain
197
Effects of formamide on
neuroepithelial cells and on interkinetic nuclear
migration in the chick embryo
By PAUL-EMIL MESSIER 1
From the De'partement cTAnatomie, Universite de Montreal
SUMMARY
Young chick embryos were incubated on media containing formamide at concentrations
of 01, 0-25, 0-31, 0-37, 0-43 and 0-5 M. In the neuroepithelium of these embryos we found that
(1) the 01 M concentration had no detectable effect, (2) the 0-25 M concentration only affected
mitosis which was blocked in metaphase so that mitotic figures accumulated near the neurocoele, (3) 0-31 M formamide totally inhibited interkinetic nuclear migration and affected
only slightly the cell asymmetry, (4) the 0-37 M concentration considerably reduced the
amount of cytoplasmic microtubules and that the cells became round, (5) at 043 M formamide,
all microtubules had disappeared and all cells were spherical, (6) at 0-5 M formamide all cells
were spherical, detached from one another and the epithelium had lost its usual characteristics.
Our results on exposure of the cells to low temperature (2 °C) suggest that formamide directly
affects microtubules. All the effects observed at concentrations up to 0-43 M formamide are
reversible.
INTRODUCTION
Neuroepithelial cells in the chick embryo are highly elongated and form a
pseudostratified columnar epithelium. Each cell has a slender cytoplasmic
process extending toward the inner surface (neurocoele) of the neural tube and
a broad portion containing the interphase nucleus found close to the basement
membrane (Fujita & Fujita, 1963; Lyser, 1964). These cells contain a large
number of microtubules aligned parallel to the cell's long axis (Messier, 1969;
Karfunkel, 1972). Interkinetic nuclear migration is known to occur in this
neuroepithelium. There is evidence suggesting a correlation between the
presence of intact microtubules and such nuclear movements (Watterson, 1965;
Pearce & Zwaan, 1970; Messier, 1972; Messier & Auclair, 1973).
During interkinetic nuclear migration, nuclei, which are situated at the base
of the cells for the majority of the cell cycle, move towards the cellular apex
where mitosis will occur. Interkinetic nuclear migration also includes the
descent of the daughter nuclei, which occurs during the Gx phase. This process
has been described in many epithelia including the nasal and lens placodes, the
1
Author's address: Departement d'Anatomie, Faculte de Medecine, Universite de
Montreal, C.P.6128, Montreal, P.Q., Canada.
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P.-E. MESSIER
mesonephrotic tubules, the thick segment of the caelum (Sauer, 1936; Sauer,
1937). It was first reported in the forming neural tube of the chick embryo by
Sauer, in 1936. Later, the concept of interkinetic nuclear migration was confirmed experimentally (Watterson, Veneziano & Bartha, 1956; Woodward &
Estes, 1944). Finally, Langman, Guerrant & Freeman (1966), in their study of
the behaviour of the neuroepithelial cells during the closure of the neural tube
have shown that during DNA synthesis (5 h) the nuclei are located at the base
of the cells near the basement membrane. Then, during the G2 phase (ca. 2-5 h),
nuclei migrate to the cell apex, near the lumen of the neural tube, to undergo
mitosis (ca. 30 min), after which they return (G l5 very short or 'non-existent')
to the outer zone of the tube to start DNA synthesis for the next division.
In the present work we use formamide which, like other amides, modifies
the conformation of protein and which biochemists use to solubilize protein
structures. This product was shown by Nevo, Mazia & Harris (1970) to disrupt
the mitotic apparatus and to alter chromosome structure in sea urchin eggs.
Their results indicated that formamide disturbed microtubular structure. These
findings prompted us to examine the action of this chemical on interkinetic
nuclear migration, a phenomenon we have shown to be related to the integrity
of microtubules in the neural tube cells of the early chick embryo (Messier &
Auclair, 1973). In this previous work we reported on a system whereby microtubules were disrupted (cold exposure) and prevented from repolymerizing
when the specimens were brought back to physiological temperature (exposure
to monoiodoacetamide, a free -SH group inhibitor). This procedure allowed us
to demonstrate that interkinetic nuclear migration was indeed inhibited in the
absence of microtubules.
We report here on the use of a much simpler approach, one which does not
interfere with -SH groups, but rather impairs normal hydrogen bonding.
MATERIALS AND METHODS
All embryos, of the chick Gallus domesticus, were explanted at 1-10 pairs of
somites (stages 7-10; Hamburger & Hamilton, 1951) and cultivated at 38 °C
for up to 6 h on Spratt's culture medium (1950). Embryos to be treated with
formamide were laid on similar media including the chemical at concentrations
of 0-1, 0-25, 0-31, 0-37, 0-43 and 0-5 M. More than 70 treated embryos were
examined; a minimum of 12 were used for each concentration except at 0-5 M
where only six were analysed. Furthermore, to test whether the effects of
formamide were reversible, eight embryos were treated with 0-37 M formamide
and six with 0-43 M for 3 h at 38 °C. They were then transferred to normal
media and incubated at 38 °C for another 3 h. Finally, to verify if formamide
could prevent the repolymerization of microtubules already disrupted by
exposure to 2 °C, nine embryos were exposed for 1-5 h at 38 °C to concentrations of formamide of 0-1 M and seven to concentration of 0-25 M. Then
Effects offormamide in the chick embryo
199
they were brought to 2 °C and kept there for 3 h after which they were
incubated, on the same media, at 38 °C for 1-5 h.
All embryos were fixed for 1 h in phosphate-buffered glutaraldehyde (1-25 %)
and post-fixed 1 h in 1 % osmium textroxide in a phosphate buffer. After dehydration in ethanol solutions, the specimens were embedded in Epon. The thin
sections, obtained with an LKB ultrotome, were stained at room temperature,
first with 1 % aqueous uranyl acetate for 20 min and with lead citrate according
to Reynolds (1963) for the same period of time. The grids were examined with
a Siemens 1A electron microscope. Sections 1 /*m thick, stained with a 1 %
aqueous solution of toluidine blue saturated with sodium borate, were used for
light microscopy.
RESULTS
Our observations deal with the effects of different concentrations of formamide as observed after a 5 h treatment (unless otherwise stated). In this report
we limit our description to (1) the shape of the neural tube, (2) the histological
aspect of the neuroepithelium,J(3) mitosis, (4) interkinetic nuclear migration
and (5) cell shape. In addition, we report on reversibility tests as well as the
effect of formamide on microtubules in particular.
0-1 M formamide
The lowest concentration of formamide used had no visible effect on any of
the five parameters mentioned above; in every respect all embryos thus treated
behaved as normal untreated specimens.
0-25 M formamide
The embryos treated at this concentration showed little growth as judged by
the segmentation of mesoderm into somites. Indeed, all experimental specimens, irrespective of their stage of development at the beginning of the treatment, gained only one pair of somites in 5 h, whereas the controls regularly
gained five in the same period of time. However, the shape of the neural tube,
as seen in transverse sections cut in front of the first pair of somites (Fig. 1),
appeared similar to that observed in normal embryos that had reached the
same stage of development (Fig. 2). This concentration then was effective in
inhibiting growth. Thus neurulation was prevented, without disturbing the
histological characteristics of the neuroepithelium.
In embryos treated with 0-25 M formamide the dividing neuroepithelial cells
were blocked in metaphase. Cross-sections of the neural tube always showed
three to four times more mitotic figures (Fig. 1) than could be counted in the
normal specimens (Fig. 2). All cells arrested in metaphase accumulated near
the neurocoele, which indicates that the interkinetic nuclear migration of the
G2-phase nuclei was not affected by this treatment. The neural tube cells in
the experimental specimens were as asymmetric as those making up the
200
P.-E. MESSIER
Effects offormamide in the chick embryo
201
neuroepithelium in the controls. Electron microscopy indicated that these cells had
as many cytoplasmic microtubules as those of normal embryos (Fig. 3). Microtubules were also observed as part of the mitotic apparatus (Fig. 4), yet it could
not be ascertained whether they were less numerous or if they were altered in
any way. The only possible discrepancy between the mitotic apparatus of these
cells as compared to controls was the occurrence of occasional thin filaments in
the vicinity of centrioles (Fig. 6).
0-31 M formamide
Following a 6 h treatment at this concentration the neural tube in most
embryos had collapsed (Fig. 5). In many instances cytoplasmic content (Fig. 7)
and even entire cells were bulging out beyond the outer edge of the neuroepithelium (Figs. 8, 9). Mitosis was still arrested in metaphase although the
mitotic figures were, in most cases, quite distorted. This was due mainly to a progressive accumulation of large inclusion droplets of varied densities near the
chromosomes (Figs. 10, 11). Furthermore, in the mitotic figures observed at
this concentration, mitochondria with ruptured cristae and concentric arrays of
endoplasmic reticulum were a constant feature (Fig. 11). Higher magnification
clearly indicated that many microtubules were present in these abnormally
dividing cells (Fig. 12).
At this concentration it was first noticed that the chemical had an inhibitory
effect on interkinetic nuclear migration. Mitotic figures were distributed
throughout the entire thickness of the neuroepithelium (Figs. 5, 8, 9). Some
mitotic figures were even seen at the base of the neuroepithelium, bulging out
beyond the outer edge of the neural tube (Fig. 9).
FIGURES
1-6
Fig. .1. Light micrograph of a section cut transversely in front of the first somite of a
10-somite embryo exposed to 025 M formamide. All features compare well with that
of a normal embryo (next figure) except that here at least eleven mitotic figures
(arrows) may be counted near the neurocoele. x 400.
Fig. 2. Light micrograph of a transverse section cut in front of the first somite of a
normal embryo with nine pairs of somites. As usual only a few mitotic figures may
be seen near the neurocoele. Arrows point to mitotic figures, x 400.
Fig. 3. Electron micrograph of portions of neuroepithelial cells from an embryo
exposed to 0-25 M formamide exhibiting abundant cytoplasmic microtubules.
x 17500.
Fig. 4. Magnification of a portion of a blocked mitosis from an embryo treated with
0-25 M formamide. On the right, part of a chromosome is seen and on the left, there
appears a centriolar structure with radiating microtubules. x 35000.
Fig. 5. Section of the neural tube of an embryo treated with 0-31 M formamide.
Note collapse of the neuroepithelium, abundant mitotic figures, especially those
situated within the thickness of the epithelium (arrows), x 400.
Fig. 6. View of a small area of the centriolar region in an embryo exposed to
0-25 M formamide. Numerous filaments (arrows) are seen, x 50000.
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P.-E. MESSIER
10
Effects offormamide in the chick embryo
203
In spite of the marked effects of the 0-31 M concentration on the shape of the
neural tube, on its histological aspect and mitosis, non-dividing cells remained
asymmetric. Yet, they definitely contained less microtubules, their mitochondria
suffered from ruptured cristae and their nucleoli, as seen in Fig. 13, were
characteristically altered.
0-37 M formamide
At a concentration of 0-37 M formamide the first important alterations in the
histological integrity of the neuroepithelium occurred. The base of the epithelial
tissue was always highly festooned and numerous cells now began to protrude
into the neurocoele (Fig. 14). The apical portions of the cells, touching upon
the neurocoele, exhibited extensive scalloping. Mitosis was rare and growth
totally inhibited. Most neuroepithelial cells had lost some of their asymmetry
yet many still contained some microtubules. These were straight though
apparently shorter than those found in normal embryos (Fig. 15).
0-43 M formamide
In all embryos treated with 0-43 M formamide the typical O shape of the
neural tube was totally obliterated (Fig. 16). The alterations in histological
integrity of the neural tube noted under the previous concentration were
accentuated at 0-43 M formamide. Most neuroepithelial cells were now definitely
spherical and devoid of microtubules.
0-5 M formamide
At this, the highest concentration we experimented with, the normal shape
and histology of the neural tube epithelium were entirely lost after the 6 h
treatment (Fig. 17). All cells were completely spherical and detached from their
neighbours (Fig. 18). Yet no pycnotic nuclei nor necrotic cells were observed
in these specimens. No traces of cytoplasmic microtubules could be found.
FIGURES
7-10
Fig. 7. Electron micrograph from a 0-31 M-treated specimen. A portion of cytoplasm
is bulging out beyond the outer edge of the neuroepithelium. Note mitochondria
with broken cristae. x 7000.
Fig. 8. Light micrograph taken from an embryo exposed to 0-31 M formamide. In
this case, the neural tube has retained its typical O shape. Extensive bulging occurs
at the base of the epithelium and many mitotic figures (arrows) are found within the
thickness of the neural tissue, x 400.
Fig. 9. Mitotic figures occupy the whole thickness of the epithelium and one is even
seen (arrow) protruding out at the base of the tissue (0-31 M formamide). x 1000.
Fig. 10. Electron micrograph of a blocked mitosis from an embryo treated with
0-31 M formamide. Large inclusion droplets are present within the chromosome
region, x 10000.
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P.-E. MESSIER
Effects offormamide in the chick embryo
205
At this concentration there appeared a peculiar and constant feature; nuclei
contained rodlets made of oriented fibrils or filaments approximately 5-7 nm
in diameter; these looked distinctly different from chromatin (Figs. 19, 20).
These filamentous intranuclear structures were generally found as a single
rodlet but occasionally they took the form of a few loosely packed bundles of
filaments intimately associated with the surrounding karyoplasm (Fig. 21).
When in the form of rodlets some were seen as small, slender, straight bodies
with blunt ends. On occasions, they were found to drastically deform the nucleus
(Fig. 20). However, none were seen to pierce the nuclear envelope and similar
filamentous structures were never noticed in the cytoplasm.
Reversibility tests
We have checked to see whether the effects of formamide, as used here, are
reversible. First, embryos ranging from one to three pairs of somites were laid
on media containing formamide at 0-37 M. Following a 3 h incubation period
they were transferred to control media for an additional 3 h. These embryos,
rather young at the beginning of the treatment, were studied macroscopically
after their 3 h stay on the normal media. Half showed signs of abnormal
morphogenesis; neurulation was inhibited and somitogenesis did not proceed
normally. Yet, on their control media mitosis resumed partially and all gained
at least two pairs of somites in a 3 h period.
Since a 0-37 M concentration only partially rids the cells of their microtubules
(see Table 1), it was decided to further test reversibility by using the next
concentration (0-43 M), which leaves the cells completely devoid of microtubules.
Here we used embryos at six pairs of somites. It was found that the collapsed
and distorted neutral tube, observed after exposure to 0-43 M formamide, is
partly reshaped following a 3 h incubation on a normal medium (Fig. 22). The
neuroepithelium resumes its normal architecture, that is, a pseudostratified
epithelium. The cytological effects with which we have been concerned are fully
reversible. Neuroepithelial cells return to their typically asymmetric shape.
Mitosis is no longer arrested, interkinetic nuclear migration occurs normally
and mitotic figures are observed only near the neurocoele (Figs. 22, 23).
Electron microscopy shows these cells contain as many microtubules as normal
embryos do (Fig. 24).
FIGURES
11—13
Fig. 11. Blocked mitosis. Note inclusion droplets of varied densities, concentric
arrays of endoplasmic reticulum and mitochondria with some missing cristae
(0-31 M formamide). x 26000.
Fig. 12. Enlarged portion of the preceding illustration showing numerous cross
sections of microtubules. Only a few are indicated by the arrows, x 44000.
Fig. 13. Altered aspect of the nucleolus as observed in neurcepithelial cells of
embryos exposed to 0-31 M formamide. x 21000.
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P.-E. MESSIER
20
Effects offormamide in the chick embryo
207
Table 1. Effects of varied concentrations of formamide on various
aspects of the chick neuroepithelium
Cone.
(M)
Arrested
mitosis
Nuclear
migration
Cell
asymmetry
Altered
neuroepithelium
Cytoplasmic
microtubules
010
—
+
0-25
+
++
0-31
++
—
0-37
++
—
N.A.
N.A.
0-43
N.A.
N.A.
0-50
A 0-25 M concentration affects only mitosis. A small increment (0-3.1 M) reduces the amount
of cytoplasmic microtubules, blocks interkinetic nuclear migration and influences cell
asymmetry. At 0-37 M only a few microtubules are observed, cell asymmetry is further
affected and signs of altered epithelium appear. Reaching 0-43 M most cells are spherical and
the pseudostratified nature of the epithelium is lost. At 0-50 M all cells are spherical. Note that
a progressive loss of cytoplasmic microtubules first affects interkinetic nuclear migration and
then leads to a gradual deterioration of cell asymmetry, N.A. stands for not applicable.
Effect offormamide on microtubules
It has been stated above that if formamide is kept at concentrations equal to
or lower than 0-25 M, it will not prevent cells from entering into mitosis and
will not disturb interkinetic nuclear migration. It is of course realized that such
concentrations, though they are relatively low compared to what is used in
biochemical practice, are definitely high from a biological standpoint and may
FIGURES
14-20
Fig. 14. Light micrograph of a section from an embryo treated with formamide at
0-37 M. Here, signs of the altered epithelial tissue are evident. Both the inner and outer
edge of the epithelium are modified. Cells no longer show their highly asymmetric
features. x400.
Fig. 15. This electron micrograph shows that some microtubules are still present in
neuroepithelial cells of embryos exposed to a 0-37 M concentration. However, in
sections, they seem shorter than those found in controls, x 40000.
Fig. 16. The typical shape of the neural tube is obliterated in this specimen treated
with 0-43 M formamide. Histological integrity is lost and cells are spherical, x 400.
Fig. 17. Low-power light micrograph of a section cut in front of an embryo with one
pair of somites exposed to 0-5 M formamide. The neuroepithelium is disintegrated.
x250.
Fig. 18. Closer view of the disintegrated neuroepithelium shown in the preceding
illustration. All cells are spherical and most are separated from each other, x 400.
Fig. 19. Part of the nucleus from a neuroepithelial cell of a specimen exposed to
a 0-5 M formamide concentration. An intranuclear rodlet of oriented filaments is
evident, x 35000.
Fig. 20. View of another rodlet, this one dramatically deforming the nucleus.
However, the nuclear membrane is still intact (arrows), x 35000.
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P.-E. MESSIER
25
Effects offormamide in the chick embryo
209
affect many cellular processes. With these points in mind it was decided to test
whether formamide could affect microtubules directly.
It is well known that temperatures of 2-4 °C have a (reversible) disrupting
effect on microtubules; this has recently been shown to apply also to the chick
embryo (Messier & Auclair, 1973; Auclair & Messier, 1974). Therefore, some
embryos explanted on 0-1 or 0-25 M formamide media were first exposed for
1-5 h at 38 °C, then to 2 °C for 3 h and finally incubated for 1-5 h at 38 °C on
their original formamide media. Using this procedure and a 0 1 M concentration, it was found that microtubules were not affected in any detectable way.
However, when 0-25 M formamide was used microtubules could no longer be
found in the neuroepithelial cells of the embryos brought back to the physiological temperature. Moreover, under these conditions, interkinetic nuclear
migration is inhibited (Fig. 25) - a stituation which is never encountered when
formamide is used alone and at concentrations not exceeding 0-25 M. Control
specimens, exposed to the cold as above and brought back to 38 °C for 1-5 h
on normal media, always contain numerous microtubules and show undisturbed
interkinetic nuclear migration. It is concluded that, in spite of its probable
effects on many cellular processes, formamide may interact with microtubular
subunits to inhibit their reassembly.
DISCUSSION
The effects of formamide on our specimens are graded. After a 6 h treatment
the chemical, at a 0-1 M concentration, had no detectable effect. A slight
increase to 0-25 M became very effective in blocking mitosis, but it did not
affect nuclear migration nor the cells' asymmetry. The accumulation of droplets
among the chromosomes might have had a cramping effect and led to mitotic
arrest. Also, although microtubules are still present in the arrested mitotic
FIGURES
21-25
Fig. 21. In some nuclei of embryos treated with 0-5 M formamide, filamentous
bodies were also seen as loosely packed bundles. Here, two such bundles are shown
at right angles, x 56000.
Fig. 22. The usually distorted neural tube observed after a 0-43 M formamide exposure regains its previous shape, following a 3 h incubation on a normal media.
In such sections mitotic figures (arrows) were seen only near the neurocoele. x 400.
Fig. 23. Higher magnification of Fig. 22. It is evident that cells have a definite
tendency to regain an asymmetric shape (compare with Fig. 16). Mitotic figures
(arrows) are found near the neurocoele. x 1000.
Fig. 24. Electron micrograph of portions of cells from an embryo exposed to
0-43 M formamide and brought back to a normal medium for 3 h. Numerous
microtubules are seen in these cells, x 35000.
Fig. 25. Section of an embryo incubated for 1-5 h at 38 °C on 0-25 M formamide,
then exposed to 2 °C for 3 h and finally incubated at 38 °C for 1-5 h. Mitotic figures
(arrows) are seen abnormally located in the thickness of the neuroepithelium. x 400.
14
EMB 35
210
P.-E. MESSIER
figures, it is possible that some were partially altered or completely disrupted
thus jeopardizing division. With an additional increment in concentration
(0-31 M), there appeared the first signs of an inhibition of interkinetic nuclear
migration. However, the molarity had to be raised to 0-37 M before the cells
began to loose some of their asymmetry. These two responses to the chemical,
(1) the increasing blockage of interkinetic nuclear migration, (2) the progressive
loss of cell asymmetry concurred, we believe, to produce the first indication of
an altered neuroepithelium. At 0-43 M formamide most cells were spherical
and devoid of microtubules whereas at 0-5 M all cells were completely spherical.
However, this last concentration did not produce pycnotic nuclei nor necrosis
after a 6 h exposure, an indication that the cells manage to resist the toxicity
of the product.
The results obtained by coupling exposure to low temperature and a low
concentration of formamide support the idea that the chemical, although it
probably affects many cellular processes, does interact directly with the components of depolymerized microtubules. It is thought that increasing concentrations of formamide could gradually disturb the polymerization of microtubular components therefore gradually affecting more and more microtubules.
At a concentration of 0-25 M formamide acts only as a mitotic inhibitor whereas
at 0-31 M formamide affects microtubules to the extent of blocking nuclear
migration of nuclei in their G2 phase. Then the chemical at a concentration of
0-37 M reaches most microtubules and finally all of them (0-43 M) as may be
followed by the stepwise loss of cell asymmetry.
At a 0-5 M concentration one additional anomaly arises. Rodlets of oriented
fibrils are found in the nuclei of the neuroepithelial cells and in nuclei of the
other embryonic leaflets. The occurrence of such bands or rodlets of intranuclear
filaments has been observed for over 80 years under both normal and pathological conditions (see Clattenburg, Singh & Montemurro, 1972); yet their
genesis, chemical nature and functional significance are not well understood.
Their nature and origin in our material are presently being investigated.
Our reversibility tests clearly show that the cytological effects with which we
are concerned are fully reversible. The reversibility of the inhibition of interkinetic nuclear migration indicates that the chemical did not interfere with the
process of differentiation but suppressed the manifestation of differentiated
functions.
In 1966, Waddington & Perry suggested that microtubules might play a role
in the cell deformations that ensure neurulation in amphibians. As it was
stated then microtubules appeared as shape-generating structures that mainly
induce cell elongation. Since then many reports, covering an impressive variety
of cell systems, have shown the existence of a correlation between the presence
of microtubules and the production and/or maintenance of cell asymmetry.
Such a correlation has been established in the cells of the neuroepithelium of
the chick embryo (Auclair & Messier, 1974).
Effects offormamide in the chick embryo
211
Elongation, however, is not the only alteration of cell shape that ensures
neurulation. Indeed cells elongate; this has been termed the acquisition of
asymmetry. However, cells also acquire a slender apical region and a broad
basal portion, which we shall call dissymmetry. The origin of this apico-basal
dissymmetry has been attributed to the constriction of apically situated microfilaments (Baker & Schroeder, 1967; Karfunkel, 1972). Whether these microfilaments contract or not, the possibility still exists that forces within the cytoplasm underneath this filamentous collar will determine the extent of the cell's
width in its basal position. The nucleus, which rests at the base of the cell for
the longest part of the cell cycle (Langman et ah 1966), may be involved in the
production of the apico-basal dissymmetry. Accordingly the forces moving
the nucleus should be considered as an important factor in the induction of the
dissymmetry. We provide here experimental data suggesting that microtubules
are part of the active forces involved in the displacement of nuclei observed
during interkinetic nuclear migration.
It should be emphasized that microtubules might not be the only agent
involved in nuclear migration. Indeed we recently showed that cytochalasin B
is also capable of blocking interkinetic nuclear migration (Messier & Auclair,
1974) and determined that microtubules are not structurally affected by the
drug (Messier & Auclair, 1975).
In conclusion, it seems that microtubules not only participate in maintaining
the elongation of cells but also, through their role in interkinetic nuclear
migration, are involved in the production of apico-basal dissymmetries that
favour the invagination of the neuroepithelium, a prerequisite for neurulation.
RESUME
Effets de la formamide sur les cellules neuroepitheliales et la migration nucleaire inter cinetique
chez Vembryon de poulet
De jeunes embryons de poulet ont ete incubes sur des milieux de culture enrichis de
formamide aux concentrations de 0 1 , 0-25, 0-31, 0-37, 0-43 et 0-5 M. Dans leur neuroepithelium, nous observons que (1) la concentration de 01 M n'a aucun effet decelable,
(2) la concentration de 0-25 M n'agit que sur les mitoses qui toutes sont bloquees en metaphase
a l'apex des cellules neuroepitheliales, (3) a 0-31 M la formamide inhibe totalement la migration nucleaire intercinetique, n'affectant que tr6s peu l'asymetrie cellulaire, (4) la concentration de 0-37 M reduit considerablement le nombre des microtubules cytoplasmiques et induit
l'arrondissement de la majorite des cellules, (5) a 0-43 M, tous les microtubules sont disparus
et toutes les cellules sont rondes, (6) a 0-5 M, toutes les cellules sont rondes, detachees les
unes des autres et le neuroepithelium a complement perdu ses caract&res histologiques
habituels. De plus, des traitements au froid permirent de montrer que la formamide agissait
directement sur les microtubules. Tous les effets produits par la formamide, jusqu'a la
concentration de 0-43 M, sont reversibles.
We are grateful to Madame Genevieve Anglade and M. Jean Leveille for their technical
assistance, to Mile M. Adolphe for her secretarial work and to Miss H. Stephens for her aid
with the English translation. This work was supported by the Medical Research Council of
Canada and by the Health and Welfare Department, RODA section.
14-2
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P.-E. MESSIER
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AUCLAIR,
{Received 16 July 1975)