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JAN 2 1965
Natl. Cancer Inst.
Monograph
MASTER
FINE STRUCTURE OF LAMPBRUSH CHROMOSOMES
conf. 234-4
0. L. MILLER, JR., Ph.D.
From the Biology Division, Oak Ridge National Laboratory,
Oak Ridge, Tennessee.
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>
LEGAL NOTICE -
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Two report me prepared uu soconut of 30monument sponsored work. Neither the Uwind
Milas, por the Commission, por nu pornou acting a bowall of the Com alaston:
A. Makut my warruat or reprodution, expressed or implied, with respect to the accr.
racy, completenee, or wafalme of the labormation contained in to report, or that the wine
of way lalormatica, appunto, machod, or procesu daclound la to report may not infringe
Minuoly one more or
1. Asmunu liabilite med respect to the wes of, or for dearu rooding from the
ure of Any laformation, menutus, method, or proces drolound la was report
As wood to the above, "person actus a bhall of the cowashao" includes may on.
Noyw or couinctor of the Countou, or aupyth of nich contractor, to the extent that
Euch anployna or contractor of the Conglasloo, or waplogue of much contructor propurus,
dornbucion, or pronto socombo, way tulonnaton pursuant to Na emplywoot or cootruct
wu the Comunalea, or to employ wat mul such contractor.

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Research sponsored by the U. S. Atomic Energy Corowad. 88100 mder contract
with the Union Carbide Corporation
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Running head;
0. L. Miller, Jr., Lampbrush Chromosomes
Send proof to:
Dr. O. L. Milier, Jr.
Biology Division
Oak Ridge National Laboratory
P. 0. Box Y
Oak Ridge, Tennessee
37831
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The lampbrush chromosomes of amphibian oocytes can readily be
18olated in a condition which closely resembles their appearance in the
living cell. These meiotic chromosomes are relatively uncoiled and in
a highly extended state when compared with chromosomes in other cell types.
In addition, labeling with radioactive precursors shows that continual,
rapid synthesis of both RNA and protein 19 occuring on these chromosome 8.
Thus, the lampbrush chromosome offers a wique opportunity for critically
examining both basic chromosome structure and structural aspects of at least
oue chromosome function - the transcription of RNA.
CURRENT CONCEPT OF STRUCTURE
..
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The summation of a number of investigations of lampbrush chromosomes
(see 1, 2 for reviews) has given rise to the concept of structure depicted
in text-figure 1 and allows the following brief description. Campbrush
chromosomes are long (up to 1 mm in length) diplotene bivalents joined by
one to several chiasnata. The main axie of each homologue contains two
chromatids and consists of a series of closely-spaced chromomeres connected
by a thin fiber. The chromatids in the main axis separate in the chromamere
regions to form the axes of pairs of lateral loops which are coated with a
ribonucleoprotein (RNP) matrix. Paired loops are similar in morphology, but
the loops mely vary in morphology from one pair to the next. Each loop 18
asymetric, having a thick and a thin end at the point of Insertion into the
main chromosome axis. The loop axes and interchromomeric threads can be
broken by DNase but not by proteases or RNase. The loop matrix material
can be removed with proteases or RNase but 18 not de formed by DNase except
through the ultimate destruction of the axis to which this material. 18
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attached.
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AL
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SAVO
PREPARATION OF LAMPBRUSH CHROMOSOMES FOR EIECTRON MICROSCOPY
Techniques for handling laupbrush chromosomes for light microscopy
have been described in detail (1, 2). The techniques pertinent to this
report involve innovations in preparing these chromosomes for electron
microscopy. Since these have not been published, they are described in
detail here. Iwo preparative procedures are used:
Surface Film Method
Wita the aid of jewelers' forceps, the nucleus of a lampbrush-stage
oocyte 18 isolated in suline and washed free of yolk with a braking, mouth
pipette. At this point, the nucleus can be treated with various agents,
changes in på or molarity, etc., which affect the structure of the chromosomes
while still in the nucleus. After the nucleus has become somewhat swollen
and turgid, it is pipetted into a small drop (2-5 mm diameter) of saline or
sucrose solution on a clean microscope slide. When sucrose is used, the
nucleus usually will rise wtil the nuclear envelope attaches to the surface
film; with saline, the drop 18 pulled down until the surface film contacts
the nucleus. In both cases, surface tension forces butst the envelope and
pull it, as well as a portion of the chromosomes and nucleoplasm into the
surface film. It is important to keep surfaces of all solutions free of oils
or other süstances which reduce surface tension or no spreading effect occurs.
After a nucleus has spread on the surface, the material in the surface film
is picked up on a carbon-coated electron microscope gria by lightly touching
the grid to the surface of the drop. The preparation then may be treated
with enzymes and stained, etc., before drying and viewing in the electron
microscope. Since soluble proteins and pazticulate materials from the
nucleoplasm, as well as sheared-off chromosomal matrix material, also are
ift
27
2
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ti
tissu
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retained on the grids by this procedure, an objectional background noise
prevents optimal viewing in preparations obtained by this method.
Hayat
Micro-centrifugation Method
three components (text-fig. 1). An upper chander (A) 18 made by attaching
a short length of glass tubing to a coverslip with epoxy resin. The middle
chamber (B) 18 constructed by glueing a funnel into a 7 to 10 mm length of
glass tubing. The funnel can be made from the highly tapered section of a
disposable Pasteur capillary pipette. The wide mouth of the funnel 18 flush
with and exactly fills the glass tubing at one end, providing a top funnel
opening of about 4 mm. The bottom end of the funnel, with an opening of
approximately 1.5 mm, should extend 1 to 1.5 mm below the end on the glass
tubing. A 2 mm-long collar of glass tubing is glued on top of the middle
chamber. The bottom chamber (c) is made by glueing to a microscope slide
a 5 to 7 roma length of a rigid, this-wall, plastic centrifuge tupe which
precisely accomodates the middle chamber. A 5 to 6 m section of rubber
tubing is slipped over the plastic section until about 1 ma of the tubing
remains above the top of the plastic chamber. The tight rubber lip acts as
a gasket and prevents liquid from being forced from the bottom chamber during
centrifugation.
The components of the centrifugation apparatus are thoroughly cleaned,
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and a washed oocyte nucleus 18 placed in the medium of choice in the upper
chamber. The chromosomes are manually isolated in the usual manner and the
dispersal of the nuclear contents followed with an inverted phase scope.
Next, the bottom chamber 18 filled with the centrifugation medium of choice
ånd an electron microscope grid (3 mm) centered in the bottom of the chamber.
The middle chamber 18 inserted into the bottom chamber until the narrow end
of the funnel 18 in contact with and centered on the grid. The level of the
centrifugation medium is adjusted watil the surface is slightly rounded above
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the top of the midate chamber.
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After the chromosomes and nucleoplasm have sufficiently spread across
the surface of the coverslip of the upper chamber, the surface of the medium
in the top chamber 18 adjusted until it is slightly rounded above the rim
of the glass tubing. The top chamber then is inverted and quickly slipped
into the top collar of the middle chamber, taking care to prevent air bubbles
from entering the apparatus. The slide holding the assembled components is
placed into a flat cardboard holder mounted on the top of a multiple centrifuge
tube carrier. The chromosomes then are centrifuged in a Size 1 Type 8B
Internation Centrifuge or equivalent for 3 to 4 minutes at a speed of 1000
to 2000 rpm. The two top chambers then are removed and the grid with attached
chromosomes treated as desired before viewing in the electron microscope.
With this method, the chromosomes can be separated from essentially all
of the background noise inherent in the surface fllm technique. In addition,
the loop matrices can either be kept intact during the procedure or partially
removed during or after centrifugatiosa
Following both methods, preparations were dehydrated in EtOH and dried
out of isopentane to minimize surface tension distortion. Most at the
observations reported here were obtained from preparations precipitated with
K-biphathalate buffer, pH4, and stained with 1-2 % VO2-acetate, på 5, for
15 to 60 minutes before dehydration.
OBSERVATIONS ON BASIC CHROMOSOME STRUCTURE
When the surface film method is used, chromosome breakage occurs during
the spreading action, preventing identification of specific chromosomes or
lateral loops. However, long portions of main chromosome axes and associated
--
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loops can be obtained on grids. (fig. 1).
In addition to breaking chromosomes,
2
UR
the surface film action removes RNP matrix material from loops, providing a
(fig. 2)
gradient ranging from loops which have retained most of their matrix to those
hearly devoid of matrix material (fig. 3). Removal of loop matrix reveals
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thet the continuity of each loop is maintained by a thin axial fiber
(= one chromatia). This fiber is broken by DNase but not by proteases or
RNase. When the matrix is cleanly removed from portions of the loop axis,
this fiber shows intermittent thick and thin regions (118. 4), with the
--
thinner regions being more prominent when severe stretching has occurred in
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the surt'ace film. Tae diameter of the thicker regions ranges from 75 to 200 X
i.
. .
.
while the thinnest regions resolved by this technique are 30 to 50 X in diameter.
.
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E
The thick portions of the axial fiber apparently consist mainly of protein
since trypsin digestion results in a general decrease in diameter and 2068 of
ZN
electron opacity after uranyl staining.
The interchromameric fiber (= two chromatids) which does not have RNP
matrix is similar in structure to the doop axes, but, on the average, is
slightly wider, ranging from 50 to 75 Å in the thin regions and up to 200 A
in diameter in the thick portions. Although The chranсmeres along the main
axi.s generally are too compact and opaque to resolve internal structure or
to observe how loop axes or interchromoneric libers are inserted. In a few
instances, however, chromomeres are found partially spread by the surface film
action and the se show a basic fibrillar lunit similar in structure and diameter.
to denuded loop axes (fig. 5).
Background noise from nucie oplasm precipitation can be eliminated in
microcentrifugation preparstions and better resolutions of axial fibers
obtained. During centrifugation, the interchramomeric fibers often are pulled
or stretched until the chronomeres become spaced some 2 to 10 microns apart
on the main chromosome axis (fig. 6). In many instances, a bead-like structure
some 500 to 700 Å in diameter 18 Pound on this fiber and usually is located
approximately midpoint between adjacent chromomeres (fig. 7). As in surface
film preparations, the interchromomeric threads, show alternating thick and
thin regions. Before protease treatment, the main axis measures some 50 to
(Pigs. 8))
150 X in diameter. After partial trypsin digestion, the thinner regions
.
.
_
A
of the main axis measure 40 to 50 Å in diameter (ligs. 10, 11) while the
thinner regions in loop axes exposed by digestion of the Loop matrix material
are 20 to 30 Å in diameter. In no case has doublene 68 of either loop axes or
main axes been observed even though the latter fiber 18 known to contain
two chromatids.
OBSERVATIONS ON THE RIBONJCIEOPROTFIN MATRIX OF LATERAL LOOPS
Three types of matrix material have been observed in centrifuged
preparations. The first type is found on a large majority of the lateral
loops and consists of clusters of ribosome-like particles interconnected by
a network of thin Bibers (fig. 12). The basic granular unit appears to be
250 to 300 Å in diameter and la favorable configurations appear to be spaced
1200 to 1500 Aapart on the fibrous componente Granules up to 800 Å in
diameter are observed in this type of matrix but these may result from
co-precipitation of two to several of the basic granular units. Estimates
ofithe number of granules in a single matrlx unit near the thick insertion
end of typical loops indicate that one matrix unit would be 5 to 8 microns
long ii the granules are attached to a single fiber.
(fig. 13)
A second type of matrix can be correlated with the fuzzy loops located
near the middle of chromosome 10 and terminal on one arm of chromosome 4 in
light microscope preparations from Triturus viridescens (1). In this type,
tre basic matrix unit is composed on long thin librils which range up to
20 microns in length when stretched in surface film preparations (fig. 15)
and up to 7 microns in centrifuged preparations (fig. 15). When these fibrils
are stretched in centrifuged preparations, they appear to have granular units
similar to those found 1005ely spaced in typical matrix units. In the fuzzy
loops, however, the particles are closely packed on a thin' axial Piber(fig. 15).
Daypsin digestion removes the granular component from loop matrices (electron
microscope observation) while RNase breaks the fibrils found on fuzzy loops

.
(phase contrast observations). These observations indicate that matrix
units are composed of a RNA PIber which either has a protein coat along
its entire length or has protein granules spaced periodically along its
length. The similarity between the granular units of both types of matrix
material may be more apparent than real, however, since typical locp matrices
precipitate between pH 3 and 5 while fuzzy loops precipitate below pH 3.
A third type of matrix, which has only occassionally been observed, appears
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same what intermediate in structure between the typical and fuzzy-type
matrices (fig. 17).
When both thin and thick insertilon ends of the same loop can be observed
(figs. 18, 19), the increase in loop diameter from the thin to the thick end
appears to be due to an increase in size of length of the matrix unit rather
than a change in overall morphology of the wit. This is especially clear in
l'uzzyLoops where the matrix fibrils show changes only in length as one travels
from the thin'to the thick insertion end. (fig. 13). In addition, there appear
to be no abrupt change in matrix unit size along the loop axis but rather a
gradual transition from a very small cluster to a large cluster on typical
loops and from a short fibril to a long fibril on fuzzy loops.
In surface film preparations in which loop matrices have been partially
removed, matrix units at the outer turn of loops often are found still attached
to the loop axis and partly to completely uncoileds and atraightened byth the
action of the Isurface film (fig. 20). Meacirements of favorable prepširations
show matrix units to range from 5 to 20 microns in length. When junctures of
matrix units and loop axes can be observed, the points of contact are marked
-
by only a slight thickening along a very short length of the loop axis. IN
preparations where matrix material has been almost completely removed from
long stretches of loop axes, granules ranging from 100 to 700 X in diameter
are found on loop axes, as well as in the background precipitation of
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10
nucleoplasm. In sorge cases, several granules may be attached to the loop
axis with a periodicity of about 1000 X (fig. 21).
DISCUSSION
In previous electron microscope studies on lampbrush chromosomes,
estimates of the diameter of the Interchromomeric fiber (two chromatids)
have ranged from 200 Å (3) to nearly 2000 Å (4) whlle the lateral loops
(one chromatia) have been considered as having a single axis between 200 and
500 X in diameter (5) or composed of a bundle of fibrils, each about 500 X
in diameter (6). The observations reported here indicate that the minimum
diameter of the loop axes is 20 to 30 Å while the interchromameric strands
measure 40 to 50 Å. These diameters are similar to those obtained by other
methods for single double-helix DNA (7) or DNP molecules (8) or for two
double-helices of DNA precipitatea together (9). These results strongly
sugeest that the chromatid, of lampbrush chromosomes consists in width of a
single DNA or DNP gmolecule. They also corroborate the conclusions drawn
by Gall (10) from the kinetics of breakage of loops and main axes of lampbrush
chromosomes by Drase, 1zez
Labeling with RNA and protein precursors show immediate incorporation
of label into both substances over the entire length of both typical and
fuzzy type loops. Gall and Callan (11), however, reported that the giant
granular loops on chromosome 12 of Triturus eristatus show sequential labeling
with time from the thin to the thick insertion ends for RNA but imediate
being synthesized at one site near the thin insertion end ther being carried
around the loop by movement of the DNA axis of the loop.
The increase in
width of the loop from the thin to the thick end was ascribed to a rotein
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synthesis.
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Recently, Gall (12) broke typical loops by X-irradiation before labeling
the RNA and found incorporation to occur on both sides of breaks. His results
indicate that RNA. synthesis occurs alsong the entire length unless one makes
the assumption that the breakage itselt initiates I new sites of RNA synthesis
on the thick insertion side of the loop. These results combined with the
observations of matrix fine structure described bere suggest that the synthesis
cf RNA molecules starts at the the thin insertion and or loops and continues
and
by a zipper-like action around then entire length of a stationary loop axis.
At any one moment, then, only a very short segment of the newly-synthesized
portion of each. RNA molecule vould be in contact with the loop axis while
the older portions of the molecules (the oldest region being at the unattdched
end) would extend into the milieu of the nucleoplasm. The similarity of
structure along the length of the RNP molecules on fuzzy-type loops and
throughout the clusters on typical loops indicates that the protein component
of loop matrices is synthesized or incorportted onto the RNA molecules at the
juncture of the loop axis and newly synthesized Iportion of the RNA molecule.
The relatively large number of matrix units per loop indicates that a
may should
correspondingly high number of RNA polymerase molecules must be present on
the loop axes. Counts of units along fuzzy loops, as well as the periodicity
of granules sometimes observed on loops stripped of matrix, suggest that the
polymerase molecules are spaced approximately 1000 Å apart along the entire
length of each loop axis.
The longest RNP un:its from fuzzy loops so far measured have been about
20 microns in length, whereas the lengths of I uzzy loops floating in solution
(i.e., unstretched) range up to 200 microns in length.
If the postulated
zipper-like synthesis of RNA molecules is correct, a comparison of the relative
lengths of loop product and loop axis indicates that the RNA polymerase
molecules may not be reading the entire length of the DNA in the loop axis,
or, alternatively, that the length of the loop axis does not consist entirely
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AC
of DNA. Since DNase digestion appears to disintegrate the entire loop
axis, the latter alternative seems less probable than the first.
als
Rough estimates of the number of RNP molecules per loop and the average
amount of RNA per unit length of DNA in loops can be made as follows. The
average length of lateral loops on lampbrush chromosomes of f. viridescens
has been reported to be 50 microns (5). The average length of matrix units
is estimated in this study to be about 10 microns and the spacing of units
..SE
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along the loop axis to be approximately 1000 Ă. Under these conditions,
the number of RNP molecules per average loop would be 500 and there would be
100 times as much RNA (on a length basis) as DNA in the lateral i dops.
One is also tempted to speculate on the significance of the length of the
RNP fibrils with respect to the function of messenger RNA. Assuming a triplet
code and an axial length of 11 Å per triplet, an RNA molecule 10 microns in
length would be sufficiently long to template code for the largest known
protein molecules (e.8., glutamic dehydrogenase, MH = LØ®ØZzzzØ 1 x 106).
In view of the fact that most proteins are considerably smaller than this
.
1
.
-
-
and that RNP molecules longer than 10 microns are present on lampbrush
-
chromosomes, it appears that fully-transcribed RNA molecules may contain more
RNA than required for their function as templates. Three explanations are
suggested: 1) The chromosomal RNA remains intact, butt the entire length of
the RNA molecule is not used during the templating process. However, estimates
of messenger length ( microns) in the largest polysomal clusters so far
$13)
observed seems to argue against this possibility; 2) Each complete molecule of
chromosomal RNA is subdivided into portions which have been transcribed by an
operator plus one or more structural genes within a single loop axis. These
Z
.
subunits of RNA would be separated during transfer to or in the cytoplasm
2
.
.
2.FP
analogous to the subdivision of ribosomal RNA reported by Perry (14); 3)
Each chromosomal RNA molecule has a common subunit which is involved in the
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movement of zessenger portions to sites of protein synthesis but which is
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detached and degraded the templating processo begins.
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3
REFERENCES
(1) GALL, J. Go: Chromosomes and cytodifferentiation. In Cytodifferentiation
and Macromolecular Synthesis (Locke, M., ed.). New York, Academic
Press Inc., 1963, pp. 119-143.
(2) CALIAN, 8. G.: The nature of lampbrush chromosomes. In International
Review of Cytology (Bourne, G. H., and Danielli, J. F., eds.). New York,
Academic Press Inc., 1963, pp. 1-34.
(2) CALIAN, 8. G., and LLOYD, L.: Lampbrush chromosomes of crested newts
Triturus cristatus (Laurenti). Phil Trans Roy Soc B 243: 135-219, 1960.
(3) TOMLIN, S. G., and CALIAN, H. G.: Preliminary account of an electron
microscope study of chromosomes from newt oocytes. Quart J Micr.Sci 92:
221-224, 1951.
(4) GUYENOT, E., and DANON, M.: Chromosomes et ovocytes des Batraciens.
Rev suisse zool 60: 1-129, 1953.
main en
(5) GALL, J. G.: On the submicroscopic structure of chromosomes. Brookhaven
Symp Biol 8: 17-32, 1956.
(6) LAFONTAINE, J. G., and RIS, .: An electron microscope study of
lampbrush chromosomes. J Biophys Biochem Cytol 4: 99-106, 1958.
(7) WILKINS, M. 8. F.: Physical studies of DNA and nucleoproteins. Sympos
Quant Biol (Cola Spring Harbor) 21: 75-88, 1956.
.
.
-
.
.
.
.
(8) ZUBAY, G., and DOTY, P.: The isolation and properties of deoxyribonucleo-
protein particles containing single nucleic acid molecules. J Molec
Biol 1: 1-20, 1959.
(9) HALL, C. E., and CAVALIERI, 1. F.: Four-stranded DNA as determined by
electron microscopy. J Biophys Biochim Cytol 10; 347-351, 1961.
...

(10) GALL, J. G.: Kinetics of de oxyribonuclease action on chromosomes.
Nature 198:36-38, 1963.
(11) GALL, J. G., and CALLAN, 8. G.: 13 uridine incorporation in lampbrush
chromosomes. Proc Nat Acad Sci USA 48: 562-570, 1962.
...
.
.
(12) GALL, J. G.: Personal communication.
(13) RICH, A., PENMAN, S., BECKER, Y., DARNELL, J., and HALL, C.:
Polyribosomes : size in normal and polio-infected He la cells.
Science 142: 1658-1663, 1963.
(14) PERRY, R. P.: Role of the nucleolus la ribonucleic acid metabolism and
other cellular processes. Nat Canc Inst Monogr 14: 73-89, 1964.
V
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16
FIGURE LEGENDS
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FIGURE 1.Portion of main axis (MA) of lampbrush chromosome with chromameres (6)
and associated lateral loops (L). Surface film. X
FIGURE 2.-Cluster of lateral loops partially stripped of RNP matrix material (M)
with exposed loop axes (IA). Surface 111m. X
FIGURE 3.-lateral doop denuded of most of RNP rastrix material exposing the
loop axis (IA). The main chromosome axis (MA) also is shown. Surface film.
S. IT
FIGURE 4.---Lateral lopp partially stripped of RNP matrix. The loop axis (IA)
shown alternating thick and thin regions along its length. Surface film. X
FIGURE 5.- Partially spread chromamere (c) and portion of loop axes (IA)
showing similar librillar structure. Surface film. X
FIGURE 6.-Main axis of lampbrush chromosome showing interchromomeric fiber (MA),
chromomeres (c), and lateral loops (L). The opaque clusters in background are
core portions of peripheral nucleoli. Micro-centrifugation. X
own.masin
in their
FIGURE 7.-Main chromosome axis showing granule (G) which occasionally observed
.
1
on the interchromomeric thread. Alternating thick and thin regions of the
i mitroller for this
thread are evident. Micro-centrifugation. X
D
FIGURE 8.--Main chromosome axis showing interchromomeric thread (MA).
Micro-centrifugation. X
mir
a
FIGURE 9.-High magnification view of interchromeric fiber shown in figure 8.
S
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-
XL
-
+
-
-
=
Minimum diameter of thread is approximately 50 A. Micro-centrifugation. X
.
1
27
FIGURE 10.-Iampbrush chromosome which has been imcompletely digested with
trypsin. Chromomeres (c), interchronomeric thread (MA), and loops (L)
-
".
-
are designated. Micro-centrifugation. X
FIGURE 11.-Hi.gh magnification view of portion of main axis shown in
figure ..0. Minimwa diameter 18 approximately 40 Å. Micro-centrlfugation.
FIGURE 12.-Lateral loops showing typical type of RNP matrix material. The
smallest, well-defined particles are 250-300 Å in diameter. Microcentrifgation.
.
...
.--
FIGURE 13.-Fuzzy type loops with well-defined microfibril as basic matrix
unit. The fibrils gradually increase in length from the thin insertion side (A)
ü to the thick insertion side (B). Microcentrifugation. X
-
-
ter
-
-
-
-
FIGURE 24.-Microfibrils (F) of fuzzy lopps uncoiled by surface film action.
Iateral loop axes are designated (L). Surface film. X
FIGURE 15.-Fuzzy loop. The extended microfibril (F) measures 4.5 microns from
loop axis to turn in fibril. The contorted fibril at the end presumably is
a shorter, unconnected piece of fibril which has been sheared off of the loop.
.
..
Micro-centrifugation. X
is
.
-
FIGURE 16.-High muignification view of portion of extended microfibril showa
in figure 15. Microcentrifugation. X .
.
-
.
.
1
.
FIGURE 17:1-Lateral loop showing a type of RNP matrix intermediate in structure
between the typical-type matrix clusters and the microfibrils on fuzzy loops.
,
Microcentrifugation. X
*
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.
.
11.
*
Whi
YL
M
11
.
16
W
FIGURE 18.-Lateral loop with typical RNP matrix showing gradual increase
in size of matrix units from the thin insertion end (A) to the thick
Insertion end (B) of the loop. Microcentrifugation. X
FIGURE 19.-Lateral loop with typical RNP matrix showing transition in
matrix size from thia (A) to thick (B) Insertipa ends Microcentrifugation.
FIGURE 20.- Iateral loop (L) with RNP matrix units uncoiled by action of
the surface film. The fibrils (F) range from 4 to 20 microns in length.
Surface film method. X
FIGURE 21.-Lateral J.oop axis (IA) stripped of matrix but showing attached
granules which occassionally have a periodicity of about 1000 Å (arrow).
Surface film. X
-.
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.
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.
.
.
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TEXT-FIG. 1
Text-figure 1.-Upper left: Diagrammatic sketch of a pair of lampbrush chremosomes
joined by two chiasmata. Upper right: Drawing of pairs of loops showing
differences in morphology and length. Bottom: Concept of continuity of
chromatids in main chromosome axis with those forming axes of the lateral
loops. (From Swanson, 1957, after Gall, 1956).
.
:
.
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