/. Embryo!, exp. Morph. Vol. 53, pp. 327-333, 1979
Printed in Great Britain g) Company of Biologists Limited 1979
327
Crinkly-tail, a mild skeletal mutant in the mouse
By D. R. JOHNSON 1 AND MARGARET E. WALLACE
From the Department of Anatomy, The University of Leeds
and the Department of Genetics, The University of Cambridge
SUMMARY
Crinkly-tail, cy, is a new recessive mutant with imperfect penetrance, in chromosome 4 of
the mouse. The only abnormality is in the shape of the vertebrae for one, more rarely two,
lengths of the region C9 to C14. This is expressed briefly in the 11-day-old embryo as a
duplicated tail gut. None of the mechanisms operating in most of the 20 known tail mutants
in the mouse operates in crinkly-tail. The defect is probably due to misallocation of the tissue
derived from the primitive streak.
INTRODUCTION
A mouse with a crooked tail is conspicuous amongst its fellows; for this
reason the bent mouse tail has been thoroughly researched, and most of the
mechanisms involved in its production are well understood.
When a 'new' mutant comes to light, it is necessary to approach it on two
fronts. First, it should be genetically mapped; for tail mutants this is especially
desirable because their conspicuousness makes them ideal markers. Secondly,
it should be investigated embryologically to ascertain, if possible, exactly what
has gone wrong and when.
We present here details of crinkly-tail (cy), a mutant which maps on chromosome 4, and which has small but consistent abnormalities of tail structure
apparently due to misallocation of the tissues arising from the primitive streak.
MATERIALS AND METHODS
Mice with bent or curled tails appeared in a random-bred stock known as
'Parke's albino', used in studies on reproduction. Miss Hilda Bruce held the
stock, which derived in 1922 from two pairs of mice sold by Wilson's Pet Stores,
New Oxford Street, London. She gave the aberrant mice to the second author
in 1970. This stock is thought not to be equivalent to the well-known PDE
mouse, as the eyes are pink, as in a true albino, not dark. Outcrosses to a
number of linkage marker stocks and subsequent breeding showed that a
single gene is mainly responsible, and that modifiers vary penetrance from
virtually 0 % to 100 %. Since the gene differs from any other gene affecting the
1
Author's address: Department of Anatomy, Medical and Dental Building, University of
Leeds, Leeds LS2 9JT, U.K.
328
D. R. JOHNSON AND M. E. WALLACE
Table 1. Results o/Ps/m b cy x m b cy crosses
Numbers of offspring from
Offspring
phenotypes
Female
heterozygotes
Male
heterozygotes
Ps+ + +
+ mb cy
Ps++cy
+ mb +
Ps+b cy
+ m+ +
71
67
24
14
7
5
2
128
133
53
30
8
7
1
4
1
365
Ps + b +
+ m+cy
++++
Grand totals
1
0
191
Total
199
200
77
44
15
12
3
5
1
556
tail, in either penetrance or expression, it has been given the permanent name
and symbol 'crinkly-tail, cy' (Ferguson & Wallace, 1975).
Alizarin clearance preparations were made from 16 of affected adults, and
28 embryos of different ages were examined in sections and scanning electron
micrographs.
GENETICS
Preliminary linkage data gave a gene order:
Ps-b-cy,
where Ps is polysyndactyly and b is brown (chromosome 4). Polysyndactyly
and brown have a recombination value of about 8 %, and Ps is close to misty,
m (recombination value about 1 %), with a slightly favoured order m-Ps-b
(Johnson, 1969). Linkage backcrosses Ps/m b cyxm b cy were made up; the
results from those in which c / s penetrance is 100 % are given in Table 1.
The segregation frequencies as between males and female heterozygotes are
not significantly different, although the cy recombination values are slightly
more in the male than in the female. The occurrence in the male of a single
completely normal mouse (+ + + + ) favours an order Ps-m-b; this, taken in
conjunction with Johnson's data, means there is doubt whether m is inside or
outside the segment Ps-b. There is no doubt about the order (Ps, m)-b-cy. The
cy recombination values are:
Ps-cy
Females
Males
26-18 + 3- 18
27-12 + 2- 35
m-cy
26-18±3- 18
26-85 ±2-35
b-cy
21•47 ±2-97
24•11 ±2-26
Crinkly-tail, a mild skeletal mutant in the mouse
329
Figs. 1-3. Three cy/cy mice showing various degrees of curling of the tail.
The length of the tail is not reduced. Scale bar = 1 cm.
C4
Fig. 4. Camera-lucida drawings of alizarin clearance preparations of the tails of
three cy/cy mice. In the least affected (A) two irregular vertebrae (C9 and C14 arrowed) can be seen. In the other examples the whole tail region from about C9 to
about C14 is involved.
THE ADULT
cy/cy mice have a tail defect which may range from virtual normality through
one or two slight kinks to a very deranged short region, giving the appearance
of a knot (Figs. 1-3). In alizarin clearance preparations, no abnormalities are
seen in the axial or appendicular skeleton outside the tail region. The tail has
the normal number of caudal vertebrae, there being no evidence of shortening
330
D. R. JOHNSON AND M. E. WALLACE
Fig. 5. Camera-lucida drawings of normal (A) and cy/cy (B) embryos aged 11^ days.
Note that the cy/cy tail is bent in a reversed curve and has a somewhat thickened end.
The majority of these vertebrae are indistinguishable from normal: abnormality
is seen consistently at the level of C9-C14. In mildly affected animals C9 and
C14 may be misshapen, giving two characteristic kinks to the tail. In more
severely affected tails the vertebrae between C9 and C14 are also involved,
becoming irregular and misshapen (Fig. 4).
THE EMBRYO
The first sign of abnormality detected in cy/cy embryos is at the 11-day
stage (Fig. 5) when the tail tip, instead of continuing to grow in a ventrad curve,
may turn dorsad. No sign of spina bifida or somite irregularity is visible
externally. In older embryos (13-14 days onwards) the tail is often bent through
180°, usually laterally, so that it resembles a hairpin.
In sections and scanning electron micrographs (Figs. 6, 7) the constituents of
the tail (neural tube, notochord, tail gut, vessels and somites) are usually seen
to be well-formed and in their usual positions. Near the tail tip of 11-day
embryos, however, minor irregularities can often be seen (Fig. 7), when the
tissue which is to separate into neural tube, notochord and tail gut, is misallocated. These abnormalities were seen in 19, 22 and 24 8 /mi serial sections
in the three cy/cy embryos sectioned at this age. Where such misallocations
occur, the invariable result is the formation, over a short length of tail only,
of two tail guts, one ventral and one dorsal. By the time these irregularities can
be identified externally by the presence of a curly tail (Fig. 8), the tail gut(s) have
regressed, so that, even though a single section may cut a tail transversely in
three locations, the histological appearance of each is normal.
Crinkly-tail, a mild skeletal mutant in the mouse
331
Fig. 6. Scanning electron micrograph of the broken tail of an ll-day-old cy/cy
embryo. The neural tube (NT), notochord (N), tail gut (TG) and aortae (A) are all
of normal appearance. Scale bar = 20 fim.
Fig. 7. Section taken through the distal part of an ll-day-old cy/cy embryo. The
primitive streak in this region has separated into neural tube (NT), notochord (N)
and two tail guts (TG), one dorsal to the other. Scale bar = 20 /im.
Fig. 8. Section taken through the curly part of a 13-day-old cy/cy embryo. Because
of the curl in the tail it has been cut three times in nearly transverse section. In A and
B, the more proximal sections, the tail gut has regressed; in C, closer to the tail tip
and not involved in the curl, the tail gut is present and single. Scale bar = 20 ftm.
DISCUSSION
The presence of a truncated or deformed tail in the mouse is common and has
been attributed to many causes. In Danforth's short tail (Sd, Griineberg,
1958 a), Brachyury (T, Griineberg, 1958 b), Pintail (Pt, Berry, 1960) and truncate
(tc, Theiler, 1959) the fault clearly lies in the notochord. In vestigial tail (vt,
Griineberg, 1957; Griineberg & Wickramaratne, 1974) and Bent tail (Bn,
Griineberg, 1955 a, b) the pre-axial mesoderm seems to be involved. Looptail
{Lp, Smith & Stein, 1962), curly tail (ct, Griineberg, 1954), splotch (5/7, Auerbach,
1954), crooked-tail (cd, Matter, 1957) and the Fused-kinky locus (Fu, Fuki,
332
D. R. JOHNSON AND M. E. WALLACE
Theiler & Gluecksohn-Waelsch, 1956; Gluecksohn-Schoenheimer, 1949),
undulated (un, Griineberg, 1954) and flexed tail (/, Kamenoff, 1935) seem to be
based on late-acting defects of sclerotome differentiation.
Crinkly-tail adds little to the well researched field of the bent mouse tail. We
can say that the defect is present over a short length or perhaps more commonly
over two short lengths of the otherwise normal tail, and that the only histological
abnormalities seen concern the brief presence of a duplicated tail gut. The
neural tube, as far as we can see, is normal and its closure not delayed (as in
the superficially similar ct): no spina bifida is seen in embryos and no trace of
spina bifida occulta in the adult. The notochord appears normal throughout
and no irregularities of somite formation can be seen in longitudinal sections
through the tail.
We are, therefore, forced to conclude that the rather minor phenotypic
effects of the cy gene may be based upon small errors in the allocation of tissue
amongst the derivatives of the primitive streak in the developing tail. Because
we have seen a double tail gut, we suggest that this either upsets the mechanics
of tail development so that the normal neat helical form is disturbed, or that it
serves as an indication of a malaise in the primitive streak of the tail, which leads
directly to the appearance of tail twists.
The morphology of crinkly-tail, the order (Ps, m)-b-cy and the recombination
value b-cy preclude crinkly-tail's allelism with any of the other 20 known loci
controlling tail mutants (listed, with linkages, in Mouse News Letter 59, 6-23,
1978). The nearest one chromosomally is pin-tail, Pt, which is between b and cy
and close to b; this order precludes allelism, and the aetiology is different since
pin-tail's effect arises from a fault in the development of the notochord. Only
11 of the 20 genes are mapped: this fact, and the good viability of crinkly-tail,
make it a useful addition to the list.
We are indebted to Miss J. M. Ferguson for technical assistance.
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{Received 15 March 1979, revised 21 May 1979)
EMB 53