Gene Description

Symbol:  Sig

Gene:  sightless

Chromosome:  6

Allele:  Sig

Background Strain:  C57BL/6By

Strain Development:  The original mutant was the offspring of an neutron irradiated (101/Rl x C3H/Rl)F1 male. The mutation was then backcrossed onto the C57BL/6By strain by the Jackson laboratories.

Other Strain Names:  B6By.Cg-Sig/+; C57BL/6By-Sig/+; Sig mutant; Sig

Summary of Phenotype

All results must be interpreted with extreme caution as we have only examined one mutant at this time. The finding reported herein should be viewed as preliminary, observation-generating data that require confirmation before making definitive conclusions.

When observed in its home cage environment, this B6By.Cg-Sig/J mouse appears to have some visual deficits as evidenced by hyperresponsiveness to stimuli and a negative menace reflex. These findings are consistent with previous observations that these mice are "blind." At this point the only cause for vision impairment that we have identified is blepharospasm, micropalpebral fissures and entropion (examination of younger animals is necessary to make a definitive diagnosis of entropion). Entropion is a condition in which the eyelids turn in towards the eye and as a result, the eyelashes may rub against the surface of the cornea. The resulting chronic irritation can create inflammation (keratitis) and ulcers in the cornea and lead to blepharospasm. Mild medial keratitis was found in this animal, but it was not believed to be severe enough to cause visual impairment. Assessment of mice of multiple ages is warranted to further characterize this phenotype.

Summary - Gross Findings

Physical examination (including an ophthalmologic exam by a board-certified ophthalmologist) revealed nuclear cataracts in both the C57BL/6J control and B6By.Cg-Sig/J. This is not an uncommon finding in C57BL/6 mice. The B6By.Cg-Sig/J mouse had mucopurulent discharge from both eyes, small palpebral fissures, bilateral medial entropion, and keratitis of the medial aspect of corneas. No additional lesions were noted at necropsy. Eyes of the B6By.Cg-Sig/J mouse were similar in size to those of the C57BL/6J control mouse. Organ weights were similar in both mice.

Phenotypic Abnormalities - Gross Findings
B6By.Cg-Sig/J

Finding	Sex	Age	# Affected	Image(s)
Mucopurulent conjunctivitis	M	14w	1/1
Small palpebral fissures	M	14w	1/1
Bilateral medial entropion	M	14w	1/1
Keratitis	M	14w	1/1

Click on image for larger view.

Organ/Body Weights

	C57BL/6J control	B6By.Cg-Sig/J
adrenal glands (single)	0.0024g	0.0051g
body weight	29.3g	22.6g
heart	0.1792g	0.1456g
left kidney	0.2538g	0.2412g
left testicle	0.1018g	0.0965g
liver	1.1637g	1.1773g
spleen	0.0791g	0.0941g

Summary - Histology

On histologic examination, nuclear cataracts were confirmed in both mice. The B6By.Cg-Sig/J had bilateral focal medial keratitis, unilateral Harderian gland dacryoadenitis, and unilateral inflammation of the nasolacrimal ducts. There was also granulopoiesis of the spleen and bone marrow. This likely represents a response to the inflammatory processes ongoing in the ocular and periocular tissues. The other ocular tissues, including the retina were normal.

Phenotypic Abnormalities - Histology
B6By.Cg-Sig/J

Organ	Lesion	Sex	Age	# Affected	Image(s)
eye	keratitis	M	14w	1/1
Harderian gland	dacryoadenitis	M	14w	1/1
nasal cavity	inflammation of nasolacrimal duct	M	14w	1/1

Click on lesion for full description. Click on image for larger view.

Complete Data - Histology

(Click on lesion for full description.)

	C57BL/6J control	B6By.Cg-Sig/J
adrenal gland(s)
no lesions	-	-
aorta
no lesions	-	-
brown fat
no lesions	-	-
bulbourethral gland
no lesions	-	-
cecum
no lesions	-	-
cerebellum
no lesions	-	-
cerebrum
no lesions	-	-
coagulating gland
no lesions	-	-
costrochondral junction
no lesions	-	-
diaphragm
no lesions	-	-
distal colon
no lesions	-	-
duodenum
no lesions	-	-
epididymis
no lesions	-	-
exorbital gland
no lesions	-	-
eye
nuclear cataract	+	+
keratitis	-	+
femoral bone marrow
no lesions	-	-
femur
no lesions	-	-
Harderian gland
dacryoadenitis	-	+
heart
no lesions	-	-
ileum
no lesions	-	-
incisor tooth
no lesions	-	-
inner ear
no lesions	-	-
jejunum
no lesions	-	-
kidneys
no lesions	-	-
lacrimal gland(s)
no lesions	-	-
liver
microabscesses	+	+
neutrophillic infiltrates	-	+
lung
no lesions	-	-
mammary gland
no lesions	-	-
mandibular lymph node(s)
mild plasmacytosis		+
mesenteric lymph node
mild plasmacytosis		+
molar tooth
no lesions	-	-
nasal cavity
inflammation of nasolacrimal duct	-	+
granulopoiesis	-	+
pancreas
no lesions	-	-
parathyroid gland
no lesions	-	-
parotid salivary glands
no lesions	-	-
pituitary gland
no lesions	-	-
preputial glands
no lesions	-	-
prostate gland
no lesions	-	-
proximal colon
no lesions	-	-
quadriceps muscle
no lesions	-	-
sciatic nerve
no lesions	-	-
skin
no lesions	-	-
spinal cord
no lesions	-	-
spleen
granulopoiesis	-	+
stifle
no lesions	-	-
stomach
no lesions	-	-
sublingual salivary gland
no lesions	-	-
submand. salivary glands
no lesions	-	-
testes
no lesions	-	-
thymus
no lesions	-	-
thyroid gland
no lesions	-	-
tissue masses
no lesions	-	-
tongue
no lesions	-	-
trachea
no lesions	-	-
urethra
no lesions	-	-
urinary bladder
no lesions	-	-
vesicular gland
no lesions	-	-

Comments:  One tissue section of each organ or tissue was examined except for the tissues listed below:

All lung lobes were evaluated by placing the entire pluck (without the heart) into a tissue cassette.

The upper and lower gastrointestinal tracts were separated from one another and placed on the slide using the "Swiss gutroll" technique.

One eye was removed and sectioned alone, the other eye was left in the socket and was sectioned with the decalcified head.

The head was decalcified and cut into 6 sections to evaluate the sinuses, eyes, teeth, cerebrum and cerebellum.

The spinal cord was decalcified and 14-15 sections prepared.

Both gastric and splenic lobes of the pancreas were evaluated.

Both kidneys were evaluated; the left was cut longitudinally and the right was cross sectioned.

Sections were prepared from the ventromedial (including the gallbladder), left lateral and right lateral lobes of the liver.

The heart was cut into 3 cross sections to evaluate the ventricles, atria and septae.

Summary - Behavioral Testing

A series of behavioral tests were performed. The B6By.Cg-Sig/J mouse lacked a menace response (visual test) and in general was hypersensitive to physical stimuli compared to the C57BL/6J control mouse. The latter is a subjective observation and is not the result of any one specific behavioral test. The B6By.Cg-Sig/J mouse was also timid and hesitant to move into new situations or environments. We interpret this to be due to lack of or impaired sight. We also evaluated both mice in an open field activity monitoring system (see report for description and data) There were some small differences noted between the two mice including: the C57BL/6J control mouse had a higher velocity when moving, ambulated more, spent less time in a vertical position, and jumped more often than did the B6By.Cg-Sig/J. The B6By.Cg-Sig/J spent more time in the center of the testing box than did the C57BL/6J control mouse. We interpret these finding to also reflect impaired sight.

Phenotypic Abnormalities - Behavioral Testing
B6By.Cg-Sig/J

Test	Result	Sex	Age	# Affected	Image(s)
spontaneous behavior	hypersensitive	M	14w	1/1
menace relfex	negative	M	14w	1/1

Click on test for full description. Click on image for larger view.

Complete Data - Behavioral Testing

Reflex Testing

	C57BL/6J control	B6By.Cg-Sig/J
spontaneous behavior	wnl	hypersensitive
reaching reflex	wnl	wnl
trunk curl	wnl	wnl
negative geotaxis	wnl	wnl
preyer reflex	wnl	wnl
pinna reflex	wnl	wnl
vibrissae reflex	wnl	wnl

 

Open Field Locomotion

Total Activity

Open field activity assesment utilizes a a Plexiglas monitor with 289sq inches of floor space and three 16 beam arrays to measure various activity parameters when the mouse is placed in the box.

The B6By.Cg-Sig/J and C57BL/6J control mice were both placed in the activity monitor box for 60 minute testing session. The data were evaluated for the total 60 minute period (1-60) and for the last 50 minutes (11-60) of the testing session to remove the influence of the first 10 minutes of acclimation to the new environment.

	C57BL/6J control	B6By.Cg-Sig/J
Ambulatory Distance
Sum min 1-60	17,8844.14	13,108.64
Average min 1-60	2,980.74	218.48
Ambulatory Time
Sum min 1-60	814.60	674.9
Average min 1-60	13.58	11.25
Ambulatory Counts
Sum min 1-60	7164	5027
Average min 1-60	119.4	83.78
Ambulatory Episodes
Sum min 1-60	759	619
Average min 1-60	12.65	10.32
Stereotypical Time
Sum min 1-60	624.50	609.5
Average min 1-60	10.41	10.16
Stereotypical Counts
Sum min 1-60	3947	3962
Average min 1-60	65.78	66.03
Rest Time
Sum min 1-60	2080.90	2252
Average min 1-60	34.68	37.53
Vertical Counts
Sum min 1-60	942.80	1131.4
Average min 1-60	15.71	18.86
Vertical Time
Sum min 1-60	1226	1225
Average min 1-60	20.43	20.42
Clockwise Rotation
Counter Clockwise Rotation
Jump Counts
Sum min 1-60	80	63.2
Average min 1-60	1.33	1.05
Jump Time
Sum min 1-60	324	289
Average min 1-60	5.40	4.82
Average Velocity
Sum min 1-60	NA	NA
Average min 1-60	25.84	23.15
Sum min 11-60	NA

 
Total Activity Summary

The B6By.Cg-Sig/J mouse ambulated longer distances and more frequently. There were few differences in counts and time of stereotypical (repetitive) behaviors. There was little difference in vertical counts (standing on hind limbs), but the vertical time (amount of time in vertical position) was longer in the B6By.Cg-Sig/J mouse. There were small differences in clockwise and counter clockwise rotation between the two mice with both being more frequent in the C57BL/6J control mouse. The C57BL/6J control mouse had higher jump (all four feet off the ground) counts and jump times than the B6By.Cg-Sig/J. The average velocity was slightly higher in wild type mouse.

There were no differences seen between data from the total 60 minute test period (1-60) and data from the last 50 minutes (11-60) of the test period.


Zone Analysis

Open field activity data was dissected into zones within the activity monitor.

Zones 0 and 1; 0 is the periphery of the field; 1 is the center of the field.
 
Zone Analysis Summary

The C57BL/6J control mouse visited each zone more frequently than the B6By.Cg-Sig/J. The B6By.Cg-Sig/J mouse spent more time in the center zone, and the C57BL/6J control spent more time in the periphery. There were no differences seen between the data from the total 60 minutes and the data from the last 50 minutes of the test period.

Foot Print Analysis

Distance Between Stride

	C57BL/6J control	B6By.Cg-Sig/J
left forelimb 1	6.5 cm	8.5 cm
left forelimb 2	7.2 cm	8.7 cm
left forelimb 3	7.2 cm	7.3 cm
left hind limb 1	7 cm	9 cm
left hind limb 2	7 cm	8.5 cm
left hind limb 3	7 cm	6.7 cm
right forelimb 1	7.2 cm	7.8 cm
right forelimb 2	6.9 cm	8.5 cm
right forelimb 3	7.3 cm	7.8 cm
right hind limb 1	6 cm	8 cm
right hind limb 2	6.5 cm	8.5 cm
right hind limb 3	6.7 cm	7.5 cm

Widths

	C57BL/6J control	B6By.Cg-Sig/J
fore base width 1	1.9 cm	1.3 cm
fore base width 2	1.7 cm	1.5 cm
fore base width 3	1.3 cm	1.3 cm
fore/hind paw overlap 1	0.5 cm	0.7 cm
fore/hind paw overlap 2	1.1 cm	0.5 cm
fore/hind paw overlap 3	0.8 cm	0.7 cm
hind base width 1	3.2 cm	2.4 cm
hind base width 2	2.7 cm	2.5 cm
hind base width 3	3 cm	3 cm

Summary

No major deficits were noted in the B6By.Cg-Sig/J mouse.

Visual Cliff Test

The Visual cliff test evaluates vision. The mouse is placed on a Plexiglas surface in a box with a horizontal plane connected to a vertical drop, connected to another (lower) horizontal plane. A mouse with normal vision should avoid the side of the Plexiglas surface over the cliff. A mouse with impaired vision should travel over the surface of the Plexiglas with no preference for either side of the Plexiglas surface (cliff or non cliff).

Visual cliff test 1 Mice were placed on a 3 inch platform in the middle of the Plexiglas surface at the juncture between the cliff (c) and no cliff (nc) sides. The amount of time to leave the platform and side chosen (c versus nc) were recorded.

Test 1

	C57BL/6J control	B6By.Cg-Sig/J
1	nc 0s	nc 5.9s
2	c 11s	nc 62s
3	nc 18s	c 150s
4	nc 2s	c 189s
5	c 2s	nc 150s
6	nc 6s	no test>5min

Summary

Neither the C57BL/6J control nor the C57BL/6J-sig/+ mouse showed a preference for either side of the platform. The C57BL/6J-sig/+ was timid, hesitant and took longer to leave the platform than did the control mouse.

Visual cliff test 2. Mice were placed on non cliff side of platform and allowed to explore the Plexiglas surface.

Test 2

	C57BL/6J control	B6By.Cg-Sig/J
1	no pause	no pause
2	no pause	no pause

Summary

Neither mouse hesitated to cross from the non cliff to cliff side of the platform.

Visual cliff test 3. Vibrissae were removed and the mice were placed on the platform at the juncture between the cliff (c) and no cliff (nc) sides. This removed the ability of the mice to evaluate their environment using nonvisual (i.e. tactile) senses.

Test 3

	C57BL/6J control	B6By.Cg-Sig/J
1	c 9s	nc 13s
2	nc 13s	nc 88s
3	nc 17s	nc 62s
4	nc 89s	nc > 144s
5	nc 26s	no test > 4 min
6	c 41s	no test > 4 min

Summary

Neither of the mice showed a preference for cliff versus non cliff sides of the platform. The C57BL/6J-sig/+ mouse was hesitant and took longer to leave the platform.

Overall Summary / Visual Cliff: The C57BL/J control mouse did not perform in the expected manner (did not choose the non-cliff side of the apparatus). We believe that this mouse used other means to explore its environment, including vibrissae-mediated tactile senses and other visual cues. When vibrissae were removed, it is likely that the mouse had already acclimated to the apparatus and thus continued to perform in an unexpected fashion. The failure of the control mouse to perform as expected renders this test uninterpretable.

Summary - Clinical Chemistry

No genotype associated abnormalties were observed in clinical chemistry analysis.

Complete Data - Clinical Chemistry

	C57BL/6J control	B6By.Cg-Sig/J
Glucose (mg/dL)	261	198
Urea Nitrogen (mg/dL)	15	17
Creatinine (mg/dL)	0.2	0.3
Sodium (mmol/L)	144	151
Potassium (mmol/L)	4.3	3.8
Chloride (mmol/L)	112	113
Total Protein (g/dL)	4.0	5.4
Albumin (g/dL)	1.7	2.2
Globulin (g/dL)	2.3	3.2
Calcium (mg/dL)	8.9	9.6
Phosphorus (mg/dL)	9.5	9.1
Cholesterol (mg/dL)	45	112
Total Bili (mg/dL)	0.5	0.1
ALT (U/L)	69	57
ALP (U/L)	86	51
Total CO2 (mmol/L)	19	21
Anion Gap (mmol/L)	17	20

Summary - Hematology

The B6By.Cg-Sig/J had an increased white blood cell count, higher percentage of segmented neutrophils and lower percentage of lymphocytes when compared to the C57BL/6J control. The B6By.Cg-Sig/J mouse also had hypersegmented neutrophils. These findings are likely the result of the ongoing inflammation of ocular and periocular tissues.

Phenotypic Abnormalities - Hematology
B6By.Cg-Sig/J

Test	Result	Sex	Age	# Affected
Leukocytes	increased	M	14w	1/1
Neutrophils	increased	M	14w	1/1
Lymphocytes	decreased	M	14w	1/1
Lymphocyte morphology	hypersegmented neutrophils	M	14w	1/1

Complete Data - Hematology

	C57BL/6J control	B6By.Cg-Sig/J
Leukocytes
WBC (x10³/μL)	4.88	10.82
Manual differential data (smear submitted)
Segmented Neutrophils (%)	6.00	68.00
Band Neutrophils (%)	0.00	0.00
Lymphocytes (%)	88.00	28.00
Monocytes (%)	6.00	4.00
Eosinophils (%)	0.00	0.00
Basophils (%)	0.00	0.00
Nucleated RBCx (/100RBC)	0.00	0.00
Absolute leukocytes numbers calculated from manual differential
Segmented Neutrophils (x10³/μL)	0.29	7.36
Band Neutrophils (x10³/μL)	0.00	0.00
Lymphocytes (x10³/μL)	4.29	3.03
Monocytes (x10³/μL)	0.29	0.43
Eosinophils (x10³/μL)	0.00	0.00
Basophils (x10³/μL)	0.00	0.00
Differential data generated by HemaVet
Segmented Neutrophils (%)	38.89	73.86
Lymphocytes (%)	57.99	22.21
Monocytes (%)	2.44	3.14
Eosinophils (%)	0.50	0.76
Basophils (%)	0.19	0.04
Absolute leukocytes numbers calculated from HemaVet differential
Segmented Neutrophils (x10³/μL)	1.90	7.99
Lymphocytes (x10³/μL)	2.83	2.40
Monocytes (x10³/μL)	0.12	0.34
Eosinophils (x10³/μL)	0.02	0.08
Basophils (x10³/μL)	0.01	0.00
Red blood cell parameters
RBC (M/μL)	10.84	7.70
Hemoglobin (g/dL)	13.50	14.10
Hematocrit (%)	56.00	44.40
MCV (fL)	51.70	57.60
MCH (pg)	12.50	18.30
MCHC (g/dL)	24.10	31.80
Red Cell Distribution Width (%)	21.10	18.20
Platelet parameters
Platelets (x10³/μL)	625.00	763.00
MPV (fL)	4.70	5.20

Complete Urinalysis Data

	C57BL/6J control	B6By.Cg-Sig/J
glucose	-	-
pH	6.0
specific gravity	1.068
protein	++	++
blood	-
sediment exam
bilirubins	-
ketones
urobilirubins

(LEGEND:   + = positive    - = negative    ~ = suspect    QNS = quantity not sufficient    WNL = within normal limits)

Comments:  Due to small sample volume only two tests were run on urine from the Sig male and six tests on urine from the C57BL/6J control male.

Literature Review

• Searle AG
  
  Sightless, Mouse News Lett 1965;33:29



• Yen CH; Matsuda Y; Chapman VM; Elliott RW
  
  A genomic clone containing a telomere array maps near the centromere of mouse chromosome 6. Mamm Genome. 1995 Feb;6(2):96-102.



• Batchelor AL, Phillips RJ, Searle AG
  
  A comparison of the mutagenic effectiveness of chronic neutron- and gamma-irradiation of mouse spermatogonia. Mutat Res. 1966 Jun;3(3):218-29.

Availability

Available as cryopreserved line at The Jackson Laboratory.