The Phenotypic Evaluation

Technician in the lab holding a mouse Ideally, three to five mice of each genotype, including the same number of age- and sex-matched controls should be submitted for evaluation. Controls should be littermates exposed to the same environment and experimental conditions, and NOT mice of the same background strain purchased from a commercial vendor. After a brief ante mortem period of observation, the mice are euthanized by carbon dioxide asphyxiation, weighed and blood collected by percutaneous cardiac puncture for subsequent hematology (complete blood count including erythrocyte, leukocyte and platelet parameters with white blood cell differential) and clinical chemistry (29 routine serum assays evaluating liver and kidney function, electrolytes and protein levels). We have a network of reference laboratories available to provide additional tests that are not performed in-house. Urine and other fluids can also be analyzed; however, due to the small volumes typically obtained from mice, pooling of samples from mice of the same genotype, age, and sex may be indicated. Digital survey radiographs, including dorsal-ventral and lateral views, are taken with the non-digital 43855A Faxitron. Digital gross photographs are taken of any lesions in mutants and their lack thereof in controls.

A complete necropsy is performed. All organs are examined grossly, and the following organs are routinely weighed to the nearest milligram prior to fixation for determining organ-to-body weight ratios (% body weight):

  • liver with gall bladder
  • spleen
  • kidneys (both)
  • adrenals (both)
  • heart
  • lungs
  • ovaries/uterus or testes/epididymides
  • thymus

Other organ(s) can be weighed based on the pathologist's recommendation and/or client's request.

Tissues are trimmed according to a standardized protocol, fixed in 10% neutral buffered formalin, processed by routine methods, embedded in paraffin wax and sectioned at 4 microns for standard H&E; unstained and frozen sections can also be made. All bony tissues are decalcified prior to trimming. The tissues noted in the table below are evaluated histologically by a comparative pathologist board-certified by the American College of Veterinary Pathologists (ACVP), frequently with the involvement of a veterinary pathology or laboratory animal trainee. Final reports include an interpretative summary and recommendations for ancillary analyses offered by the CPMPSR or other Shared Resources.

Block/Slide # Tissue
1
  • Diaphragm, semimembranosus/semitendinosus muscles
  • Sciatic nerve
2
  • Heart and aorta
  • Thymus
  • Lungs
3
  • Kidneys
4
  • Submandibular and parotid salivary glands
  • Submandibular/cervical lymph nodes
  • Mesenteric lymph nodes
5
  • Stomach, duodenum and pancreas, jejunum, ileum, cecum, colon, rectum, anus
6
  • Thyroid gland, parathyroid gland, esophagus, trachea
  • Adrenal glands
  • Ovaries
7
  • Left lateral liver lobe, median liver lobe and gall bladder
  • Spleen
8
  • Female: Uterus, cervix, vagina
  • Male: Testes and epididymides, seminal vesicles, coagulating gland, prostate gland
  • Urinary bladder
9
  • Skin from dorsum and brown adipose tissue
  • Skin from ventrum including mammary gland and clitoral/preputial gland
10
  • Femur with stifle
  • Tibia with tarsus
  • Sternum
11-12
  • Head including tongue, brain, ears, eyes, nose, teeth, pituitary
13
  • Vertebral column and spinal cord
14+
  • Lesions and/or additional sections of above tissues