Comparing human and mouse salivary glands: A practice guide for salivary researchers

Abstract

Mice are a widely utilized in vivo model for translational salivary gland research but must be used with caution. Specifically, mouse salivary glands are similar in many ways to human salivary glands (i.e., in terms of their anatomy, histology, and physiology) and are both readily available and relatively easy and affordable to maintain. However, there are some significant differences between the two organisms, and by extension, the salivary glands derived from them must be taken into account for translational studies. The current review details pertinent similarities and differences between human and mouse salivary glands and offers practical guidelines for using both for research purposes.

Keywords: anatomy; histology; physiology; primary cells; tissue culture; tissue engineering.

Figure 1:. Anatomy of (A) human and (B) mouse salivary glands.

Both humans and mice possess three pairs of major salivary glands (the parotid, sublingual, and submandibular glands), as well as hundreds of minor salivary glands (not illustrated due to space constraints). Each major gland empties its contents into a specific duct that terminates within the oral cavity. The major salivary glands also receive blood and neuronal signals from complex networks of vessels and nerves; however, only parasympathetic innervation is depicted (again, in the interest of space). Shown are nerves (yellow), arteries and veins (red and blue respectively), ducts (green). Both frontal and side view are shown.

Figure 1:. Anatomy of (A) human and (B) mouse salivary glands.

Both humans and mice possess three pairs of major salivary glands (the parotid, sublingual, and submandibular glands), as well as hundreds of minor salivary glands (not illustrated due to space constraints). Each major gland empties its contents into a specific duct that terminates within the oral cavity. The major salivary glands also receive blood and neuronal signals from complex networks of vessels and nerves; however, only parasympathetic innervation is depicted (again, in the interest of space). Shown are nerves (yellow), arteries and veins (red and blue respectively), ducts (green). Both frontal and side view are shown.

Figure 2:. Human and mouse submandibular gland cell isolation process.

Submandibular glands (SMG) can be obtained from humans or mice, as described in Obtaining mouse and human tissue. Our lab utilizes a GentleMACS Tissue Dissociator (Miltenyi Biotec) and its associated enzyme cocktail for cell isolation, with cells later plated on ECM scaffolds to form 3D salivary spheroids (Baker, 2017).

Figure 3:. Culturing human and mouse submandibular gland cells.

Human (A-D) and mouse (E-H) SMG tissue was obtained and dissociated (as detailed in Fig. 2). Suspended cells and cell clusters were then plated on Laminin-111 (L1) gel in 8-well chambered coverglass slides and grown for 6 (A, E), 14 (B, F), and 22 (C, G) days. TO-PRO™−3 iodide and phalloidin were used to stain nuclei blue and F-actin red, respectively (A, B, C, E, F, G). Human (D) and mouse (H) SMG cells were then cultured on Laminin-111 rich gel for six days and captured in histogel for fixing, sectioning, and staining with H&E. Yellow dotted lines are indicative of lumen formation (as evidenced by a lack of nuclei) and white arrowheads point to apically localized F-actin (A, B, C, F).

Figure 4.. Markers of human and mouse salivary glands.

Submandibular glands (SMG) were frozen, fixed and stained as described in Appendix D. Then, confocal microscopy was utilized to localize some of the structural markers in native tissue from human (A, B) and mouse (C, D) SMG. White arrowheads highlight the apical localization of the tight junction protein, zonula occludens-1 (A, C; ZO-1, green) in both human (A) and mouse (C) SMG. Aquaporin-5 (B, D; AQP5, green) and cytokeratin 7 (B, D; CK7, red) identify acinar (yellow arrowheads) and ductal epithelial cells (blue arrowheads), respectively in human (B) and mouse (D) SMG.