Comparative Proteomics of Mouse Tears and Saliva: Evidence from Large Protein Families for Functional Adaptation

Abstract

We produced a tear proteome of the genome mouse, C57BL/6, that contained 139 different protein identifications: 110 from a two-dimensional (2D) gel with subsequent trypsin digestion, 19 from a one-dimensional (1D) gel with subsequent trypsin digestion and ten from a 1D gel with subsequent Asp-N digestion. We compared this tear proteome with a C57BL/6 mouse saliva proteome produced previously. Sixteen of the 139 tear proteins are shared between the two proteomes, including six proteins that combat microbial growth. Among the 123 other tear proteins, were members of four large protein families that have no counterparts in humans: Androgen-binding proteins (ABPs) with different members expressed in the two proteomes, Exocrine secreted peptides (ESPs) expressed exclusively in the tear proteome, major urinary proteins (MUPs) expressed in one or both proteomes and the mouse-specific Kallikreins (subfamily b KLKs) expressed exclusively in the saliva proteome. All four families have members with suggested roles in mouse communication, which may influence some aspect of reproductive behavior. We discuss this in the context of functional adaptation involving tear and saliva proteins in the secretions of mouse lacrimal and salivary glands, respectively.

Mouse Lipocalins (MUP, OBP, LCN) Are Co-expressed in Tissues Involved in Chemical Communication

“…It is therefore likely, that LCN4 together with Vomeromodulin (Khew-Goodall et al, 1991) and MUP4 (Sharrow et al, 2002) participate in the process of pheromone access and detection by VNO. Following the process of pheromone detection, some of these proteins (LCN3, LCN4, VM, OBPs) are presumably transported to the oral cavity where they are often detected in saliva of C57BL/6 mice (Blanchard et al, 2015;Karn and Laukaitis, 2015) but, as we found in this study, their mRNAs are produced elsewhere (i.e., mainly VNO).…”

“…Similarly Obp5, Obp6, Obp7 are also highly expressed in lacrimal glands (Obp5 and Obp7 originally annotated in inbred C57BL/6 as Obp1a and Obp1b). Recently, OBP proteins have been identified in tears of the laboratory mouse C57BL/6 (Karn and Laukaitis, 2015). In this study, Obp transcripts seem to be co-expressed in combination with other lipocalins (e.g., nasal and lacrimal Obp5, Obp7, Mup4, and Lcn11).…”

“…The presence of VM (and potentially also OBP5) in the mouse saliva suggests that nasal and oral cavities are functionally connected because proteins expressed by nasal/vomeronasal tissues are also found in the oral cavity. We have also identified several proteins below 17 kDa size including PIP [Prolactin Inducible Protein-also highly abundant in saliva of the laboratory mouse (Blanchard et al, 2015)], and several unspecified members of ABP (androgen binding protein) family which were recently described in detail in the tear and saliva proteomes of the genome mouse C57BL/6 (Blanchard et al, 2015;Karn and Laukaitis, 2015).…”

“…SAL is the major salivary protein in pigs with affinity to steroids and to 2-isobutyl-3-methoxypyrazine, it is phylogenetically close to MUPs and is expressed by the male submaxillary glands (Marchese et al, 1998). Moreover, three of the six predicted OBP members described (Stopková et al, 2009(Stopková et al, , 2014 were also corroborated with MS techniques in the tear and saliva proteomes of the laboratory mouse C57BL/6 (Karn and Laukaitis, 2015), though the authors did not further specify detected OBP variants. Therefore, one of the aims of our paper was to detect potential expression sites of mRNAs coding OBPs that were found in the mouse saliva.…”

Tear Fluid Catecholamines As Biomarkers of the Parkinson’s Disease: A Clinical and Experimental Study

“…The epinephrine and dopamine levels were below the detection limit, which is most likely due to the small volume of the collected samples (1 to 2 μL). There are methods to stimulate lacrimation in animals using cholinomimetics [14], but the composition of stimulated tear fluid is known to vary significantly [15].…”