Effects of the bovine slick mutation on heat stress responses and hair growth in mice
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The bovine slick mutations result from more than one allele variant causing a slick hair phenotype and improved thermotolerance to elevated ambient temperatures in cattle. These mutations result in the truncation of the prolactin receptor (PRLR) by 85-120 amino acids. The objective of this project was to test whether genetically modified mice with a similar truncated PRLR showed improved thermal tolerance and/or a hair phenotype. Mice were housed in environmental chambers that increased at 3[degrees]C increments every other day from 22[degrees]C until 34[degrees]C was reached. During this time feed disappearance (FD), water disappearance (WD), tail temperature (TT), and nest scores (NS) were recorded daily. Due to the association between water disappearance and feed disappearance in rodents fed pelleted diets, water disappearance per unit feed disappearance (W/F) was calculated. Female mice had a higher FD at 34[degrees]C, WD at 31[degrees]C and 34[degrees]C, and W/F ratio at 28[degrees]C, 31[degrees]C, and 34[degrees]C (P<0.05), but no differences were observed at lower temperatures (P>0.05). Genotype did not affect FD at 28[degrees]C or 31[degrees]C or W/F at 28[degrees]C, 31[degrees]C or 34[degrees]C (P>0.05). For W/F, mice heterozygous for the mutation (WT/MUT) and homozygous mutant (MUT/MUT) mice had higher ratios than homozygous wild type (WT/WT) at 22[degrees]C and 25[degrees]C (P<0.05). At 34[degrees]C there was a tendency for WT/WT to have a higher ratio than MUT/MUT. FD shows a similar trend with no differences at 28[degrees]C or 31[degrees]C. At 34[degrees]C 182 WT/WT (2.43 [plus or minus] 0.03) yielded a significantly lower FD compared to WT/MUT (2.55 [plus or minus] 0.03) and MUT/MUT (2.60 [plus or minus] 0.05) (P<0.05). At 22[degrees]C WT/WT mice (4.41 [plus or minus] 0.08) consumed a higher FD than WT/MUT (4.19 [plus or minus] 0.06) and MUT/MUT (4.13 [plus or minus] 0.12) (P<0.05). Males and females showed different TT (F= 28.84 [plus or minus] 0.0.05 vs. M= 29.07 [plus or minus] 0.06; P<0.05). WT/MUT mice had warmer TT than MUT/MUT mice (WT/MUT= 29.07 [plus or minus] 0.04 vs. MUT/MUT= 28.81 [plus or minus] 0.08; P<0.05). However, WT/MUT versus WT/WT did not differ (P>0.05). No differences existed among genotypes at each temperature for NS in females (P>0.05). Male NS did not differ at 34[degrees]C based on genotype; however, WT/MUT and MUT/MUT had higher NS than WT/WT at lower temperatures. At three weeks of age, a 1.5 cm x 1.5 cm patch was shaved on the back over the hip region on each mouse. Visual appraisals of hair regrowth were monitored daily. No difference due to genotype was observed (P<0.05); however, sex had a drastic effect on days to hair regrowth with males taking less time to show regrowth (P<0.05). In conclusion, the bovine slick mutation did appear to improve heat stress responses in mice and introduced a novel phenotype during periods of cold stress; however, since no hair phenotype was observed these effects must be acting through another mechanism, not simply due to variation in hair.
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