The class B, type I scavenger receptor (Srb1 or Scarb1) is a cell surface HDL receptor that can recognize the apolipoproteins on the surface of the HDL particle. It plays a key role in determining the levels of plasma lipoprotein cholesterol (primarily HDL) and the accumulation of cholesterol stores in the adrenal gland.In this strain plasma cholesterol (primarily HDL) concentrations increase by 125% in homozygotes and 31% in heterozygotes, as compared to wild type controls. Also, cholesterol levels in adrenal tissue in homozygous and heterozygous mutants decrease by 72% and 42% respectively, relative to wild type controls. The plasma concentration of Apoa-I, the major protein in HDL, is unchanged in mutant animals, relative to wild type controls.
 On a mixed genetic background (B6;129), homozygous females are infertile and homozygous males are fertile. As of 2008, the donating investigator reported that on a mixed genetic background (B6;129), breeding heterozygotes together yielded less homozygous pups (~12.5%) than predicted Mendelian ratio. By 2016, The Jackson Laboratory live colony had been maintained by several generations of breeding heterozygotes together and/or to wildtype siblings (generation F39-40). In addition, some pedigree lines had been backcrossed 1-2 generations onto C57BL/6J (during rederivation, etc.). At that time, some instances were reported that heterozygous matings were failing to generate live homozygotes. Of note, the donating investigator reported that similar breedings using C57BL/6-congenic Scarb1tm1Kri (generation N9, not at The Jackson Laboratory) resulted in embryonic death of all homozygotes. Taken together, this suggests that mice homozygous for this Scarb1 knock-out allele have increased incidence of embryonic lethality associated with continued backcrossing onto C57BL/6. In response, The Jackson Laboratory will not maintain the pedigree lines backcrossed onto C57BL/6J. In 2017, re-establishment of a mixed B6;129 genetic background (closer to 50% C57BL/6 : 50% 129S1) resulted in heterozygous breeders producing homozygous offspring (both females and males) at ratios approaching Mendelian expectations. Of note, a similar strain, Srb1deltaCT (Stock No. <a href="https://www.jax.org/strain/032062">032062</a>), containing a premature stop codon in exon 12, is viable and fertile as homozygotes.

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Knock-out mice for the scavenger receptor class B, member 1 (Scarb1tm1Kri) exhibit increases in in plasma cholesterol (primarily HDL) as compared to wild type controls, and decreases in cholesterol levels in adrenal tissue.

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