In birds, for example, the minimal essential MHC in chicken consists of 19 genes [ 6] while gene duplications have expanded this region in quail [ 7] and sparrows [ 8].
This "minimal essential" MHC structure for chicken (Kaufman et al. 1999), with its lack of redundancy and tight linkage between genes, may have important implications for the role of the MHC in disease resistance, because it results in much stronger associations between particular MHC genotypes and disease resistance or susceptibility (Kaufman 2000, 2013).
In sharp contrast to mammals with multiple class I and II loci, the avian model organism, the chicken has a "minimal essential Mhc", a term referring to its surprisingly small, densely packed Mhc region with only two class I and II genes [ 14, 15].
In some birds, it consists of only a small number of linked MHC core genes (e.g. smaller than 20 in chickens) forming a minimal essential MHC and, in fish, the MHC consists of a so far unknown number of genes including non-linked MHC core genes.
The chicken was described to have a "minimal essential" MHC containing a single dominantly expressed MHC Class I locus [ 23].
Bone marrow cells were isolated from the femur and tibia of 8 to 10-week-old female C57BL/6 J-TgN mice (The Laboratory Animal Center of The Academy of Military Medical Sciences, Beijing, China), transgenically expressing the chicken β-actin-EGFP gene, by flushing with Iscove's minimal essential medium (IMEM).
Some species, such as chicken or parrots, have an extremely small, compact MHC, dubbed "the minimal essential MHC" [ 28, 29].
Cells were maintained in alpha minimal essential medium (Gibco-BRL,Gaithersburg, MD, USA) supplemented with 10% (v/v) fetal bovine serum, 1% (v/v) normal chicken serum, 100 µmol/l β-mercaptoethanol (Sigma-Aldrich, St Louis, MO, USA), 100 units/ml penicillin and 100 μg/ml streptomycin (Gibco-BRL), at a maximum density of 1 × 106 cells per ml.
Avian MHC organization is of particular interest because the chicken Gallus gallus, the avian species with the best characterized MHC, possesses a highly streamlined minimal essential MHC, which is linked to resistance against specific pathogens.
"Quitman is down to those minimal essential services it's essential to have to run a county -- the county library, the county school," she said.
