Tissue-Specific Gene Expression
Specific pattern and level of expression of a transgene (Cre or Flp recombinase, reporter genes, safe harbour, target gene, etc.) are key parameters of relevant transgenic models.
Knocking in the transgene, which means targeting its insertion into one specific and predetermined location of the genome, enables the optimal regulation of its expression. The complete endogenous mouse promoter (all regulatory elements being present, included enhancers and repressors located kilo bases away) will control the transgene regulation.
This Knockin technology has become the gold standard technology for tissue-specific expression since it enables to determine the transgene expression pattern and its level of expression. Many types of models have been created including:
- Tissue-specific expression of Cre and Flp recombinase (⤏ see also site-specific recombination)
- Monitoring gene expression using a reporter gene like fluorescent proteins (⤏ see also reporter mice, or cell lines)
- Inserting transgene in a safe harbour like Rosa26, Hprt locus (⤏ see also Quick Knockin mice, or cell lines)
- Humanizing the gene of interest (⤏ see also humanized Knockin mouse models)
Case study 1: Repopulation kinetics of intestinal stem cells in tamoxifen-inducible Cre mice.
Adapted from Sangiorgi et al. Nat Genet 2008. Bmi1 is expressed in vivo in intestinal stem cells.
Expression Obtained in the Targeted Subpopulation
Bmi1+ expressing Cre+ cells repopulate crypts of the small intestines.
Cre function is detected (lacZ staining) in the Bmi1+ cell lineage.
Repopulation starts day 2 (a) after tomoxifen injection. First fully labelled crypts are visible at day 17 (i).
Case study 2: Neurons and oligodendrocytes Cre recombinase-specific expression.
Adapted from Battiste et al. Development 2007. Ascl1 defines sequentially generated lineage-restricted neuronal and oligodendrocyte precursor cells in the spinal cord.
Expression Obtained in the Targeted Cell Lineage
Ascl1 expressing Cre+ cells give rise to neurons and oligodendrocytes.
Cre function is detected (lacZ staining) in developing sympathetic neurons.
Expression is just beginning at E10.5 but is clearly evident by E11.5.
Case study 3: Salivary gland Cre recombinase-specific expression.
Adapted from Bullard et al. Dev Biol 2008. Ascl3 expression marks a progenitor population of both acinar and ductal cells in mouse salivary glands.
Expression Obtained in Biomarker Expressing Cells
Cre recombinase expression recapitulates endogenous Ascl3 expression.
Arrowheads indicate duct cells of the submandibular gland in which Ascl3 expressing Cre+ cells are labeled red using antibodies to Cre recombinase.
Ac, acinar cells; Du, duct cells.