The Hand2fl allele has loxP sites flanking exon 1 of the Hand2 gene. Because the PGK-neo cassette is not present in this allele, heterozygotes (Hand2fl/+) and homozygotes (Hand2fl/fl) are viable and fertile with no alterations in Hand2 expression levels/patterns (in situ hybridization and qRT-PCR) compared to wildtype mice. Homozygotes exhibit no reported abnormal phenotype.
Hand2 is a basic helix-loop-helix family transcription factor that functions in sympathetic nervous system morphogenesis and cell type-specific gene expression in sympathetic, enteric and adrenal chromaffin cells, cardiac morphogenesis and limb bud / branchial arch development.
The absence of Hand2 expression may also be a useful biomarker for atypical hyperplasia, endometrioid carcinoma and epigenetic silencing.
When Hand2fl mice are bred to Cre recombinase-expressing animals, the resulting offspring may be useful in generating global Hand2 knockout mice or tissue-specific Hand2 knockout mice. Specific examples are described below.
When bred to germline Cre-expressing mice, the resulting Hand2 global knockout homozygotes (Hand2ko or Hand2Delta) are embryonic lethal around embryonic day (E)10-12, with some surviving to birth but expiring thereafter.
Breeding Hand2fl mice to Wnt1-Cre transgenic mice (Stock Nos. 003829 / 009107) results in deletion of Hand2 expression in neural crest cells. The resulting Hand2cko homozygotes exhibit reduced neuronal precursor cell/neuroblast proliferation and neuronal numbers, abnormal facial/skull development and aglossia (absence of a tongue), with no gross cleft palate. Hand2cko mice also have neurogenesis defects/decreased neurons in the developing enteric nervous system with few to no noradrenergic sympathetic ganglion neurons.
Deletion of Hand2 expression in neural precursor cells using Nestin-Cre transgenic mice (Stock Nos. 003771 / 019103) is lethal at around postnatal day (P)20, allowing analysis throughout development and the early neonatal period. Such mice have abnormal enteric nervous system development with loss of all nitergic neurons, decreased numbers of cholinergic neurons and functional aganglionosis.
