A targeting vector was designed to replace the C-terminus DNA-binding domain of transcription factor 4 (Tcf4 or E2-2) gene with a neomycin (neo) selection cassette. Homozygotes are born at a low frequency and die within the first week of life. E2-2 is a widely expressed E2A-related helix-loop-helix (HLH) protein required for the generation of normal numbers of pro-B cells in mouse embryos. While homozygous E2-2 mutant embryos are capable of making B cells, they produce only half as many as wildtype. Mice heterozygous for the mutation are viable, fertile, and normal in size. This strain may be useful for studying B cell development, activation of differentiation of a subset of neural progenitors, and neurodevelopment associated with Pitt-Hopkins syndrome (PHS).
 When crossed to mice containing a (Atoh1)-lacZ transgene, &beta;-galactosidase staining is evident in anterior extramural migratory stream (AES) cells which accumulate in the region lateral to the pontine nucleus. The resulting mice exhibit a reduction in size of the pontine nucleus and a lack of migration of neuronal precursors to the region of the pontine nucleus.

Homozygotes for this knock-out mutation of the Tcf4 gene are born at a low frequency and die within the first week of life. When still viable, mice have a diminished capacity to generate B cells.

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