Do you know if the promoters in the GIPZ/TRIPZ vectors will be active in the developing mouse embryonic brain?

Yes, the CMV promoter is active in the developing mouse brain. There are now plenty of papers using GIPZ in these neuronal cell types. In fact one of the initial papers (not using shRNA though) showing efficacy of this promoter in the developing mouse brain is the one below: Efficient in utero gene transfer system to the developing mouse brain using electroporation: visualization of neuronal migration in the developing cortex Neuroscience, Volume 103, Issue 4, 4 April 2001, Pages 865-872 H. Tabata and K. Nakajima Another paper which should help alleviate any concerns is below: Dlg1, Sec8, and Mtmr2 regulate membrane homeostasis in Schwann cell myelination. J Neurosci. 2009 Jul 8;29(27):8858-70. Bolis A, Coviello S, Visigalli I, Taveggia C, Bachi A, Chishti AH, Hanada T, Quattrini A, Previtali SC, Biffi A, Bolino A.