Fig. 2. BDNF expression in B/N mutant mice. (A-C) Northern blot analysis of BDNF transcripts in tissues dissected from newborn wild-type (WT) and B/N mice. For each sample, 10 µg of total RNA were analyzed. The NT3-coding sequence used to probe the wild-type samples identified a unique 1.4 Kb band (A). Hybridization of the B/N tissues with the NT3 probe resulted in the total absence of signal, as expected (not shown). Hybridization of the WT samples with the BDNF cDNA probe identified the expected 1.6 and 4.0 kb bands corresponding to the endogenous products of the Bdnf gene (B) (Maisonpierre et al., 1990). Hybridization of the B/N tissues with the BDNF probe revealed, in addition to the endogenous BDNF-specific pattern of expression, an additional band (B/N) of approximately 1.4 kb (C). Note that the pattern of expression of the recombinant BDNF (B/N) parallels that of NT3. Blots were hybridized with a cyclophilin-specific probe to assure equal RNA loading (not shown). B.A.T., brown adipose tissue. (D-K) BDNF replaces NT3 expression in the mutant B/N mouse at the cellular level. In situ hybridization analysis of NT3 and BDNF expression in wild-type and B/N animals during embryonic development. Transverse dark-field views of wild-type (D-G) and B/N (H-K) embryos at embryonic stage E11.5 (D,F,H,J) and E13.5 (E,G,I,K) hybridized with an NT3- (D,E,H,I) or BDNF-specific (F,G,J,K) probe. Note the precise replacement of NT3 specific signal in the lateral motor column (arrows) of the wild-type spinal cord (D,E) by BDNF hybridization in the B/N mutant. (J,K).