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Fig. 1. RetDN/+ mice fail to thrive. (A) Mutant or wild-type
human RET9 cDNA was introduced into exon 1 (black box) of the mouse
Ret locus (black triangles, loxP sites). The restriction
sites (K, KpnI; N, NcoI) and length of the expected
fragments in Southern blots are indicated. (B) Schematic of Ret knocked-in
alleles. Open box, RET9 cDNA; black line, SV40 3'UTR; ECD, extracellular
domain; TK, tyrosine kinase domain; triangle, loxP sites; L985P and Y1062F,
RET mutations in the DN allele. (C) Southern blot analysis confirmed
successful generation of Ret mutant mouse lines. (D) Growth curves of
RetDN/+ and wild-type (wt) littermates at indicated
postnatal time points (n=3 for each time point;
*=P<0.01; error bars, mean±s.d.). (E) Photograph
showing the typical size difference between 3-week-old
RetDN/+ and wild-type littermates. (F) Expression of Ret
mutant alleles in mouse brain RNA (P0) by RT-PCR. Total, endogenous mouse and
knocked-in human RET; knockin, mice harboring the indicated human RET
cDNA (Ret9 or RetDN) in the Ret locus generate a knockin-specific
product; knockout, RetTGM mice where the ret locus is
inactivated with the TGM allele. Note that retention of the neomycin
resistance gene (RetDNneo/+) results in a marked reduction
in expression of the knocked-in RetDN allele. wt, wild type. cDNAs knocked-in
in the ret locus: RetDN, mutant human RET9 (L985P,
Y1062F); Ret9, human wild-type RET9; RetTGM,
tauEGFP-myc; RetDNneo, retained neomycin resistance gene in
RetDN allele. `+' denotes one copy of the endogenous mouse
allele.