tokens: Southern hybridization of genomic DNA from WT and Lp / Lp embryos failed to identify specific rearrangements at or near the Nhlh1 locus , and Northern RNA blotting and RT - PCR evaluation of Nhlh1 mRNA expression indicated that both the levels and types of Nhlh1 mRNAs produced in WT and Lp / Lp embryos were indistinguishable .