Nycodenz gradient analysis of 18S ribosomal RNA, and the Ldhc and Smcp mRNAs in 26 dpp prepubertal mouse testis. A cytoplasmic extract of the testes of three 26 dpp mice was sedimented on a Nycodenz gradient, collected as 19 fractions from the bottom, RNAs were extracted from each fraction, and the levels of 18S rRNA, Ldhc and Smcp mRNAs were determined by sequential hybridization of each probe to a Northern blot and phosphorimage analysis. The methods and probes are described in the Additional file 1 and . 18s rRNA, blue triangles; Ldhc mRNA, black squares; Smcp mRNA, red circles. The peaks of polysomes and free-mRNPs are indicated.