Figure 3: Expression analysis of 5′ variable exons of M. martensii sDscam.

(a) Relative expression levels of sDscamα and sDscamβ1–6 transcripts in different tissues. The expression level for each transcript is shown as reads per million (r.p.m.) of its corresponding constitutive exons. Data are expressed as a percentage of the mean±s.d. from two independent experiments. (b) The relative inclusion frequency of the sDscamα variable exon in different tissues. Alternative exon 2 was selected to calculate the level of expression. (c) The relative frequency of the variable exon clusters of sDscamβ1–6. Variable cassette 4 of sDscamβ1 was abundantly expressed in the cephalothorax (shown as the black arrow), but was barely detectable in other tissues. sDscamβ3 variable cassette 11 was abundantly expressed in the poison gland (shown as the blue arrow), but was barely detectable in other tissues. The 25-nt fragmented RNA-seq data sets were mapped to calculate the relative expression level. These results based on 25-nucleotide (nt) mapping were consistent with those based on 50-nt mapping, except for some very lowly expressed tissues (Supplementary Fig. 7).