To identify the sequence of the hatching enzyme in A. callidryas, we created a BLAST database of the assembled transcriptome of hatching-competent,5-day-old A. callidryas embryos (data available upon request). We searched the database using the Xenopus laevis hatching enzyme transcript (‘XHE’ or ‘UVS.2’;GenBank D89632.1) and found one homologous contig. We then used gene-specific primers (forward primer, 5′-ACAACATGGGCGAGAAGATTTA-3′;reverse primer, 5′-TGAAGTTTCCTTGTGGTGTGATA-3′) to amplify the transcript from reversetranscribed complementary DNA from hatchingcompetent A.callidryas embryos. The product was cloned into pGEM T Easy (Promega) and transformed into XL-1 Escherichia coli for amplification; plasmids were purified for sequencing and probe synthesis using Qiagen miniprep and maxiprep kits. The A.callidryas hatching enzyme (‘AcHE’, GenBank accession number KY924327) sequence and amino acid sequence alignment are reported by Cohen et al.(2018). After linearization with SacII, the plasmid was used to synthesize a digoxigenin-labelled anti-senseRNA probe using the SP6 RNA polymerase. Our probe encompassed 1124 bp of sequence complementary to the target mRNA. Our probe sequence covered both a zinc metalloprotease active site and one of the CUB domain repeats common to amphibian hatching enzymes (Nagasawa et al., 2016). Nucleotide BLAST analysis on the probe sequence returned only the X. laevis hatching enzyme and no other protein or enzyme. In addition, phylogenetic analysis showed that the A. callidryas hatching enzyme transcript was more similar to hatching enzymes from frogs and fishes than it was to any other proteins from the astacin-like metalloprotease family M12A (Cohenet al., 2018).