Gene regulation in Cryptosporidium: New insights and unanswered questions

Parasites of the genus <i>Cryptosporidium</i> have evolved to have a highly compact genome of ∼9.1 Mb. The mechanisms that regulate gene expression in <i>Cryptosporidium</i> spp. remain incompletely understood at all levels, including chromatin accessibility, transcription factor activation and repression and RNA processing. This review discusses possible mechanisms of gene regulation in <i>Cryptosporidium</i> spp., including histone modifications, <i>cis</i> regulatory elements, transcription factors and non-coding RNAs. <i>Cryptosporidium</i> spp. are among the most basal branching apicomplexans and existing evidence suggests that they diverge from other members of their phylum <i>via</i> retention of the E2F/DP1 transcription factor family, and the recent discovery that <i>C. parvum</i> produces polycistronic transcripts. Most of what we know about gene regulation in the genus <i>Cryptosporidium</i> is based on sequence conservation and homology with other members of the phylum Apicomplexa, and in some cases, more distant eukaryotes. Very few putative gene regulatory components identified in <i>Cryptosporidium</i> spp. are supported by experimental confirmation. This review summarizes what we know about gene regulation in <i>Cryptosporidium</i> spp. and identifies gaps in our current understanding.