Identification of Common Genomic Motifs in the Promoter Sequences of Cryptosporidium hominis

In the last two decades, scientists have become increasingly aware of the global impact on human populations of protozoan intestinal parasites from the genus Cryptosporidium. The two species, Cryptosporidium hominis and Cryptosporidium parvum, have been detected in surface waters around the world and constitute a significant global health risk.

The species of the genus Cryptosporidium enter their hosts as thick-walled oocysts through the fecal-oral route. Because of this, infection is generally the result of contaminated water. These oocysts break open in lower gastro-intestinal tracts of their hosts and proceed to infect the epithelial cells of the intestinal wall by using a specialized organelle called an apical complex. It is there, within the intestines of their hosts, that the Cryptosporidium species complete their life cycles, reproducing asexually as well as sexually. This reproduction produces the next generation of oocysts that are capable of spreading the infection when passed through the host’s stools.

Infection by the Cryptosporidium species results in acute gastro-enteritis with symptoms including diarrhea, fever, weight loss and vomiting. These symptoms can be quite intense and debilitating. The incubation period has been shown to be between one and twelve days in most individuals, with an average incubation period of seven days. Symptoms are often severe for a week or more. Most healthy individuals are symptom-free after two weeks. People with undeveloped or compromised immune systems are at the greatest risk from the Cryptosporidium species. People with AIDS are particularly at risk. In them, an infection by the Cryptosporidium species can easily be fatal.

Because of the threat to world health posed by this parasite, it is imperative to learn everything we can about it. In this study, we will focus on the promoter regions upstream of the genes identified from the sequenced genome of Cryptosporidium hominis. These promoter regions regulate the expression of genes by binding specific proteins called transcription factors. These transcription factors alter the chemical environment just upstream of the transcription start point, making RNA polymerase more likely to bind. We hope to find unique motifs within the promoter regions of known Cryptosporidium hominis genes. This could lead to identification of transcription factors unique to Cryptosporidium hominis which might make excellent targets for new drugs.

Methods:

We will be analyzing the genome of Cryptosporidium hominis using genomic data from the biolingua server. Looking upstream of the known genes for common promoter sequences, we will locate the basal promoter, the TATA box, and other common promoter sequences, CAAT and GC boxes. We will then continue looking at the upstream promoter regions of genes to see if we can locate any previously unknown binding sequences, paying particular attention to any palindromic sequences we might find. We might also consider using one of the many programs available on the internet either to actually find sequences or to come up with methods of locating them.

Possible Results and Implications:

Hopefully, this study will result in detection of novel promoter sequence motifs that occur only within the genome of Cryptosporidium hominis. From these sequences, information about the regulatory proteins that bind to them could be inferred. Further studies could then be conducted to determine the physical and chemical nature of the proteins.

With knowledge about the regulatory proteins’ shape, composition and chemical properties, new pharmaceuticals could be developed to bind specifically the proteins unique to Cryptosporidium. These drugs could significantly shorten the course of infection and reduce the severity of symptoms. With a shortened timeframe, it also makes sense that the parasite would be much less likely to be spread from person to person. The host would pass fewer oocysts in a shortened timeperiod and would be more likely to pass those few oocysts in closer proximity to where the parasite was first contracted, limiting the parasites access to new hosts.

Considering the ubiquitous nature of the pathogen, and especially its prevalence in heavily populated nations with high levels of HIV infection, anything that could treat infection by the Cryptosporidium species would be an incredible boon to worldwide health.