Deletion of Htt cause alterations in cAMP signaling and spatial patterning in Dictyostelium discoideum

Abstract

In the present study, we have analyzed in detail the functions of Htt during growth and development of the protist, Dictyostelium discoideum by creating mutants (both overexpressor and knockout). The mRNA was present at all stages of growth and development. Overexpression of htt did not show any major anomaly, while deletion resulted in delayed aggregation territory formation and showed asynchronous development especially after slug stage. The slugs formed by htt − cells showed aberration in anterior–posterior boundary, showing increased prestalk region. DdHtt regulates STAT transcription factors in the tip organizer region that help maintain patterning and culmination. In chimeras with the wild‐type, htt − cells preferentially localized to the tip of the slug and basal disc regions of the fruiting body showing prestalk/stalk bias, while the overexpressing cells majorly populated the prespore/spore region showing spore bias. These differences could be attributed to protein kinase A (PKA)‐regulated cyclic adenosine monophosphate (cAMP) signaling.

Dictyostelium discoideum: A Model System for Neurological Disorders

“…The authors then examined the expression of STAT transcription factors and noted a decrease in the expression of STATs involved in the decision to proceed with slug migration or culminate. Together this data shows that Htt is required for proper patterning and maintenance of stalk and spore cell boundaries [81].…”

“…Htt in D. discoideum functions in growth and development, but unlike in higher eukaryotes where it is embryonically lethal, D. discoideum Htt − mutants are viable. When Htt − cells were grown in adherent culture their growth rate was unimpaired [79] but when grown in an axenic shaking culture they grew slower than the wild type parental strains [81]. This difference in ability to grow in different media was found to be due to a defect in the EDTA-resistant cell adhesion properties in shaking culture.…”

“…Using chimeras, Myre et al [79] showed that htt null cells in the presence of wild type cells would not populate the prespore region and consequently did not end up in the spores. Furthermore, Bhadoriya et al [81], using LacZ reporter fusion and neutral red staining demonstrated a misregulation of spatial expression of prestalk cells. Conversely, the expression of prespore cells was the same as the wild type until it reached the slug stage and its expression significantly increased in the htt mutant.…”

“…Thompson et al [84] showed that the speed and accuracy of chemotaxis is reduced in the htt − mutant [84]. Bhadoriya et al [81] analysed cAMP signalling in htt − cells by measuring cAMP protein levels and levels of transcripts of key genes. They noted a reduction in absolute cAMP levels during all stages of development with no characteristic increases during starvation or in the loose aggregate stage.…”

Dictyostelium discoideum as a non‐mammalian biomedical model

“…Dictyostelium represents a good model to study this disease since it has a huntingtin human orthologue whose mutation or deficiency is not lethal for the cells (Myre, 2012). Dictyostelium htt mutant cells show pleiotropic defects such as reduced cell–cell and cell‐substratum adhesion, delayed development, a strong cellular sensitivity to osmotic stress, cytoskeletal defects, chemotaxis defects and regulate cell fate during development (Thompson et al ., 2014; Bhadoriya et al ., 2019). These pleiotropic defects are consistent with the in vitro observations using human cells from Huntington’s disease patients (Bozzaro, 2013).…”