 While the molecular target for these non-genomic effects of nuclear receptors has not been conclusively demonstrated, it has been hypothesized that there are variants of nuclear receptors which are membrane associated instead of being localized in the cytosol or nucleus.Furthermore, these membrane associated receptors function through alternative signal transduction mechanisms not involving gene regulation.While it has been hypothesized that there are several membrane associated receptors for nuclear hormones, many of the rapid effects have been shown to require canonical nuclear receptors.