Epigenetically regulated genomic expressions for shortened stature and cleft palate are regionally specific in the 11-day mouse embryo.

Abstract

Chronokinetic synergism, a holistic and extremely sensitive experimental design, has shown in the mouse embryo that site-specific epigenetic forces differentially regulate genesis of the palate (cleft palate) and limb bud organogenesis (shortened stature). Acute exposures of 11-day pregnant mice to minimally effective doses of thymidine or ethanol followed 5 or 8 hr later by minimal exposure to retinoic acid have enabled quantitative and qualitative assay for genomic-epigenetic interactions. These site-specific morphogenetic regulations occurred during palatal genesis from the maxillary prominence of the first pharyngeal arch and during limb bud prechondrogenesis. Thymidine is presumed to induce its response by inhibition of DNA polymerase and hence by transitory cytostatic block. (Embryo size was not detectably changed). Ethanol is interpreted, guilt by associated response, indirectly to interfere with histone regulation of transcription. Two central findings have demonstrated the coordinated regulation of genomic and epigenetic positional information. First, thymidine or ethanol as epigenetic probes for limb prechondrogenesis and palatal precursor cells have activated distinctive site-specific responses. Second, responses to chronokinetic synergisms have indicated that epigenetic regulators for limb and palate dysmorphogenesis may affect distinctly different phases of the cell division cycle and hence induce differential DNA expressions. Although each of palate and limb is concurrently susceptible to epigenetic regulation, their differential intrinsic genomic capabilities appear to have been uncoupled. The putative homeostatic balance of genomic expressions in the palate precursor and the prechondrogenic limb bud cells of the 11-day mouse embryo has been characterized as epigenetically regulated, alternatively expressed, and positionally restricted. We propose that the chronokinetic synergisms have disclosed the existence of distinctive palate-determining genes and stature-determining genes.