Embryo genome transcripts contribute to the increase in ornithine decarboxylase activity required for gastrulation

Cloning and molecular characterization of an ornithine decarboxylase gene and its expression during embryonic development of the housefly, Musca domestica

We are interested in identifying targets that may be used to develop new control products for the common housefly, Musca domestica, a vector of disease for many vertebrates. One such target, ornithine decarboxylase (ODC), is an embryonic enzyme involved in the regulation of polyamines and is a critical enzyme during M. domestica development. In this study, the cDNA for ODC from M. domestica was cloned, sequenced, and characterized. The full-length cDNA was 1,337-bp, consistent with a single band of approximately 1.35 kb obtained by northern analysis. The open-reading frame contains 1,191 bp, yielding a deduced polypeptide of 396 amino acid residues with a predicted mass of 44,618 Da. The deduced M. domestica ODC protein was homologous to other ODC proteins. mRNA expression profiles analyzed by real-time PCR indicated that the ODC transcript is temporally regulated throughout embryogenesis. Sequence data and Southern blot analysis suggests that there were likely only one or two closely linked copies of the M. domestica ODC gene.

Quantification and localization of ornithine decarboxylase in the embryonic palate

Ornithine decarboxylase (ODC; EC4.1.1.17), the key enzyme in polyamine biosynthesis, and intracellular polyamines increase rapidly and markedly in tissues and cells that are actively proliferating as well as differentiating and decrease as these processes cease. ODC activity has also been implicated as playing a role in the proliferation and differentiation of cells derived from the developing palate. Ornithine decarboxylase activity was thus quantified and ODC localized in the developing murine palate in vivo. Levels of ODC activity showed little variation during the ontogeny of the palate, averaging 126 pmol CO2/mg protein/hr. When difluoromethylornithine (DFMO), an irreversible inhibitor of ODC activity, was administered to pregnant mice throughout the period of palate development (days 11-14), palatal tissue ODC activity was reduced by 85%. No craniofacial malformations were observed, however. The lack of a teratogenic effect by DFMO treatment could be due to sufficient remaining ODC activity in craniofacial tissue and/or maintenance of intracellular polyamine levels by the activity of a polyamine transport system. The activity of this system was demonstrated by the ability of palatal tissue in vivo to take up radiolabeled putrescine. The presence of a polyamine transport system was previously suggested by the demonstration of such a system in palate mesenchymal cells in vitro. Dramatic temporal and spatial shifts in tissue patterns of immunolocalization for ODC in developing palatal tissue were also seen. Immunostaining for ODC was evenly distributed in oral, nasal, and medial edge palate epithelial cells on day 12 of gestation. The basal aspects of epithelial cells were, however, more intensely stained. Mesenchymal cells exhibited a peri-nuclear immunostaining pattern. On days 12 and 13 of gestation, the staining patterns for ODC in palate epithelial and mesenchymal cells were comparable. On day 14 of gestation, all regions of the palate epithelium, particularly the medial edge epithelia, were immunostained for ODC, whereas the intensity of staining in the mesenchymal cells was significantly reduced. This study represents essential initial observations toward understanding the role that ODC may play in normal craniofacial development.

Ornithine decarboxylase inhibitors and fetal growth retardation in mice

Putrescine (PUT) and the putrescine analogues, 1,3-diaminopropane (DAP) and 1,6-diaminohexane (DAH), were administered to pregnant female mice during the time of maximal fetal ornithine decarboxylase (ODC) activity, days 10-14 of gestation. Such treatment resulted in an inhibition of fetal ODC activity, as measured 2 hours later, and a proportional decrease in fetal weight, as measured on day 18 of gestation. The order of effectiveness for these compounds was DAP greater than DAH greater than PUT. Neither DAP nor DAH nor PUT were fetocidal nor maternally lethal under the treatment regimen employed. The generality of the effect of these compounds, i.e., the retardation of fetal growth and the lack of gross malformations, is consistent with the hypothesis that they are interfering with a primary process, probably protein synthesis. The restricted time span of effectiveness implies that these compounds are specific inhibitors of ODC and that decreased ODC activity is producing an effect on growth.

Inhibition of rat ovarian ornithine decarboxylase by ethanol in vivo and in vitro

Intragastric administration of ethanol greatly inhibited ovarian ornithine decarboxylase (L-ornithine carboxy-lyase EC 4.1.1.17) stimulated by human chorionic gonadotropin in vivo. The inhibition occurred only if the treatment with ethanol was started before the injection of hormone. The use of inhibitors for alcohol dehydrogenase and aldehyde dehydrogenase clearly showed that the observed inhibition was a direct effect of ethanol itself. When rat ovarian cells were incubated in vitro with human chorionic gonadotropin the activity of ornithine decarboxylase was also markedly stimulated. This stimulation could also be inhibited by ethanol. Moreover, actinomycin D and alpha-amanitin inhibited the stimulation of ornithine decarboxylase, showing that the enhanced activity in vitro resulted from the synthesis of new mRNA for ornithine decarboxylase. The time dependence of the inhibition caused by ethanol addition resembled that after addition of actinomycin D. This supports the view that one site where ethanol inhibits protein synthesis is at the transcriptional level.