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Cleft beak induced by hydrocortisone in the chick is prevented by increased cell division after experimental
M Peterka1, R Peterková, Z Likovský
1Department of Teratology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague.
Insights
Hydrocortisone exposure in chick embryos causes cleft beaks by inhibiting mesenchymal cell mitosis. Releasing amniotic fluid via amniotomy reversed this effect, preventing hypoplasia and restoring normal beak development.
Area of Science:
- Developmental biology
- Teratology
- Embryology
Background:
- Hydrocortisone (HC) exposure in chick embryos on embryonic day (ED) 4 leads to medial nasal process hypoplasia by ED 5.
- This hypoplasia results in a high incidence (80-100%) of cleft beak by ED 9.
Purpose of the Study:
- To investigate the effect of hydrocortisone on cell proliferation in the medial nasal process.
- To explore the mechanism by which hydrocortisone induces cleft beak and potential interventions.
Main Methods:
- Intra-amniotic injection of hydrocortisone in chick embryos on ED 4.
- Evaluation of cell proliferation using BrdU labeling and mitotic index in medial nasal process epithelium and mesenchyme 24 hours post-injection.
- Assessment of cleft beak development and intervention via amniotomy on ED 5.
Main Results:
- Hydrocortisone significantly reduced mesenchymal cell proliferation and mitotic index compared to controls.
- Epithelial cell proliferation remained unaffected by hydrocortisone exposure.
- Amniotomy on ED 5, releasing amniotic fluid and hydrocortisone, significantly increased mesenchymal cell mitotic index within one hour.
- Amniotomy prevented the development of cleft beak in hydrocortisone-exposed embryos.
Conclusions:
- Hydrocortisone inhibits mesenchymal cell mitosis, leading to medial nasal process hypoplasia and cleft beak.
- The outflow of amniotic fluid and hydrocortisone via amniotomy releases mesenchymal cells from G2 phase arrest, restoring proliferation.
- Amniotomy serves as a potential intervention to prevent hydrocortisone-induced developmental defects like cleft beak.
Abstract:
Hypoplasia of the medial nasal process has been reported in chick embryos on embryonic day (ED) 5, 24 h after their exposure to hydrocortisone (HC). As a result, the cleft beak occurs in 80-100% of specimens on ED 9. In order to analyze its influence on cell proliferation, HC was injected intra-amniotically into embryos on ED 4, and the mitotic index and number of BrdU-positive cells were evaluated 24 h later, both in the epithelium and mesenchyme of the medial nasal processes, on serial frontal histological sections. Two hours after BrdU administration, there were 50% of labeled mesenchymal cells in the embryos exposed to HC and only 23% in the control group. The mitotic index of mesenchymal cells was significantly lower in the HC group than in the controls. The epithelium showed no significant difference. HC seemed to prevent the mesenchymal cells from entering mitosis. The cleft beak in the embryos exposed to HC on ED 4 was totally eliminated by tearing open the amnion (amniotomia) and allowing fluid to leak out on ED 5. In some of specimens exposed to HC, the mitotic index was investigated at six time intervals from 15 to 120 min after amniotomia. A significant increase in the mitotic index was detected in the mesenchymal cells of the medial nasal processes during the first hour after amniotomia. Such a prompt increase of the mitotic activity may be hypothetically explained by release of the HC from its receptor binding as a consequence of outflow of the amniotic fluid together with the HC pool, and freeing of the mesenchymal cells, blocked in the G2 phase, to enter mitosis. As a result, the hypoplasia of the medial nasal process might be compensated and the development of the cleft beak prevented.