Caudalization by retinoic acid is correlated with inhibition of cell population growth and expansion of chick blastoderms cultured in vitro.

Full primitive streak stage chick embryos, cultured in vitro for 20 h in the presence of 10(-9) to 10(-7) moles of retinoic acid (retinol, all-trans), exhibit increasing extent of malformations. RA causes caudalization, suppression of telencephalon, formation of open and enlarged neural tube in the regions of midbrain, hindbrain and spinal cord, failure of fusion of heart tubes, and gives rise to winged or diffused, and even supernumerary somites. Extreme abnormalities include failure to form the head fold and foregut.

Multiple neural inductions in area opaca by grafts of the Hensen's node do not retard host chick embryo development.

Four hundred and forty four full primitive streak stage chick embryos were cultured in vitro and 261 were transplanted with 1, 3 or 5 Hensen's nodes in the area opaca. Irrespective of the number of grafts, neural induction was observed in 90% cases. The development of control and grafted embryos and the size of blastoderm area were monitored at the time of grafting and after 20 hr.

Lithium Chloride and Trypan Blue Induce Abnormal Morphogenesis by Suppressing Cell Population Growth: (LiCl/trypan blue/chick teratogenesis/cell population growth inhibition).

Full primitive streak stage chick embryos were cultured in vitro for 20 hrs and monitored every 4 hr for morphology, cell number and blastoderm area. In normal embryos, the cell population growth is exponential and correlates directly with Increasing morphological rank. The chick blastoderm area expands in two waves, one immediately after gastrulation and another after 16 hr in culture, while cell population growth is predominant between 4-16 hr.

Cell Population Growth and Area Expansion in Early Chick Embryos During Normal and Abnormal Morphogenesis in vitro: (trypan blue, chick embryo/teratogenesis/cell population growth/blastoderm expansion).

The exponential growth and cell population during the early embryogenesis of chick, cultured in vitro correlates with a linear increase in the blastoderm area. To understand the relationship between these parameters and normal morphogenesis, we have used a known teratogen, trypan blue, as a probe. A method is developed in which each new embryonic structure is assigned a rank value of 1 and the total number of ranks allows quantification of development and establishment of a numerical relationship between the size of the cell population, blastoderm area and the morphological development.

Cell population growth in chick blastoderms cultured in vitro.

Primitive streak stage chick blastoderms were cultured in vitro up to 30 hr by New's technique. Chick blastoderms reaching stages 4 to 12 in vitro cultures and in ovo were harvested and homogenized to release cell nuclei. Fluorescent ethidium bromide-stained nuclei in homogenates were counted in Neubauer's chamber and the size of total blastoderm cell population was determined.