Anatomical defects associated with a feathering mutant (Ottawa naked) in domestic fowl.

An autosomal recessive mutation (Ottawa naked, nk) that causes abnormal feathering, fusion of the third and fourth toes, and low viability has been reported previously in the chicken. In the present study mutant individuals were examined from three different stocks: the original one in which the mutant was found and two outbred F2 stocks. Defects of the tail region were observed in all mutants from the original stock (20/20) and in 64% (16/25) of the mutants produced from the outcrossed stocks. The severity of the defects ranged from mild distortion and scoliosis of the coccygeal vertebrae to absence of all vertebrae from the lumbosacral level caudad. Forty percent (16/40) of the mutants from the original stock lacked caudal portions of the kidneys to varying degrees. Edematous areas were observed in 22% (15/67) of the embryos examined at 14 days of incubation. Other defects observed in the mutant embryos but not studied in detail are abnormal patterning or absence of scales, absence of the caudal spinal cord in embryos with severe rumplessness, and failure of the three metatarsal bones to fuse into a single element. Since all structures affected in the mutants differentiate primarily from or may be dependent upon the mesoderm, it is suggested that the site of gene action lies within this germ layer. A decrease was observed in both incidence and severity of the various defects following outcrossing, which suggests the presence of modifiers that influence the expression of the trait.

Effect of osmotic pressure on neurogenesis in cultures of chich embryo spinal cords.

The osmotic pressure of the medium in stoppered, roller tube cultures increased by an average of 17 +/- 6 mOsM per kg of water during 3 days of incubation at 37 degrees C irrespective of the initial osmolality (280 to 340 mOsM) of the medium. The increase was apparently due to evaporation of water from the medium into the gas phase of the roller tube. This observation led us to study the effect of osmotic pressure on neuronal differentiation in cultures of chick embryo spinal cords. Spinal cords were excised from stage 16 to 19 (2.5 to 3 days of incubation) or stage 36 (10 days) chick embryos and cultured as fragments on collagen-coated cover slips in roller tubes at 37 degrees C for 21 days. The medium was adjusted to 283 +/- 3,300 +/- 3,323 +/- 3, or 342 +/- 3 mOsM per kg with saturated choline chloride solution or distilled water. The results indicate that the nature of the neuronal differentiation in vitro was not altered by the osmolality of the medium. The proportion of cultures containing neurons was influenced by osmolality. In the 300 +/- 3 mOsM medium, 75% of all the stage 36 cultures initiated contained neurons, and 52% of all the stage 16 to 19 cultures initiated contained neurons. In the other media the proportion of neuron-containing cultures was lower. Two conclusions were drawn. Neurogenesis in cultures of embryonic chick spinal cord fragments is sensitive to an increase in the initial osmotic pressure of the medium as small as 20 mOsM above the optimal 300 mOsM. As a result of the 17 mOsM increase which always occurred in the culture medium between feedings, the optimum osmolality for neuronal development is in fact a range, from 300 to 317 mOsM.