146 



The Nucleus and Cytoplasm in Development 



and T. palmatus nucleus (de Roche, '37). 

 Transplantation of neural crest containing 

 T. rivularis cytoplasm and T. torosus nu- 

 cleus to diploid T. torosus hosts produced a 

 pigment pattern essentially like that of T. 

 torosus; however, an influence of the cyto- 

 plasm of the donor species T. rivularis was 

 manifested in the rate of melanization of the 

 pigment cells (Dalton, '46). 



POLYPLOID SPECIES HYBRIDS 



A few observations have been made on the 

 combined effects of polyploidy and hybridiza- 

 tion ("allo-polyploidy" of the plant geneti- 

 cists), an experiment which offers interesting 

 possibilities. Eggs of sea urchins activated 

 by carbon dioxide or ammonia pass through 

 one or more monaster cycles, doubling or 

 quadrupling the haploid chromosome num- 

 ber of the egg. Following fertilization with 

 sperm of another species, triploid (and pos- 

 sibly pentaploid) species hybrids are pro- 

 duced which show a preponderance of ma- 

 ternal characteristics (Herbst, '12; Hinderer, 

 '14; Landauer, '22). Triploid species hybrids 

 have also been prodviced by mating triploid 

 Drosophila mclanogaster with diploid D. 

 simulans for a stvidy of interspecific sterility 

 (Schultz and Dobzhansky, '33). In amphib- 

 ians triploid hybrids with two sets of mater- 

 nal chromosomes may be produced easily 

 by refrigeration of eggs, which svippresses 

 the formation of the second polar body (T. 

 rivularis $ X T. torosus $ , Costello, '42; 

 T. palmatus $ X T. alpestris $ , Fischberg, 

 '48). In the latter experiment, the hybrid 

 larvae with two sets of T. palmatus and one 

 set of T. alpestris chromosomes exhibited a 

 predominantly T. palmatus pigment pattern, 

 in contrast to the diploid hybrids which 

 showed a preponderance of T. alpestris char- 

 acteristics. Closer resemblance to the maternal 

 species was also found in triploid hybrids T. 

 pyrrhogaster X T. ensicauda and Rana 

 japonica X R. temporaria ornativentris 

 (Kawamura, '52a,b). 



OTHER EXPERIMENTAL APPROACHES 



NUCLEO-CYTOPLASMIC INTERACTION 

 IN THE OVARIAN OOCYTE 



During the long period of growth of the 

 amphibian oocyte intensive nucleo-cytoplas- 

 mic interactions must take place, as is in- 

 dicated by the profound structural changes 

 undergone by the chromosomes and the nu- 

 cleolar apparatus during this time. Recently, 

 Humphrey ('52) has found conclusive evi- 

 dence for an effect produced by an abnor- 



mal, mutated gene, the recessive lethal factor 

 for "fluid imbalance" described on page 133. 

 A single larva showing the trait and thus 

 presumably homozygous for the gene {ff) 

 survived to sexual maturity. When this sur- 

 vivor, a female, was mated to a male hetero- 

 zygous for the gene (F/), it produced off- 

 spring half of which developed the fluid 

 imbalance in a more severe form than or- 

 dinary ff embryos. Moreover, the remaining 

 offspring {Ff) developed a less severe im- 

 balance from which the majority recovered. 

 These observations can be explained most 

 easily by assuming that the ff genes of the 

 mother prodviced an effect on the cytoplasm 

 of the oocyte that expressed itself (1) in a 

 more severe condition in the ff offspring, 

 and (2) in a temporary early imbalance of 

 the Ff offspring neutralized in later develop- 

 ment by the dominant F gene brought in by 

 the sperm. 



TRANSPLANTATION OF NUCLEI 

 Extending the earlier experiments of Com- 

 mandon and de Fonbrune ('39), Lorch and 

 Danielli ('50) used the de Fonbrune micro- 

 manipulator to enucleate amoebae and to 

 transplant nuclei from one amoeba to an- 

 other. Cells with a grafted nucleus return to 

 normal activity and may divide normally. 

 If a nucleus is transferred between two dif- 

 ferent species, e.g., from A. proteus to A. 

 discoides, reactivation occurs readily while 

 nuclear and cell division are less frequent. 

 Observations on cells consisting of cytoplasm 

 of one species and nucleus of another show 

 that the form assumed by the amoeba in 

 movement is intermediate between the forms 

 typical for the two species, i.e., it is influenced 

 both by the constitution of the nucleus and 

 by that of the cytoplasm. 



More recently, Briggs and King ('52) have 

 developed a method for transplanting nuclei 

 from advanced blastvda cells into enucleated 

 eggs of the frog, R. pipiens. When the nu- 

 cleus is from the same species as the egg cyto- 

 plasm, the egg cleaves normally and can 

 develop into a normal embryo. When a nu- 

 cleus from a blastula of R. catesheiana is 

 transplanted to an enucleated egg of R. 

 pipiens, the egg cleaves but is arrested in the 

 blastula stage, as are normally produced 

 hybrids between these two species. This 

 technique of nuclear transfer from more ad- 

 vanced stages of development to the unseg- 

 mented egg shoidd prove of great value in 

 the analysis of nucleo-cytoplasmic relation- 

 ships and, particularly, of the problem of 

 nuclear differentiation dvu-ing development. 



