摘要:

AbstractThe development of the posterior axial structure of the heterozygous Brachy (T/+) mutant was studied and the expressivity and penetrance of this gene on several genetic backgrounds was analyzed.The Brachy mutant in heterozygous conditions is a dominant non‐lethal and interferes with the normal development of the caudal axis, leading to blunting, shortening and bending of the tail.Study of the developmental changes encountered in T/+ mice from the sixteenth day of gestation until the tenth day of postnatal age revealed that three different processes contribute to the tail abnormalities, these are: (1) reduction in number of tail vertebrae, (2) fragmentation of vertebral processes, (3) fusion of vertebrae or vertebral fragments.The expressivity and penetrance of the T gene in heterozygous condition was tested on four different genetic backgrounds provided by the Black Spot strain, the C57B1/6 strain, the DBA/2 strain and the Swiss Albino strain.On the DBA/2 strain, the effect of the T gene on reduction of caudal vertebrae was considerably modified when the DBA background was provided by the female parent. In reciprocal crosses of ♀T/ × ♂DBA ±, the expression of the T gene on that aspect of development was not changed. The penetrance of the T gene was, however, changed to a 2:1 ratio instead of the expected 1:1 ratio in both reciprocal crosses between T/+ heterozygotes with DBA mice.These results are interpreted as suggesting that the genetic background consists of several “factors,” each controlling independently the expression of some distinct aspect of the T gene, probably by stimulating some kind of correcting processes. The results are further interpreted to mean that some of the modifiers of T gene expressivity are probably non‐nuclear or cytoplasmic in origin, whereas the factors changing penentrance of the T gene are probably provided by more orthodox nuclear genetic loci that operate to inhibit its t

ISSN:0022-104X    

DOI:10.1002/jez.1401680202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractDorsal tail fins of tadpoles, (Rana pipiens) at various stages of metamorphosis, were cut into pieces or discs and then cultured either in Hanks balanced salt solution or Hanks containingL‐thyroxine (T4). Six concentrations of T4were tested: 3, 9, 27, 81, 250, and 750 parts per billion (ppb). In addition, early prometamorphic discs were cultured in medium containing 3 ppb of T4for different periods of time: 1, 3, 5, and 7 days and then placed into control medium for the remainder of the experimental period. Controls for this experiment were maintained continuously in either 3 ppb of T4or in control medium. To test the specificity of response to T4early prometamorphic discs were cultured in medium containing KI, DL‐thyronine orDL‐diiodothyronine. Discs respond to treatment with thyroxine by shrinkage. The degree of shrinkage was determined quantitatively by measurement of area.The results show that a direct quantitative relationship exists between concentration of thyroxine and resorption. Resorption is dependent upon the continuous presence of T4. It was also demonstrated that tail discs change in their sensitivity to thyroxine at progressive stages of metamorphosis. It is proposed that the increased sensitivity of tail tissues to T4during metamorphosis results from their previous exposure to a low but rising level of thyroid hormone that increases sharply in the donor tissues one to two days before the emergence of the forelegs. Finally, it was demonstrated that these results represent the specific action of thyroid ho

ISSN:0022-104X    

DOI:10.1002/jez.1401680203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractThe rate of mitosis in planarians was measured by two methods. First, by tabulating the proportion of nuclei displaying metaphase mitotic figures after varying lengths of time in colchicine. Second, by measuring the total DNA in a colony of planarians as a function of time. The first method gave a rate of mitosis by non‐regeneratingDugesia dorotocephalaof 1.4 × 10−4divisions/cell hour. This rate remains constant for the first 24 hours following decapitation but increases to 2.7 × 10−4divisions/cell hour by 54 hours. The rate of mitosis in the blastema was no larger than that of the mesenchymal tissues of the older portions. Measurements of the total DNA versus time gave an estimate of the average rate of cell division for spontaneously fissioning planarians of 5.8 × 10−4divisions/cell hour which, in view of the tendency of the colchicine method to underestimate the true rate, is in satisfactory agreement. The implications of these results for mechanisms of regeneration are

ISSN:0022-104X    

DOI:10.1002/jez.1401680204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractCytological and ultrastructural observations were made of normal (BALB/c) mouse morulae and embryos homozygous for thet12mutation, which is lethal at the late morula stage. Normal andt12/t12embryos are indistinguishable cytologically until the late morula stage, at which time cytoplasmic and nuclear differences become apparent. Different cells within individual normal morulae exhibit differences in cytoplasmic basophilia, and the cells appear closely applied to one another. Differences in cytoplasmic basophilia are not apparent between different cells oft12/t12morulae, and the cells appear more rounded and less closely applied. Nucleoli of normal morulae are irregular in shape, with projections which often reach the nuclear envelope, while nucleoli oft12/t12morulae exhibit extreme rounding.Nucleoli of normal embryos exhibit a net‐like nucleolonema, with fibrillar and granular elements, and several pars amorpha. Nucleoli oft12/t12morulae possess the same structural elements but the nucleolonema appears contracted. Nuclei of mutant embryos often contain several agranular electron‐dense bodies, 0.1–0.7 μ in diameter. These are infrequently observed in normal morulae. Ribosomes exist primarily in clusters in normal morulae, but large numbers of free ribosomes are observed int12/t12morulae. Many structures are common to both normal and mutant morulae, such as: fibrous strands, crystalloids, granular endoplasmic reticulum, vacuolated mitochondria, cytoplasmic vesicles, tight junctions, nuclear pores, and intranuclear annulate lamellae.Since the abnormalities exhibited byt12/t12morulae can be interpreted as degenerative changes, they do not resolve the mode of action of thetlocus or the primary cause oft12/t12let

ISSN:0022-104X    

DOI:10.1002/jez.1401680205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractCells from the kidneys of the newtDiemictylus (Triturus) viridescenswere cultured and used in experiments designed to yield information on cytokinesis. Observations and experiments were restricted to cells that were spread and flattened on the substratum. Flattened cells were capable of initiating and completing division without rounding up or disrupting their marginal attachments to the substratum. They can initiate division from a variety of geometric forms. At interphase and during division, flattened cells are under appreciable self‐induced tensile stress. Division continues when the cell is stretched between needles shortly after furrow establishment. Movement of needles between the cell and the substratum disturbed cells only when the tips of a marginal process were detached. No other connections between cell and substratum could be demonstrated. Objects stuck to the furrow surface and the stretching of attached marginal processes revealed that new surface in the furrow area is created by the stretching of pre‐existing surface. Massive cytoplasmic flow induced by micromanipulation immediately after the beginning of division and maintained throughout the process did not hamper furrowing. Division does not appear to depend upon any specific subsurface cytoplasmic arrangement in the equatorial plane and is unaffected by redistribution of the cytoplasm after the furrow is establis

ISSN:0022-104X    

DOI:10.1002/jez.1401680206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractThe role in food capture of the nematocysts on the filiform and capitate tentacles ofPennaria tiarellais discussed. The feeding response ofPennaria tiarellatoArtemiaextracts consists of cone bending and mouth opening. A similar feeding response has been demonstrated to be induced by proline at concentration as low as 10−6M. Pipecolic acid, a proline analog, also elicits a feeding response. Proline causes the head of the capitate tentacles to shrink, thereby causing the cnidocils of the large stenoteles to be prominen

ISSN:0022-104X    

DOI:10.1002/jez.1401680207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractEmbryonic animal epithelial tissue in which desmosomes are well developed has been dispersed by trypsinization and the behavior of desmosomal halves observed. An earlier report left open the question of whether desmosomes were broken down or reincorporated into the reorganized tissue. A more detailed study shows that dispersed cells, or cells which are partially separated, phagocytize half desmosomes left at the cell surface. The resulting vacuoles are angular during early stages of the process indicating that desmosomes are relatively rigid. They later become spherical and characteristic desmosomal morphology disappears. These results are discussed in connection with morphology in genetic disturbances and in development.

ISSN:0022-104X    

DOI:10.1002/jez.1401680208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractMethyltestosterone and estrone were administered orally to fry of the goldfish,Carassius auratus, daily for two months; thereafter, they were raised on a normal diet. All but one of the methyltestosterone‐treated fish developed into males, while all estrone‐treated fish developed into females. Of seven methyltestosterone‐treated males mated with normal females, six produced progeny in a 1 ♀:1 ♂ ratio and the remaining one produced only females. Of eleven estrone‐treated females mated with normal males, seven produced progeny in a 1 ♀:1 ♂ ratio and four yielded offspring in a ratio of 1 ♀ : 3 ♂. Induction of sex reversal in both directions by heterologous sex hormones was successfully accomplished. The sex ratios of the progeny of hormone‐treated goldfish provide evidence that the male

ISSN:0022-104X    

DOI:10.1002/jez.1401680209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractStarch gel electrophoretic and molecular hybridization studies indicate that the genomes of rainbow (Salmo gairdneri) and brown (S. trutta) trouts may code for eight electrophoretically distinct types of lactate dehydrogenase (LDH) subunits. The interactions of these subunitsin vivoproduce eighteen isozymes. These isozymes are naturally arranged into four groups, designateda,b,d, ande, on the basis of physico‐chemical properties. Groupsa,b, anddeach consist of five isozymes while groupeis composed of three isozymes. An obvious tissue specific distribution of the isozyme groups is observed.Like the rainbow and brown trouts, other salmonids such as the Atlantic salmon (S. salar), sockeye (Onchorynchus nerka), and bloater (Coregonus hoyi) possess numerous LDH isozymes. Also, we and others have detected an unusual multiplicity of molecular forms of other proteins inSalmonidae. Representatives of theOsmeridae,Clupeidae,Engraulidae,Argentidae, andEsocidae, which are closely related families, possess no more than five LDH isozymes. Moreover, salmonids contain twice as much DNA per cell and have karyotypes which show about twice as many chromosome arms as certain closely related forms. From these observations, it has been concluded that salmonids are tetraploids. In our view, it seems most likely that they arose through allotetraploidization of a primitive hybrid ancesto

ISSN:0022-104X    

DOI:10.1002/jez.1401680210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY

摘要:

AbstractChick embryo explants of 11 to 13 somites were cultured on various sources of protein in an attempt to determine if these proteins could relace the proteins of egg yolk as a nutrient substrate for the developing embryo. Various approaches were employed to provide a favorable low molecular weight supplement to the non‐yolk sources of protein. After 48 hours of cultivation, the protein nitrogen and DNA contents of the embryo and the extraembryonic membrane were determined and the stages of morphological development were estimated. The growth and development of embryos cultured on yolk or a mixture of yolk and white were not surpassed with the other sources of protein tested. However, a mixture of horse serum and ovalbumin which first had been equilibrated across a cellophane membrane with an homogenate of whole egg supported levels of embryo growth and development which closely approximated that achieved with yolk and white. Individually, serum supported the growth and development of the extraembryonic membrane while ovalbumin supported the embryo proper. The response of embryo explants to sera derived from laying hens, roosters, or rabbits was similar to that observed with horse serum. The growth of embryos provided with ovalbumin as the sole source of nitrogenous precursors was approximately double that previously achieved with a chemically defined medium containing a mixture of amino acids. Limited growth and development of embryo explants was observed with milk, casein, colostrum, and subblastodermic fluid. Bovine serum albumin and chick embryo extract failed to support embryo explant

ISSN:0022-104X    

DOI:10.1002/jez.1401680211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1968

数据来源: WILEY