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Melanocytes originate from the neural crest in vertebrates and migrate to the body surface where they differentiate into functional cells. Genes involved in melanocyte differentiation can be classified into two groups. One of them consists of the functional genes that control proteins specific to the function of the melanocyte. As the representative gene of this category, albino (c) locus in the mouse is considered to control tyrosinase, the key enzyme in melanogenesis. cDNA for mouse tyrosinase has been cloned and sequenced. The cDNA can be used to detect tyrosinase mRNA synthesized during melanocyte differentiation. On the other hand, genes such as brown (b) or pink-eyed dilution (p) have been assumed to control melanosome proteins. The other category consists of genes that regulate the expression of these functional genes directly or indirectly. In the mouse, so-called white-spotting genes and genes of the agouti series are considered to fall into this category. Based on the fact that mutations at the white-spotting loci result in the absence of melanocytes in a particular area of skin, it is assumed that some of these loci control the factors that promote either differentiation or migration of melanoblasts and are candidates for the classic regulator genes Genes at the agouti (a) locus in the mouse determine the type of melanin synthesized in hair follicle melanocytes, that is eumelanin or pheomelanin. An interesting feature of this locus is that the site of gene action is not within the melanocytes but in the cells surrounding them. The results of our study indicate that the gene product of the a-locus interacts with α-MSH at the α-MSH receptor site, regulates the cellular cAMP level via a signal transduction system and, in turn, determines the type of melanin synthesized in the cells. 相似文献
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SHIGEKO SUZUKI-MORIMOTO YOSHIHIRO YAMAMOTO TAKEO YAMAGUCHI 《Development, growth & differentiation》1985,27(6):729-736
Hydrocortisone is regarded as an initiator of keratinization in embryonic skin. The present investigation dealt with the effect of hydrocortisone on the proliferation of epidermal cells during early development: Cell kinetic analyses using 3 H-thymidine autoradiography were applied to a skin organ culture prepared from a 13-day chick embryo.
Hydrocortisone at a concentration between 0.01 and 1.0 μg/ml was effective in initiating a morphological change leading to the epidermal keratinization in vitro and caused a marked decrease in the mitotic and labeling indices of epidermal basal cells, the decrease being maximum at 2 days of culture previous to the morphological change.
During continuous labeling with3 H-thymidine, the number of labeled basal cells reached 100% within 2 days in the control and 4 days in the culture treated with hydrocortisone. This confirmed that the growth fraction of epidermal basal cells was 1.0 even after the administration of hydrocortisone.
The duration of each cell cycle phase at 2 days of culture was determined by percent labeled mitoses and double-labeling analyses. It was concluded that hydrocortisone extended the generation time of epidermal basal cells at this time point about three fold over the control. This extension was mainly due to the elongation of the G1 phase. 相似文献
Hydrocortisone at a concentration between 0.01 and 1.0 μg/ml was effective in initiating a morphological change leading to the epidermal keratinization in vitro and caused a marked decrease in the mitotic and labeling indices of epidermal basal cells, the decrease being maximum at 2 days of culture previous to the morphological change.
During continuous labeling with
The duration of each cell cycle phase at 2 days of culture was determined by percent labeled mitoses and double-labeling analyses. It was concluded that hydrocortisone extended the generation time of epidermal basal cells at this time point about three fold over the control. This extension was mainly due to the elongation of the G
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Macrophage Migration Inhibition by Serum from Desensitized Animals Previously Sensitized with Tubercle Bacilli 总被引:4,自引:0,他引:4
MIGRATION of peritoneal exudate cells removed from guinea-pigs or mice exhibiting delayed hypersensitivity is inhibited by specific antigen1–3. This in vitro macrophage migration inhibition has been regarded as a useful immunological test for delayed skin hypersensitivity4,5. Studies of the mechanism of this phenomenon revealed that, in contact with specific antigen, lymphocytes from sensitized animals released into the medium a specific substance (migration inhibitory factor; MIF) capable of inhibiting the migration of normal macrophages6,7. When injected intradermally into normal guinea-pigs, MIF elicits inflammatory reactions characterized by induration, erythema and mononuclear cell infiltration8. 相似文献
5.
Recruitment Processes and Species Coexistence in a Sub-boreal Forest in Northern Japan 总被引:2,自引:0,他引:2
We investigated the recruitment of saplings (across the 2 m-heightthreshold) of six species,Picea jezoensis, Abies sachalinensis,Betula ermanii, Picea glehnii, Acer ukurunduense andSorbus commixta,in a sub-boreal forest, northern Japan. Data were collectedin a 2.48-ha plot over six growing seasons (19891994).We used path analysis to analyse the relationships between therecruitment rates of saplings and the stand structural attributessuch as mother tree abundance, stand crowdedness, stand stratification,Sasabamboo density on the forest floor, and fallen log abundance.The combination of stand structural attributes affecting recruitmentrates of the six sub-boreal forest tree species differed markedlyamong the species and corresponded to species composition. Itis suggested that the size-structure dynamics of adult treesof the sub-boreal forest are regulated largely by differentregeneration processes among the species and only slightly byinterspecific competition between adult trees because interspecificcompetition between adult trees was not evident. The dynamicsof species coexistence of the sub-boreal forest should be describedas a process combining the diversity of recruitment processesof saplings of the component species and the diversity of interspecificcompetition between adult trees. We propose the boundary conditionhypothesis for species coexistence in the sub-boreal forest,that the persistence of each component species is ascribed largelyto the different recruitment processes of saplings (boundaryconditions for adult tree growth dynamics) and only a littleto interspecific adult tree competition. Climax forest; safe site; regeneration niche; mode of competition; species diversity 相似文献
6.
Artificial induction of functional sex-reversal in genotypic females of the medaka (Oryzias latipes) 总被引:8,自引:0,他引:8
YAMAMOTO T 《The Journal of experimental zoology》1958,137(2):227-263
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NORIKO KAWAMOTO YAMAMOTO 《Development, growth & differentiation》1975,17(3):253-263
The effects of hypophysectomy on spermatogenesis in testes implanted to neuter individuals of the medaka, oryzias latipes , have been histologically studied.
The neuter fish produced by prolonged androgen treatment during larval life maintained the implanted testes for more than 8 months, irrespective of the genetic sex of the host. Histological examination revealed that all the implanted testes were filled with numerous cysts containing cells at all spermatogenetic stages, as in the normal testes. Each cyst contained only cells at the same stage. Furthermore, the implanted testes had fertile spermatozoa. In the experiment of regeneration of amputated anal fins, the implanted testes were found to be able to induce the formation of papillar processes, although the number of processes was one-half of that induced by normal testes.
Hypophysectomy of the fish was successfully achieved by orbital approach. The survival rate of the operated fish was 95% a week after the operation and still 50% 14 months later. Hypophysectomy inhibited the transformation of spermatogonia to spermatocytes in spermatogenesis.
The presence of the capacity to carry out normal spermatogenesis and induce papillar processes in the testis-implanted neuter fish suggests that the hypothalamus of the neuter fish was not seriously affected by prolonged androgen treatment. 相似文献
The neuter fish produced by prolonged androgen treatment during larval life maintained the implanted testes for more than 8 months, irrespective of the genetic sex of the host. Histological examination revealed that all the implanted testes were filled with numerous cysts containing cells at all spermatogenetic stages, as in the normal testes. Each cyst contained only cells at the same stage. Furthermore, the implanted testes had fertile spermatozoa. In the experiment of regeneration of amputated anal fins, the implanted testes were found to be able to induce the formation of papillar processes, although the number of processes was one-half of that induced by normal testes.
Hypophysectomy of the fish was successfully achieved by orbital approach. The survival rate of the operated fish was 95% a week after the operation and still 50% 14 months later. Hypophysectomy inhibited the transformation of spermatogonia to spermatocytes in spermatogenesis.
The presence of the capacity to carry out normal spermatogenesis and induce papillar processes in the testis-implanted neuter fish suggests that the hypothalamus of the neuter fish was not seriously affected by prolonged androgen treatment. 相似文献