Interaction of mutant genes Fgf5go-Y, we, and wal changes the duration of hair growth cycles in mice

Mutant gene wallhaarig (wa) was acting as a modifier of the mutant gene waved alopecia (wal), substantially increasing hair loss rate in mice, as was previously shown in our laboratory. The current paper is devoted to a study of mutant gene angora-Y (Fgf5 ^go-Y ), which had extended anagen stage of the first and second generations hair growth cycles in triple heterozygotes (Fgf5 ^go-Y /Fgf5 ^go-Y we/we wal/wal). First generation guard hair in triple homozygotes had their anagen stage 4 days longer than the same stage in double homozygotes (+/+ we/we wal/wal). Hair loss started at a catagen stage in double homozygotes, while it started in triple homozygotes at the end of the same stage or even in a telogen. Such mutant gene interaction in hair follicle morphogenesis led to a partial recovery of a body hair coat in triple homozygotes.     

The we gene is a modifier of the wal gene in mice

Interaction of gene wellhaarig (we) with genes waved alopecia (wal) and hairless (hr) was studied in mice. The mutant gene we is responsible for the development of a specific waved coat in homozygotes. Homozygous mice carrying mutant gene wal also have a wavy coat, though a partial alopecia develops with time in these animals. In homozygotes for the hr gene, hair loss is observed beginning from the age of ten days. A series of crosses we/we and wal/wal yielded animals with we/+wal/wal and we/we wal/wal genotypes. In mice we/+wal/wal carrying gene we at a single dose, alopecia is accelerated significantly as compared to the single-dose homozygotes +/+wal/wal. In we/we wal/wal mice, alopecia starts earlier than in we/+wal/wal mice; by the age of one month, the double homozygotes are almost hairless except for small body areas covered with a sparse coat. In addition, curliness of the first-generation hair in mice we/we wal/wal is much more expressed than in +/+wal/wal and we/we+/+ mice. The obtained evidence suggests that the we gene is a modifier of the wal gene because the former enhances the effects of the wal gene, which is confirmed by the earlier onset of alopecia and progression of the latter in mice having the we/+wal/wal genotype and especially in we/we wal/wal animals. The we/we hr/+ mice do not differ in coat from we/we+/+ mice; in both cases, the coat is wavy. The coat of double homozygotes we/we hr/hr, is similar to that of we/we+/+ mice until ten days of age, when the signs of alopecia appear. By the age of 21 days, mice we/we hr/hr have lost their coat completely like mice +/+ hr/hr. Hence, the we gene is a modifier of the wal gene though it does not interact with hr gene during the coat formation.     

两例新的稀毛小鼠突变基因的染色体定位

用连锁分析法对乙烷基亚硝基脲(ENU) 诱变获得的两例被毛突变小鼠(snthr 1Bao及snthr 2Bao) 的突变基因进行定位。选择平均分布于小鼠基因组且在C57BL/6J和DBA/2 间有差异的39 个微卫星对B6D2F1 互交得到的稀毛F2 进行全基因组扫描。扫描了9个微卫星后发现snthr 1Bao突变基因与D9Mit243 的LOD值为7 73。突变基因被定位于9号染色体。在此基础上又选择了D9Mit355 和D9Mit18 两个微卫星进行检测, 并扩大F2 的数量至145只。结果发现, snthr 1Bao与D9Mit18间无1 例重组, 稀毛突变基因与该微卫星紧密连锁, 距着丝点71cM。同理, 将snthr 2Bao突变基因也定位在与snthr 1Bao相近的区域。检索发现snthr 1Bao是一尚未克隆的新基因。     

Cryopreservation of strains and mutant genes in mice

Three kinds of freezing methods were tested with embryos of DNI strain. The survival rate after thawing was 47.5%, 66.7% and 77.8% in the 2-step method, modified slow freezing method and modified 2-step method, respectively. Then, the modified 2-step method was applied to the embryos from 7 strains and a pair of interstrain crosses. PMSG treatment at the beginning of diestrus following HCG treatment after 48 hrs resulted in much yield of 8-16-cell embryos in all strains. The average number for each strain was as follows: DNI; 18.9, DDN; 13.0, BS; 20.4, C57BL/6; 12.9, DBA/2; 17.5, CRN; 19.8, PAN; 13.7 and DNI x C57BL/6-Ay; 21.7. Development of frozen-thawed embryos in culture varied among strains. Proportion of embryos that developed to the morula or blastocyst stage was as follows: DNI; 64.6%, DDN; 71.9%, BS; 53.6%, C57BL/6; 57.3%, DBA/2; 65.0%, CRN; 52.5%, PAN; 17.4% and DNI x C57BL/6-Ay; 44.1%. These results indicate that the ability of embryos to survive freezing and thawing is influenced by their genetic background. Live young were produced from DNI, DDN, BS and DNI x C57BL/6-Ay embryos after transfer to recipients. Comparative assessment of the developmental ability of frozen-thawed embryos after transfer among strains should be performed in further study.     

The interaction of the coloboma and aphakia mutant genes in mice

The eye development has been studied in the 12-day-old, 14-day-old embryos and in neonates of Cm/+ ak/ak genotype. The gene coloboma (Cm) in heterozygous state causes a typical coloboma of the iris and the gene aphakia (ak) blocks the lens development in the homozygotes. It has been shown that in Cm/+ ak/ak mice the eyes go through mainly the same abnormal development as that in +/+ ak/ak animals. In mice of both genotypes the lens morphogenesis blocking at the vesicle stage and the retinal fold in the dorsal half of the eye develops. However, the ventral retinal fold which is characteristic for the +/+ ak/ak mice does not form in the Cm/+ ak/ak animals that is the result of the interaction of Cm and ak genes in the eye morphogenesis. The Cm gene suppressing the growth of the retina ventral half inhibits the formation of its fold in Cm/+ ak/ak embryos. As a result of the gene interaction a certain normalization of the eye development compared to the +/+ ak/ak mice is observed in the Cm/+ ak/ak animals. The obtained data show that the Cm gene expresses in the cell clones of the retina ventral half.     

Analysis of the effects of mutant hairless genes in chimeric mice

The autosomal recessive gene hairless (hr) is responsible for the complete hairlessness in mice homozygous for this gene. Hair shedding that begins at the age of 10 days is caused by an abnormal cycle of hair follicle development disturbed at the catagen stage. This results in enhanced programmed cell death (apoptosis) and ultimately leads to the complete hair follicle destruction and shedding of all hairs by the age of three weeks. To study the phenotypic expression of the hr gene in a chimeric organism, we have obtained 12 chimeric mice hr/hr <--> +/+ by means of aggregation of early embryos hr/hr and +/+. In chimeric mice, the hair shedding has begun two days later than in the hr/hr mice. By day 23 of postnatal development, hairless areas were present on the coat of chimeric mice or the latter were completely hairless depending on the percentage of the hr/hr mutant component. In four chimeras with high content of the mutant component (68-76%), the hair shedding process was similar to that in the hr/hr mice, though it was accomplished two days later. In three chimeras with 48-51% of the mutant component, alternating hairless and hair-covered bands were observed. These data suggest that the hr gene acts in epidermal cells of a hair follicle, because epidermal cell clones in embryonic skin migrate in the lateral-ventral direction coherently and without mixing. However, some chimeras displayed a pattern which was not so clear-cut: the band borders were illegible and hairs partly covered the hairless areas. In some chimeras, the uniform thinning of the coat was observed. Analysis of the effects of the hr mutant gene in chimeric mice differing in the ratio between mutant (hr/hr) and normal (+/+) components in tissues suggests that the hr gene acts in the epidermal cells of the hair follicle. The interactions between cells have an essential effect on the mode and degree of the hr gene expression, which leads to distortion of the "ectodermal" coat pattern in chimeras.     

Expression of Fibroblast growth factor 19 (Fgf19) during chicken embryogenesis and eye development, compared with Fgf15 expression in the mouse

The normal development of eyes relies on proper signaling through Fibroblast growth factor (FGF) receptors, but the source and identity of cognate ligands have remained largely unknown. We have found that Fgf19 is expressed in the developing chicken retina. In situ hybridization discloses dynamic expression patterns for Fgf19 in the optic vesicle, lens primordia and retinal horizontal cells. Overall expression pattern of Fgf19 during chicken embryogenesis was also examined: Fgf19 is expressed in the regions associated with cranial placodes induction, boundary regions of rhombomeres, somites, specific groups of neural cells in midbrain, hindbrain, and those derived from epibranchial placodes, and the apical ectodermal ridge of limb buds. Expression pattern of the Fgf19-orthologous gene Fgf15 was further examined in the mouse developing eye. Fgf15 is expressed in the optic vesicle, a subset of progenitor cells of neural retina, and emerging ganglion and amacrine cells during retinogenesis.     

When whorls collide: the development of hair patterns in frizzled 6 mutant mice

Surface appendages such as bristles, feathers and hairs exhibit both long- and short-range order. In the frizzled 6 null (Fz6(-/-)) mouse the orientations of the earliest born hair follicles are uncorrelated, but over time the follicles reorient to create patterns that are characterized by a high degree of local order. By quantifying follicle orientations over time, in both living and fixed tissues, we define the time course of local hair follicle refinement and the resulting evolution of a montage of competing patterns in Fz6(-/-) skin. We observe an apparently local process that within one week can organize a field of many tens of thousands of follicles, generating long-range order that extends over distances of more than one centimeter. Physical systems that undergo an analogous ordering of vector components suggest potential mechanisms that might apply to the patterning of hair follicles and related biological structures.     

Molecular analysis of external genitalia formation: the role of fibroblast growth factor (Fgf) genes during genital tubercle formation

The molecular mechanisms underlying the development of the external genitalia in mammals have been very little examined. Recent gene knockout studies have suggested that the developmental processes of its anlage, the genital tubercle (GT), have much in common with those of limb buds. The Fgf genes have been postulated as regulating several downstream genes during organogenesis. Fgf8 was expressed in the distal urethral plate epithelium of the genital tubercle (GT) together with other markers such as the Msx1, Fgf10, Hoxd13 and Bmp4 expressed in the mesenchyme. To analyze the role of the FGF system during GT formation, an in vitro organ culture system was utilized. It is suggested that the distal urethral plate epithelium of GT, the Fgf8-expressing region, regulates the outgrowth of GT. Ectopic application of FGF8 beads to the murine GT induced mesenchymal gene expression, and also promoted the outgrowth of the GT. Experiments utilizing anti-FGF neutralizing antibody suggested a growth-promoting role for FGF protein(s) in GT outgrowth. In contrast, despite its vital role during limb-bud formation, Fgf10 appears not to be primarily essential for initial outgrowth of GT, as extrapolated from Fgf10(-/-) GTs. However, the abnormal external genitalia development of Fgf10(-/-) perinatal mice suggested the importance of Fgf10 in the development of the glans penis and the glans clitoridis. These results suggest that the FGF system is a key element in orchestrating GT development.