![]() ![]() These factors were expressed in the silk gland with distinct temporal- and spatial-specificities during late larval development as well as during embryogenesis, and did not correlate directly with fibroin gene expression. Two of them (FMBP-2 and -3) were identified as a Fork head homologue (Bm Fkh) and a POU-domain protein (POU-M1) respectively. Three major FMBPs in the silk gland were characterized. The transcriptional modulator in the fibroin gene intron is composed of multiple octamer-like AT-rich elements, to which several specific DNA-binding proteins named fibroin-modulator-binding proteins (FMBPs) bind. A generalized concept of parthenogenetic engineering is proposed in the field of experimental cytogenetics dealing with the oocyte and producing new biological forms. In the last case deactivated eggs were shown capable for normal fertilization. ![]() inside live moths at the temperatures below 43☌. Deactivation and reactivation can be repeated and even performed in vivoand in situ,i.e. If cooling is quick enough (between 40☌ and 0☌) these “non-activating” temperatures can effectively activate the egg. Gradual cooling of the egg (from temperatures above 40☌) soon after its artificial or natural activation produces deactivating effect, which, in a definite sense, brings the egg back to the point before activation, from where it can be reactivated in different ways. The molecular analysis of these factors and their genetic basis could be considered not only as solving the problem of parthenogenesis but also would give us new opportunities in controlling the earliest stages of individual development. The latter can be increased through homozygotization up to 23% hatching and we can soon expect disclosure of the factors causing egg activation in the process of egg laying, which, in turn, might obliterate the “principal” differences between spontaneous (natural) and artificial types of parthenogenesis. Parthenoclones and “self-fertilization” were used in the study of ability for spontaneous parthenogenesis. This homozygotization may sometimes result in decreasing of the ability for thermoparthenogenesis that can be compensated with ovary transplantation from homozygous donor into record heterozygotic parthenoclones. This “contamination” with unknown genetic material can be excluded: ameiotic and meiotic types of parthenogenesis allow abovementioned corrections through “self-fertilization” and reversion of tetraploid eggs persisting in any clone to diploid level. Corrections of the genotype through gene or chromosome recombinations and homozygotization appear impossible unless outcrossing is used and new genetic material inevitably replaces some regions in the cloned genotype. ![]() By definition, cloning is closed genetic system of one genotype. These changes in egg microarchitecture induced by the heat shock were shown to be reversible unless fixed with abrupt cooling following the shock. ![]() Heat shock treatment at thermoactivation is supposed to trigger off egg activation processes, simultaneously destroying modified synaptonemal complexes between homologues and the spindle fibers destined to perform the reductional division. Maternal genotype of diploid female pronucleus as the basis for cloning is the result of the first meiotic division suppression and absence of crossingover in females. Reinvestigated cytological mechanism of ameiotic thermoparthenogenesis proved to be in good correspondence with Astaurov original scheme based on his genetic data. The silkworm Bombyx mori L., a unique biological system with several ways of artificial reproduction was used in experimental analysis of some problems and prospects in parthenogenesis and cloning. The University of Tokyo, Laboratory of Insect Genetics and Bioscience, Japan Parthenogenesis and Cloning in the Silkworm Bombyx mori L.: Problems and Prospects Journal of Insect Biotechnology and Sericology 70, 155-165 (2001) Review ![]()
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