摘要:

AbstractSex determination in mammals is mediatedviathe supporting cell lineage in the fetal gonad. In the very early stages of gonadal development, the fate of the supporting cell population is critically dependent on the expression of the male‐determining gene on the Y chromosome. If this gene is absent or fails to be expressed, or is expressed too late or in too small a number of supporting cells, all supporting cells (XX or XY) differentiate as pre‐follicle cells and development proceeds along the female pathway. Supporting cells in which the male‐determining gene is expressed in a timely manner differentiate as pre‐Sertoli cells; given sufficient such cells, testis cords form and development proceeds in a male direction. If XX supporting cells are also present, a few may be recruited into the pre‐Sertoli population and participate in testis cord formation. The subsequent fate of pre‐follicle cells depends critically on interaction with the germ cell population in the developing gonad: absence of germ cells may lead to partial masculinization of the gonad, and/or to disappearance of the supporting cel

ISSN:0265-9247    

DOI:10.1002/bies.950130402

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

年代:1991

数据来源: WILEY

摘要:

AbstractTitin, the largest protein identified to date (over 1 μm long, almost 3 million daltons in mass) is the third most abundant component of the sarcomere. In the mature myofibril, titin molecules span from M line to Z line, forming a third filament system which provides sarcomeric alignment and elastic recoil. In the developing sarcomere, accumulating evidence from studies bothin vivoandin vitroimplicates titin as part of a morphogenetic scaffolding, upon which critical events in myofibrillogenesis are coordinated in a time‐ and spacedependent mann

ISSN:0265-9247    

DOI:10.1002/bies.950130403

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe human serum protein α1‐antitrypsin is the major source of antiprotease activity found in the blood. The protein is synthesised primarily by liver cells but, to a lesser extent, by at least one other cell type. Expression of the gene has provided a paradigm for studies on transcriptional regulation in liver and of tissue‐specific promoter activity. The pleiomorphic nature of the gene has given rise to a variety of α1‐antitrypsin variants some of which are clinically important. These abnormal variants may be poorly synthesised, rapidly degraded or inefficiently secreted; studies on the molecular mechanisms which underly these events are providing interesting insights into the general processes of protein transport and intracellular protein degr

ISSN:0265-9247    

DOI:10.1002/bies.950130404

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe shape and turnover of photoreceptor membranes appears to depend on associated actin filaments. In dipterans, the photoreceptor membrane is microvillar. It is turned over by the addition of new membrane at the bases of the microvilli and by subsequent shedding, mostly from the distal ends. Each microvillus contains actin filaments as a component of its cytoskeletal core. Two myosin I‐like proteins co‐localize with the actin filaments. It is suggested that one of the myosin I‐like proteins might be linked to the microvillar membrane. By interacting with the actin filaments, this motor should move the membrane of a microvillus in a distal direction, thus providing a possible mechanism for the turnover of the membrane.A vertebrate photoreceptor cell contains a small cluster of actin filaments in its connecting cilium at the site where new transductive disk membranes are formed. Disruption of the actin filaments perturbs disk morphogenesis. The most likely explanation for this perturbation is that the process of initiating a new disk is inhibited. Conventional myosin (myosin II) is found in the connecting cilium with the same distribution as actin. A simple model is proposed to illustrate how the actin–myosin system of the connecting cilium might function to initiate the morphogenesis of a disk m

ISSN:0265-9247    

DOI:10.1002/bies.950130405

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

年代:1991

数据来源: WILEY

摘要:

AbstractEarly development in many animals is programmed by maternally inherited messenger RNAs. Many of these mRNAs are translationally dormant in immature oocytes, but are recruited onto polysomes during meiotic maturation, fertilization, or early embryogenesis. In contrast, other mRNAs that are translated in oocytes are released from polysomes during these later stages of development. Recent studies have begun to define thecisandtranselements that regulate both translational repression and translational induction of maternal mRNA. The inhibition of translation of some mRNAs during early development is controlled by discrete sequences residing in the 3′ and 5′ untranslated regions, respectively. The translation of other RNAs is due to polyadenylation which, at least in oocytes of the frogXenopus laevis, is regulated by a U‐rich cytoplasmic polyadenylation element (CPE). Although similar, the CPE sequences of various mRNAs are sufficiently different to be bound by different proteins. Two of these proteins and their interactions are described

ISSN:0265-9247    

DOI:10.1002/bies.950130406

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

年代:1991

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950130407

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn a recent paper, Walter Gilbert's group has estimated the number of original exons from which all extant proteins might have been constructed. The approach used is subjected to a critical analysis here. It is shown that there are flawed assumptions about both the mechanism and generality of exon‐shuffling and in the sequence comparison procedures employed, the latter failing to distinguish chance similarity from similarity due to common ancestry. These methodological errors lead to the omission of many known cases of exonshuffling and the inclusion of others which may not be genuine. In consequence, the analysis from the Gilbert group cannot give a reliable estimate of those modules that actually participated in exon‐shuffling and provides no information on the number of protein archetypes that did not participate in these proces

ISSN:0265-9247    

DOI:10.1002/bies.950130408

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

年代:1991

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950130409

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

年代:1991

数据来源: WILEY

摘要:

AbstractRecent genetic manipulations have revealed that the cytoplasm of the earlyDrosophilaembryo contains localized information that specifies the future embryonic axes. It is the restricted distribution or activity of particular gene products, either messenger RNA or protein, that is crucial for this specification. While some of the genes responsible for this information have been seqenced and the nature and distribution of their products examined, it is not known how this localization is established or maintained. The actin‐based cytoskeleton is a likely candidate for the formation of a cytomatrix that would allow such distributions and yet no direct evidence has yet been found that implicates actin in positional cue localization. In this review I summarize what is known about actin filament behavior. inDrosophilaembryos and compare it to the distribution of positional cues. My purpose is to juxtapose these two bodies of information such that the relationship between them may be reveale

ISSN:0265-9247    

DOI:10.1002/bies.950130410

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

年代:1991

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950130411

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

年代:1991

数据来源: WILEY