RESUMEN
The components of the pupal cuticle are the main differentiation products synthesized by both the larval and adult epidermis during the prepupal period of Drosophila development. The pupal cuticle is formed in vitro by imaginal discs in response to a 6 h pulse of 20-hydroxyecdysone (20-HE). We previously described the isolation and initial characterization of four ecdysone-dependent genes (EDGs) whose expression in imaginal discs occurs only in response to a pulse of 20-HE. In this report, we demonstrate that the pattern of temporal and tissue-specific expression of these EDGs in vivo is like that expected for genes that encode pupal cuticle proteins. Transcripts of these genes are detected in prepupae only in the epidermis and only when cuticle components are synthesized and secreted. Nonetheless, their temporal and spatial patterns of accumulation differ. EDG-84A-1 transcripts accumulate only in prepupae and only in imaginal cells. EDG-78E and EDG-64CD transcripts accumulate at the same time in both larval and imaginal cells. EDG42-A transcripts appear first in prepupae in imaginal cells and then, after a 2-4 h lag, in larval cells. It is evident that some genes are not restricted in their expression to only larval or imaginal epidermis.
Asunto(s)
Diferenciación Celular , Drosophila melanogaster/embriología , Embrión no Mamífero/citología , Transcripción Genética , Animales , Ecdisterona/farmacología , Embrión no Mamífero/efectos de los fármacos , Embrión no Mamífero/fisiología , Expresión Génica/efectos de los fármacos , Hibridación in Situ , Pupa , Mapeo Restrictivo , Transcripción Genética/efectos de los fármacosRESUMEN
We describe our analysis of IMP-L2, one of a set of six ecdysone-inducible genes in imaginal discs of Drosophila whose transcripts are associated with membrane-bound polysomes. The spatial and temporal patterns of expression of the IMP-L2 transcript were analyzed. This transcript is first expressed in imaginal discs in areas that are precursors of head and thoracic epithelium, particularly the peripodial epithelia. It is later expressed in the imaginal histoblasts, precursors of the adult abdomen. The appearance of IMP-L2 transcript in each of these tissues precedes the spreading and fusion of the separate imaginal anlagen to form the continuous adult epidermis.
Asunto(s)
Drosophila/genética , Epidermis/embriología , Regulación de la Expresión Génica , Animales , Enzimas de Restricción del ADN/metabolismo , Desoxirribonucleasa EcoRI , Ecdisona/genética , Morfogénesis , Transcripción GenéticaRESUMEN
A unique set of genes that encodes hormone-inducible transcripts found on membrane-bound polysomes is expressed during ecdysone-dependent morphogenesis of Drosophila imaginal discs cultured in vitro. The pattern of expression of one of these genes, IMP-E1, was analyzed in tissues from late third instar larvae and white prepupae by hybridization of asymmetric RNA probes to tissue sections. The IMP-E1 transcript was detected in all anterior and posterior imaginal discs except the ommatidial region of the imaginal eye disc. Within the imaginal leg disc, the IMP-E1 transcript is expressed more abundantly in the proximal than in the distal portions of the epithelium. The distribution of transcripts is consistent with the hypothesis that the IMP-E1 gene product is involved in the cell rearrangements associated with morphogenesis of the disc epithelium. The IMP-E1 transcript is also expressed at pupariation in glial cell layers that ensheath the brain. This glial cell transcript is the same size (7.5 kb) and polarity as the imaginal disc transcript, and is also transcribed in response to 20-hydroxyecdysone. Similarities between the morphogenetic changes in imaginal disc and glial cell layers during metamorphosis are discussed.
Asunto(s)
Drosophila/genética , Epidermis/embriología , Regulación de la Expresión Génica , Animales , ADN/aislamiento & purificación , Células Epidérmicas , Células Epiteliales , Larva/crecimiento & desarrollo , Metamorfosis Biológica , Morfogénesis , Hibridación de Ácido Nucleico , ARN/aislamiento & purificación , ARN Mensajero/análisisRESUMEN
The organization of septate junctions during morphogenesis of imaginal disks is described from freeze-fracture replicas and thin sections with a view to understanding junction modulation during rearrangements of cells in epithelia. The septate junctions of each epithelial cell of the disk are distributed in a number of discrete domains equal to the number of neighboring cells. Individual septa traverse domains of contact between pairs of adjacent cells, turn downwards at the lateral boundary of the domain and run parallel to the intersection with a third cell. This arrangement leaves small channels at three-cell intersections that are occupied by specialized structures termed "tricellular plugs." Cell rearrangement involves a progressive change in the width of contact domains between adjacent cells, until old contacts are broken and new ones established. It is proposed that the septate junction adjusts to the changing width of domains by the compaction or extension of existing septa. This redistribution of septa theoretically allows a transepithelial barrier to be maintained during cell rearrangements. The applicability of this model to other epithelial tissues is discussed.