DROSOPHILA DEVELOPMENT

Embryonic development:Fertilization….Day 1: development ,embryo hatches out of the egg shell to become a larva

Day 2,03 and so : larva- three stages/instars, separated by moltingend of third stage, Pupa forms.

Inside a pupa a radical remodeling of the body - a process called metamorphosis

After Day 9:Adult fly/ Imago

Egg- series of nuclear division (every 8 minute) without cell devision creates a Syncytium

1st 9 divisions – cloud of nuclei is formed- from middle to surface of egg moment- form monolayer called Syncytial blastoderm 4 nuclear divisions

Few nuclei to extreme posterior end – few cycles (9)- pole cells- give rise to germ cells.

When the nuclei reach the periphery of the egg during the tenth cleavage cycle, each nucleus becomes surrounded by microtubules and microfilaments. The nuclei and their associated cytoplasmic islands are called energids. (up to 12th cycle)

Plasma membrane grow inward converting syncytial blastoderm into cellular blastoderm (13th cycle)

Cell division slows down, asynchronous, and transcription rate is increased.

Blastoderm fate map:

Transcription from the nuclei (which begins around the eleventh cycle) is greatly enhanced at this stage. This slowdown of nuclear division and the concomitant increase in RNA transcription is often referred to as the mid blastula transition.

Gastrulation: The first movements of Drosophila gastrulation segregate the presumptive mesoderm, endoderm, and ectoderm. The prospective mesoderm about 1000 cells constituting the ventral midline of the embryo folds inward to produce the ventral furrow. This furrow eventually pinches off from the surface to become a ventral tube within the embryo. It then flattens to form a layer of mesodermal tissue beneath the ventral ectoderm. 2:50 h

3:40 h

4:20 h

The prospective endoderm invaginates as two pockets at the anterior and posterior ends of the ventral furrow. The pole cells are internalized along with the endoderm. At this time, the embryo bends to form the cephalic furrow.

The ectodermal cells on the surface and the mesoderm undergo convergence and extension, migrating toward the ventral midline to form the germ band, a collection of cells along the ventral midline that includes all the cells that will form the trunk of the embryo.

The germ band extends posteriorly and, perhaps because of the egg case, wraps around the top (dorsal) surface of the embryo

While the germ band is in its extended position, several key morphogenetic processes occur: organogenesis, segmentation, and the segregation of the imaginal discs. Imaginal discs are those cells set aside to produce the adult structures.

In addition, the nervous system forms from two regions of ventral ectoderm. Neuroblasts differentiate from this neurogenic ectoderm within each segment (and also from the Non segmented region of the head ectoderm). Therefore, in insects like Drosophila, the nervous system is located ventrally.

Body plan of Drosophila:

HeadThree thoracic segments (T1 T2 T3)Eight abdominal segments (A1 to A8)

The first thoracic segment, has only legs; the second thoracic segment has legs and wings; and the third thoracic segment has legs and halteres (balancers).

The anterior-posterior and dorsal-ventral axes of Drosophila form at right angles to one another, and they are both determined by the position of the oocyte within the follicle cells of the ovary.