Animal Physiology and Development Insects –3 JCS Lecture Outcome: By the end of this lecture student should have: a)Become aware of the early processes in insect embryogenesis following fertilisation b)Understood the evidence for maternal information in the specification of the blastoderm c)Appreciated the roles of this information in producing the ant.- post. axis of the embryo d)Seen how this information leads to the segmentation of the embryo and the overall specification of the insect body plan. JCS 6/11/02

Early embryogenesis in Drosophila

Long and short germband embryos Short Long Semi-long From Wolpert ‘Principles of development

Evidence for determination of the blastoderm -1 Fate map UV-irradiation

Evidence for determination of the blastoderm - 2Bisecting embryos and culture

Actual genotype: +/+ (P = wild-type) e mwh (Y = ebony body, mult. wing-hair) y w sn 3 (G = yellow body, white eyes, singed bristles) Evidence that pole plasm determines pole cells Evidence for determination of the blastoderm - 3

Early effect female sterile mutations Major developmental question: What is put into the egg by way of information for development ? i.e what is the maternal contribution to the egg ? _________________________________________ One way to look is to search for female-sterile (fs) mutations which arrest normal development at the earliest possible stages with major effects on development. Christiana Nusslein-Volhard and Eric Wieschaus – Nobel Winners in 1995! Cross to show a recessive female sterile mutation (fs) + / fs female X + / fs male  + / + + / fs fs / fs (fs/fs are female sterile but for many different reasons; some – e.g. bicoid, nanos, oskar, torso - produce eggs which develop with major aberrations of the embryonic body plan)

Early body plan maternal effect mutants Wild type bicoid

Rescue of bicoid and oskar by cytoplasmic transplantation. (oskar is a gene which interacts with nanos, (nos) to form the posterior determinant)

bicoid RNA is localised/fixed to the ant. pole. bicoid protein diffuses to form a gradient. bcd = bicoid hb = hunchback hunchback RNA is through out the egg; nanos RNA is localised to post. pole; nanos protein diffuses and represses hunchback protein synth. creating two gradients. nos = nanos Maternal RNA and protein gradients

Gap gene - mutantsGap gene - expression Hatched areas = deletions Stippled replacement strcutures

How maternal product gradients specify gap gene expression T¦A shows how gradient specifies thorax/abdomen boundary

Examples of gap, pair-rule and segment polarity mutants

Control of hairy (h) - a pair rule gene - expression by Kruppel and knirps (gap genes).

Expression patterns and/or domains of action of the various maternal, gap and pair rule genes md: mandibular segment; ma: maxillary segment; la: labial segment; proct: proctodeum

Expression of Kruppel (gap) and hairy (pair-rule) genes in long and short germ band insects

Antennapedia homeotic mutant transformation Wild typeAntp Bithorax, Bx Bithorax homeotic mutant transformation

Homeotic / segment specification genes ANT-C and BX-C gene complexes (HOX genes)

Segments form in embryo (germ band extension) Segmentation and insect development Segment positions on the blastoderm fate-map Dorsal closure (germ band retraction) Adult segment pattern – embryonic pattern is retained

Conservation of homoetic gene expression in other arthropods