Animal Physiology and Development Insects 3 JCS Lecture

Animal Physiology and Development Insects 3 JCS Lecture

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 - 2 Bisecting embryos and culture

Evidence for determination of the blastoderm - 3 Evidence that pole plasm determines pole cells Actual genotype: +/+ (P = wild-type) e mwh (Y = ebony body, mult. wing-hair)

y w sn3 (G = yellow body, white eyes, singed bristles) 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) Maternal RNA and protein gradients 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 Gap gene - mutants Hatched areas = deletions

Stippled replacement strcutures Gap gene - expression How maternal product gradients specify gap gene expression TA 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 type Antp Bithorax homeotic mutant transformation Bithorax, Bx Homeotic / segment specification genes

ANT-C and BX-C gene complexes (HOX genes) Segmentation and insect development Segment positions on the blastoderm fate-map

Segments form in embryo (germ band extension) Dorsal closure (germ band retraction) Adult segment pattern embryonic

pattern is retained Conservation of homoetic gene expression in other arthropods

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