MATH 499 VIGRE Seminar: Mathematical Models in Developmental Biology Drosophila development 101

Fruit fly lifecycle

Beginning

Anterior-Posterior Axes Specification Maternal mRNAs a) Nurse cells deposit mRNAs into oocyte b) Bicoid mRNA localized at anterior, nanos at posterior c) Bicoid mRNA translated and forms protein gradient from anterior to posterior d) Nanos mRNA translated and forms posterior to anterior protein gradient e) Hunchback and caudal expressed uniformly Translation a) Hunchback mRNA translation suppressed in posterior by nanos b) Bicoid acts as transcription factor to activate hunchback translation c) Bicoid represses caudal translation d) Hunchback and caudaul form opposing gradients, with that of hunchback being strengthened by bicoid Gap-genes a) Gap genes are activated/repressed by maternal effect genes b) Gap genes and their products interact to sharpen expression boarders c) Embryo is diveded into unique domains Pair-rule genes a) Protein products of gap genes interact with their neighboring gap gene’s proteins to activate transcription of pair-rule genes b) Pair-rule genes expressed in seven stripes c) Defines 14 parasegments, altenating between pair-rule expression and none Segment-polarity genes a) Segment polarity genes act to define an anterior and posterior part of each parasegment

Experimental Evidence

1. Loss of gap gene results in a reduced number of segments as shown in the embryo to the right. 2. Loss of a pair rule-gene, e.g. even-skipped, allows only odd-numbered segments to develop. 3. Loss of a segment polarity-gene leads to segments with similar head and tail ends.

Even-skipped, Eve