Somitigenesis, Anterior-Posterior specification

Segmentation in Vertebrates: SOMITIGENESIS

Somite oscillator: Notch signaling induced expression of Hairy-1 (in blue)

Twist Protein specifies mesoderm

Lateral inhibition in neurectoderm to specify neruogenesis: Notch mediated

Somite oscillator: Notch signaling induced expression of Hairy-1 (in blue)

Presomitic paraxial mesoderm budding off to somites: Ephrin controlled

Figure 14.7(2) Ephrin and Its Receptor Constitute a Possible Cut Site for Somite Formation

Somitigenesis determines number of segments, . . . then HOX GENES give distinct identity to each segment

Segmentation genes determine number of segments, . . . then HOM/HOX GENES give distinct identity to each segment

Fly Vertebrate

Homeotics

Figure 9.8(1) Model of Drosophila Anterior-Posterior Pattern Formation

BX-C

ANTP-C + BX-C = HOM-C homoeotic complex

Figure 9.7 Comparison of Larval and Adult Segmentation in Drosophila

Figure 9.32 Differences Between Ubx Expression in Parasegments 5 and 6

Figure 9.31 Antibody Staining of the Ultrabithorax Protein in (a) the Wing Disc and B) the Haltere Disc of Third instar Drosophila Larvae

HOM EXPRESSION, ONCE ON, PERSISTS!

Figure 9.33(1) Homeodomain-DNA Interactions

Homeotic geneHomeodomainHomeobox

Figure 9.33(2) Homeodomain-DNA Interactions

Legs

BX-C:

VERTEBRATE Homeotic complex is called HOX

Segmentation in Vertebrates Notch oscillator and FGF

Somite oscillator: Notch signaling induced expression of Hairy-1 (in blue)

Segmentation in Vertebrates

Presomitic paraxial mesoderm budding off to somites: Ephrin controlled

Segmentation in Vertebrates

Figure 14.7(2) Ephrin and Its Receptor Constitute a Possible Cut Site for Somite Formation

Segmentation in Vertebrates

Wnt3a Fgf8

Cdx1 Cdx2 Cdx4 Caudal-like genes

Figure 11.43 Deficient Development of Neural Crest-Derived Pharyngeal Archand Pouch Structures in Hoxa-3-Deficient Mice

Figure 11.44 Partial Transformation of the First Lumbar Vertebra into a ThoracicVertebra by the Knockout of the Hoxc-8 Gene

Hoxb-4

Figure 9.22(2) Conversion of Maternal Protein Gradients into Zygotic Gap Gene Expression

Not in Hoxcomplex

HOX – Evolution

Legs

BX-C:

VERTEBRATE Limb – HOX Involvement

Hoxa-11/d-11mutant

Hoxd-13mutant

Figure 23.14 Homologous Pathways Specifying Neural Ectoderm in Protostomes (Drosophila) and Deuterostomes (Xenopus)

Figure 11.45(1) The Effect of Retinoic Acid on Mouse Embryos

Figure 11.45(2) The Effect of Retinoic Acid on Mouse Embryos

Figure 9.23 Specific Promoter Regions of the even-skipped (eve) Gene Control Specific Transcription Bands in the Embryo