Devo Lect 11 - Neural tube and Vision Flashcards
Main changes in differentiation in ectoderm
Macroscopic changes, tissue level changes, cellular level changes
Macroscopic
3 areas (primary vesicles): forebrain, midbrain, hindbrain; divide: forebrain (telencephalon and diencephalon, midbrain (mesencephalon0, hindbrain (metencephalon, myencephalon);
5 secondary vesicles
Telencephalon, diencephalon, mesencephalon, metencephalon, myelencephalon (most anterior to posterior)
Adult derivatives of telencephalon
Olfactory, hippocampus, cerebrum
Adult derivatives of diencephalon
Retina, epithalamus, thalamus, hypothalamus
Adult derivatives of mesencephalon
Midbrain
Adult derivatives of metencephalon
Cerebellum, pons
Adult derivatives of myencephalon
Medulla
Cells of neural tube
Ventricular zone: neural stem cells; Intermediate layer: gray matter; marginal zone: white matter. Still present in adult (with other nuclei)
Neural stem cells
We still have them as adults! But they can’t migrate or there aren’t enough to repair damage to brain
Chick-Quail chimera (brain)
Nicole le Douarin: View brain development and fate map; can be viewed under microscope
Chick-Quail crowing pattern chimera
Mesencephalon/diencephalon graph, changed crowing pattern; that part of brain is involved in that function; affects behaviour
Development of vertebrate eye
Forms after neural tube (from diencephalon); neural tube bulges out (evagination) to form optic vesicles; about day 30 in humans; optic cup (retina), epidermis invaginates to form eye pit; at day 33, pit has pinched off, will become lens, epidermis on outside will be cornea; completed around day 60 (stage 23)`
Holoprosencephaly
Abnormal outpouching of diencephalon; telencephalon and diencephalon don’t divide and hemispheres don’t separate normally; usually results in death or mental defects
Cyclopia
Diencephalon doesn’t split into two eyes;
Pax6 phenotypes
+/+: normal; +/-: small or malformed eyes; -/-: no eyes, brain development
Aniridia
Human condition, Pax6 +/-, no iris
Role of pax6
Highest in presumptive invaginating lens; not expressed in completed eye, therefore it is implicated in development of the eye
Refresher on in situe hybridization
Complementary nucleic acid probe for mRNA, fluoresces; put directly on tissues
What type of molecule is Pax6?
Transcription factor, binds to promoter regions of crystalline genes
Promoter vs enhancer
Promoter regions are close and in front of genes, turn genes on or off; enhancers are often further away, serve to amplify
Drosophila homologue to Pax6?
Eyeless, very similar to human pax6 (almost interchangeable! - ectopic experiments on flies).
Other animals with pax6?
Squid, flatworms, C. elegans, jellyfish, tunicates, many of them don’t even have eyes! Affects sense organs in anterior part of C. elegans - anterior central nervous system
Eye types
Simple eye: one lens, formed from brain and epidermis (vertebrates); Compound eye: many tiny lenses (or omatidia), almost all from epidermis (arthropods); simple: all from epidermis (cephalopod)
