let-7b expression in the zebrafish brain.
let-7a, let-7b and let-7c are expressed in both proliferating and differentiating cells. let-7b and let-7c differ in their sequence in only one nucleotide located outside the seed region. They share similar regional expression in the larval brain with two differences: let-7b is expressed in the retinal ciliary marginal zone and pineal cells whereas let-7a and let-7c are absent (table A). let-7a, let-7b and let-7c mainly conserve their regional expression between larval and adult brain (tables A, F).
let-7a, let-7b and let-7c are expressed in many proliferating and differentiating cells of the larval fore-, mid- and hindbrain with the exception of some areas such as hypothalamic nuclei (caudal hypothalamus, diffuse nucleus of inferior lobe, lateral torus) interpeduncular nucleus, locus coereleus, raphe and reticular formation. We detected only minor differences at the regional level between larval and adult brain expression. For example, let-7b and let-7c are expressed in some adult but not larval hypothalamic lateral torus and superior raphe cells (tables A, F). A. transverse section through the larval rostral telencephalon showing let-7b expressing cells in the olfactory bulb (OB).
B. transverse section through the larval telencephalon showing let-7b expressing cells in the ventral (Sv) and dorsal (Sd) subpallium and pallium (P).
C. transverse section through the larval rostral diencephalon showing let-7b expressing cells in the preoptic area (Po), eminentia thalami (ET), migrated eminentia thalami (M3), pallium (P), habenula (Ha) and epiphysis (E).
D. transverse section through the larval diencephalon and rostral optic tectum showing let-7b expressing cells in the preoptic area (Po), eminentia thalami (ET), migrated eminentia thalami (M3), ventral thalamus (VT), dorsal thalamus (DT), and optic tectum (TeO).
E. transverse section through the larval retina (dorsal to the right) showing let-7b expressing cells in the ciliary marginal zone (CMZ).
F. transverse section through the larval diencephalon and midbrain showing mainly periventricular (arrowheads) let-7b expressing cells in the dorsal (PTd) and ventral (PTv) periventricular and lateral migrated (M2) posterior tuberculum, tegmentum (T), semicircular torus (TS), longitudinal torus (TL), tectal proliferative (m) and periventricular gray (pgz) zones.
G. transverse section through the larval caudal midbrain and rostral hindbrain showing let-7b expressing cells in the semicircular torus (TS), optic tectum (TeO), isthmic/medulla oblongata area (Is/MO) and cerebellar plate (CeP).
H. transverse section through the larval rostral hindbrain showing let-7b expressing cells in the semicircular torus (TS), cerebellar plate (CeP) and isthmic/medulla oblongata area (Is/MO).
I. transverse section through the larval hindbrain at the level of the otic capsule showing let-7b expressing cells in the medulla oblongata (MO) and rhombic lip (RL).
J. transverse section through the adult rostral telencephalon showing let-7b expressing cells in the dorsal telencephalon/pallium (P) and olfactory bulb (OB).
K. transverse section through the adult caudal hindbrain showing let-7b expressing cells in the inferior reticular formation (IRF), posterior octaval (PON) and caudal octavolateral (CON) areas, facial lobe (LVII) and around the rhomboncephalic ventricle (arrowhead).
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