miR-219 expression in the zebrafish brain.
miR-219 is expressed in both periventricular and differentiated cells in the larval brain and has more restricted expression in differentiating cells compared to miR-124. Transcripts are localized in periventricular and adjacent cells only in few cases. miR-219 shows pronounced changes between larval and adult brain expression patterns. miR-219 transcript localization suggests downregulation of expression during maturity and conserved or de novo expression in distinct cells, possibly glia.
In the 5dpf larval brain, miR-219 is expressed in the entire ventral and dorsal thalamus, tegmentum, isthmus, medulla oblongata and ventral hindbrain areas such as the reticular formation. In addition, it is expressed in most pretectal cells, in a few pallial, ventral habenular, dorsal posterior tubercular, tectal and lateral cerebellar plate cells. It is absent from the caudal preoptic area, hypothalamus, retina and Mauthner cells (Table B). In the adult brain, it is widely expressed only in the caudal hindbrain. In the rostral adult brain, expression is often downregulated as is the case in the ventral thalamus and is limited to few distinct cells found in areas that are positive (pallium, epithalamus, central posterior (dorsal) thalamic nucleus, posterior tuberculum, pretectum, tectum, tegmentum, cerebellum) or negative in the larval brain (olfactory bulb, subpallium, caudal preoptic area, hypothalamus). In some cases these distinct adult cells, possibly glia, are associated with nerves or tracts such as the lateral olfactory tract, optic tract or commissures such as anterior, postoptic and tectal commissure, whereas the equivalent pathways in larvae are devoid of staining (Table G). A. transverse section through the larval caudal telencephalon and rostral diencephalon showing miR-219 weakly expressing cells in the rostral preoptic area (Po), eminentia thalami (ET), pallium (P), dorsal thalamus (DT) and habenula (Ha).
B. transverse section through the larval diencephalon and optic tectum showing miR-219 expressing cells in the ventral (VT) and dorsal (DT) thalamus and pretectum (Pr).
C. transverse section through the larval diencephalon and optic tectum showing miR-219 expressing cells in the dorsal periventricular posterior tuberculum (PTd), dorsal thalamus (DT) and pretectum (Pr).
D. transverse section through the larval hypothalamus, caudal midbrain and isthmus showing miR-219 expressing cells in the semicircular torus (TS), isthmic area (Is) and optic tectum (TeO).
E. transverse section through the caudal larval midbrain and isthmus showing miR-219 expressing cells in the semicircular torus (TS), isthmic area (Is), isthmic nucleus (NI), superior raphe (SR), superior reticular formation (SRF) and lateral cerebellar plate (CeP, arrowhead).
F. transverse section through the larval hindbrain at the level of the octaval ganglion showing miR-219 expressing cells in the medulla oblongata (MO), presumptive octaval area (OA) and intermediate reticular formation (IMRF). The Mauthner cell (MAC) is devoid of expression.
G. transverse section through the adult telencephalon at the level of the anterior commissure showing miR-219 expressing cells (arrows) scattered throughout telencephalic areas [Vs-supracommissural nucleus of the ventral (subpallial) telencephalic area, Dm-medial, Dc-central, Dl-lateral, Dp-posterior zones of the dorsal (pallial) telencephalic area, ac-anterior commissure].
H. higher magnification of G showing miR-219 expressing cells (arrows) scattered throughout telencephalic areas [Dm-medial, Dc-central, Dl-lateral, Dp-posterior zones of the dorsal (pallial) telencephalic area].
I. transverse section through the adult diencephalon at the level of the postoptic commissure (poc) showing miR-219 expressing cells in the poc and the optic tract (OT), the pretectal central (CPN) and superficial parvocellular (PSp) nuclei and the posterior preoptic parvocellular nucleus (PPp, arrow).
J. transverse section through the adult diencephalon and optic tectum showing miR-219 expressing cells scattered in the ventral zone of the hypothalamus (Hv), the ventral optic tract (VOT) and the tectal superficial gray zone (sgz).
K. transverse section through the optic tectum (caudal to section J) showing miR-219 expressing cells in the tectal commissure, periventricular (pgz) and superficial (sgz) gray zones and longitudinal torus (TL).
L. transverse section showing miR-219 expressing cells (arrows) scattered throughout the cerebellum (CCe) and granular eminence (EG).
M. transverse section through the adult ventral hindbrain showing miR-219 expressing cells scattered in the anterior octaval area (AON), intermediate reticular formation (IMRF) and in proximity to medial longitudinal fascicle (MLF). The areas dorsal to and the Mauthner cell (MAC) are devoid of expression.
N. transverse section through the adult ventral hindbrain showing miR-219 expressing cells scattered in the intermediate reticular formation (IMRF), anterior lateral line nerve (ALLN), octaval nerve (VIII) and in proximity to medial longitudinal fascicle (MLF) and rostral part of the abducens nucleus (NVIr). The areas dorsal to IMRF are devoid of expression.
O. transverse section through the adult caudal hindbrain showing miR-219 expressing cells throughout this area, in particular in the vagal lobe (LX), medial funicular nucleus (MFN), inferior reticular formation (IRF) and in proximity to tracts such as the bulbospinal tract (TBS) and the MLF.
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