Congress Abstracts - Society for Developmental Biology

Program/Abstract # 469
Search for novel genes involved in hindbrain segmentation
Vazquez-Echeverria, Citlali; Escarcega, David (Inst Tecnol y Estudios Superiores de Monterrey, Mexico); Pujades, Cristina (Univ
Pompeu Fabra, Spain)
In the hindbrain, anteroposterior (AP) patterning involves a segmentation process that leads to the formation of seven bulges named
rhombomeres (r). Early events leading to the segmentation of vertebrate hindbrain into rhombomeres with distinct identities are still
not well understood. Cell patterning along the AP axis has been shown to be initiated during gastrulation and subsequently refined
during neurulation. Cells are specified or committed to different rhombomere fates before morphological distinctions among them
could be discerned. This commitment is presumably accompanied by changes in gene expression. To identify new genes expressed in
specific rhombomers in mice we have explored the use of transcriptional profiling of single pre-rhombomeric cells, in the context of
hindbrain segmentation by analyzing cells when the specification of the identity of the segment is just beginning. DNA microarray
analysis was combined with single-cell PCR procedure to study gene expression profiles of single cells from different prerhombomeric
territories (pre-r4 and pre-r5). Our results showed a Rhombomeric differential gene expression for: Tbx20, HNF-3,
Wnt14b, Pbx4, Klf15, POU-III, Emx1, Olig1, Hes5, bicc1, Limk1, Crabp1. We are currently searching whether differentially
expressed genes are involved in cell decision for an specific rhombomeric identity by different bioinformatics' methods.
Program/Abstract # 470
Induction of Brn3a Through Ectopic Expression of Mash1, Ngn1, or Ptf1a
Landsberg, Rebecca L. (Coll. of St. Rose, USA); George, Angela (Springfield, USA)
The inferior olivary nucleus (ION) is involved in coordinating balance and movement by relaying inputs from the cortex and the
spinal cord to the Purkinje cells in the cerebellum. The progenitors that generate the neurons of the ION have been localized to the
caudal extent of the dorsal embryonic hindbrain neural tube inclusive of an anatomical region known as the lower rhombic lip (LRL).
Progenitors within the LRL are arranged along the dorsoventral (D/V) axis into distinct domains predictive of future cell fate. The
relative location of ION progenitors has been mapped to ventral regions of the caudal LRL that express Ptf1a, Olig3, and Wnt1. We
have data that suggests that posterior regions of the ION might arise from more dorsal pools of progenitors that express either Ngn1 or
Mash1, suggesting a much larger territory of progenitors responsible for ION production. The ION is one of the few structures in the
ventral medulla that has been shown to express the transcription factor Brn3a. We wished to determine if over- or missexpression of
Ngn1 or Mash1 in the NB2A neuroblastoma cell line would correlate with ectopic expression of Brn3a, which is expressed by ION
neurons immediately after they exit the LRL. Our studies found that cells transfected with Ngn1, Mash1, or Ptf1a consistently
exhibited increased levels of Brn3a protein while cells transfected with Math1 or vector alone did not express Brn3a. The data
suggests that Brn3a expression can be activated by Ngn1, Mash1, or Ptf1a, supporting a model in which the neurons of the ION arise
from progenitors with a history of expression Ngn1, Mash1, or Ptf1a.
Program/Abstract # 471
Determination of neural precursor cell commitment into mesencepahlic dopaminergic neurons
Guerrero, Gilda; Bastidas, Aimée; Covarrubias, Luis (UNAM-Cuernavaca, Mexico)
It is considered that cells define their fate progressively during development by going stepwise through mechanisms that restrict their
plasticity (e.g., competence, specification, commitment). Although molecular markers are good indicators of specification and
differentiation, functional assays are required to define the signals involved and the time at which cells become fully committed. In
this work, we focus in defining when neural precursor cells of the midbrain (mNPC) determine their fate into dopaminergic neurons
(mDAN). We analyzed the differentiation of ventral mNPC, the source of mDAN, from different stages after transplantation to E10.5
midbrain explants. We observed that ventral E10.5 mNPC (Lmx1a+, Ngn2+, Nurr1-, Th-) implanted in E10.5 midbrain explants
behave as committed showing differentiation into mDAN even when they differentiate out of the natural milieu around the midline. In
contrast, E9.5 mNPC from the ventral region (Lmx1a+, Ngn2-, Nurr1-, Th-) differentiate into TH+ neurons only when implanted
around the midline. Re-specification of mNPCs failing to differentiate into mDAN out of the midline did not occur since they retained
Lmx1a expression. Lmx1a+ rosette-like structures were commonly found in explants when donor mNPCs were from E9.5 but not
from E10.5 embryos, and thus, appear to be a characteristic of the non-committed mNPC developmental stage (Dev.Biol. 349, 192-
203, 2011). Despite this association, we propose that E9.5 mNPC are competent to differentiate into mDAN but, due to the lack of
signals needed for specific differentiation (e.g., Shh, Fgf), the apparent un-committed phenotype was observed.
Program/Abstract # 472
Loss of Dll1 affects the timing of neurogenesis in the midbrain dopaminergic niche
Valencia, Concepción; Trujillo-Paredes, Niurka; Guerrero, Gilda (UNAM-Cuernavaca, Mexico); Guerra-Crespo, Magdalena
(UNAM-México city, Mexico); Baizabal, José Manuel; Covarrubias, Luis (UNAM-Cuernavaca, Mexico)
Notch signaling is a well-established pathway that regulates neurogenesis during vertebrate nervous system development. However,
little is known about its role in the differentiation of specific neuron types. In the present work we studied the role of Delta like 1
(Dll1) Notch ligand in the differentiation of midbrain dopaminergic neurons. We found that the midbrain of mice lacking Dll1
developed properly just before neurogenesis started. At E10.5 in the ventral region, the number and distribution of cells expressing the
dopaminergic specification genes Foxa2 and Lmx1a was similar to wild-type embryos, but at E11.5 the number of Foxa2+/Lmx1a+
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