The medulla oblongata is the caudal portion of the vertebrate hindbrain. It contains major ascending and descending fiber tracts as well as several motor and interneuron populations, including neural centers that regulate the visceral functions and the maintenance of bodily homeostasis. In the avian embryo, it has been proposed that the primordium of this region is subdivided into five segments or crypto-rhombomeres (r7-r11), which were defined according to either their parameric position relative to intersomitic boundaries (Cambronero and Puelles, in J Comp Neurol 427:522-545, 2000) or a stepped expression of Hox genes (Marín et al., in Dev Biol 323:230-247, 2008). In the present work, we examine the implied similar segmental organization of the mouse medulla oblongata. To this end, we analyze the expression pattern of Hox genes from groups 3 to 8, comparing them to the expression of given cytoarchitectonic and molecular markers, from mid-gestational to perinatal stages. As a result of this approach, we conclude that the mouse medulla oblongata is segmentally organized, similarly as in avian embryos. Longitudinal structures such as the nucleus of the solitary tract, the dorsal vagal motor nucleus, the hypoglossal motor nucleus, the descending trigeminal and vestibular columns, or the reticular formation appear subdivided into discrete segmental units. Additionally, our analysis identified an internal molecular organization of the migrated pontine nuclei that reflects a differential segmental origin of their neurons as assessed by Hox gene expression.

We have tested the usefulness of several commercial anti-CD33 monoclonal antibodies (mAb) to determine the expression and localization of the two CD33 isoforms on several hematopoietic cell lines. The expression of the isoform CD33m, a CD33 transmembrane splice variant lacking the ligand-binding V immunoglobulin (Ig)-like domain, was detected by RT-polymerase chain reaction, western blot, confocal microscopy and flow cytometry on the membrane of several human cell types. CD33m was only detected by the anti-CD33 mAb HIM3-4 on the cell surface, whereas WM53, P67.6, 4D3, HIM3-4, WM54, D3HL60.251 or MY9 detected the CD33M isoform, indicating that HIM3-4 is the only mAb recognizing CD33 C(2) Ig domain. Accordingly, HIM3-4 binding to CD33 did not interfere with the binding of other antibodies against the CD33 V-domain. P67.6 mAb interfered with recognition by the rest of antibodies specific for the V domain. HIM3-4 staining could be increased after the sialidase treatment of all CD33(+) cells. However, this increase was stronger in activated T cells, suggesting a CD33 masking state in this cell population. Confocal microscopy analysis of CD33m HEK 293T-transfected cells revealed that this protein is expressed on the cell membrane and also detected in the Golgi compartment. CD33 is constitutively located outside the lipid raft domains, whereas cross-linked CD33 is highly recruited to this signaling platform. The unique ability of HIM3-4 mAb to detect the masking state of CD33 on different cell lineages makes it a good tool to improve the knowledge of the biological role of this sialic acid-binding Ig-like lectin.

The interpeduncular nucleus (IP) is a key limbic structure, highly conserved evolutionarily among vertebrates. The IP receives indirect input from limbic areas of the telencephalon, relayed by the habenula via the fasciculus retroflexus. The function of the habenulo-IP complex is poorly understood, although there is evidence that in rodents it modulates behaviors such as learning and memory, avoidance, reward and affective states. The IP has been an important subject of interest for neuroscientists, and there are multiple studies about the adult structure, chemoarchitecture and its connectivity, with complex results, due to the presence of multiple cell types across a variety of subnuclei. However, the ontogenetic origins of these populations have not been examined, and there is some controversy about its location in the midbrain-anterior hindbrain area. To address these issues, we first investigated the anteroposterior (AP) origin of the IP complex by fate-mapping its neuromeric origin in the chick, discovering that the IP develops strictly within isthmus and rhombomere 1. Next, we studied the dorsoventral (DV) positional identity of subpopulations of the IP complex. Our results indicate that there are at least four IP progenitor domains along the DV axis. These specific domains give rise to distinct subtypes of cell populations that target the IP with variable subnuclear specificity. Interestingly, these populations can be characterized by differential expression of the transcription factors Pax7, Nkx6.1, Otp, and Otx2. Each of these subpopulations follows a specific route of migration from its source, and all reach the IP roughly at the same stage. Remarkably, IP progenitor domains were found both in the alar and basal plates. Some IP populations showed rostrocaudal restriction in their origins (isthmus versus anterior or posterior r1 regions). A tentative developmental model of the structure of the avian IP is proposed. The IP emerges as a plurisegmental and developmentally heterogeneous formation that forms ventromedially within the isthmus and r1. These findings are relevant since they help to understand the highly complex chemoarchitecture, hodology and functions of this important brainstem structure.

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