Callosal septa express guidance cues and are paramedian guideposts for human corpus callosum development

Abstract

The early development and growth of the corpus callosum are supported by several midline transient structures in mammals that include callosal septa (CS), which are present only in the second half of gestation in humans.Here we provide new data that support the guidance role of CS in corpus callosum development, derived from the analysis of 46 postmortem fetal brains, ranging in age from 16 to 40 post conception weeks (PCW). Using immunohistochemical methods, we show the expression pattern of guidance cues ephrinA4 and neogenin, extracellular protein fibronectin, as well as non-activated microglia in the CS. We found that the dynamic changes in expression of guidance cues, cellular and extracellular matrix constituents in the CS correlate well with the growth course of the corpus callosum at midsagittal level. The CS reach and maintain their developmental maximum between 20 and 26 PCW and can be visualized as hypointense structures in the ventral callosal portion with ex vivo (in vitro) T2-weighted 3T magnetic resonance imaging (MRI). The maximum of septal development overlaps with an increase in the callosal midsagittal area, whereas the slow, gradual resolution of CS coincides with a plateau of midsagittal callosal growth. The recognition of CS existence in human fetal brain and the ability to visualize them by ex vivo MRI attributes a potential diagnostic value to these transient structures, as advancement in imaging technologies will likely also enable in vivo MRI visualization of the CS in the near future.

Development of human white matter pathways in utero over the second and third trimester

“…Developing callosal fibers grow through complex pathways and cross the midline using different substrates in transient fetal structures such as the callosal septa. The callosal septa are prominent between 18 and 34 wk, and their biochemical composition is dynamically over this period, including changes in the expression of axonal guidance molecules, cellular matrix, and ECM constituents, which are likely to affect tensor metrics (64,65). Previous studies have also identified differences in the growth rate of different sections of the CC, with the genu growing at a faster rate than the body and the splenium during fetal development, but then after birth, mature myelination is observed in the splenium before the genu (55,51,66,67).…”

Constitutive activation of canonical Wnt signaling disrupts choroid plexus epithelial fate

“…Sections were then incubated with primary antibodies for 48 h at 4 ˚C (AXIN2 1:100, FZD1 1:100, LEF1 1:100, AQP1 1:100, OTX2 1:50, β-Catenin cell signaling 1:400, β-Catenin Dako 1:200), washed and subsequently incubated with secondary antimouse or antirabbit antibodies diluted in PBS (at 1:1000) for 2 h at the room temperature. For visualization of the specific immune reactivity following secondary antibodies were used according to the laboratory protocol 63 : the donkey antimouse IgG Alexa fluor-plus 488, donkey antirabbit IgG Alexa fluor-plus 647, donkey antirabbit IgG 488, donkey antimouse IgG Alexa fluor 546 were used. Sections were covered with a mounting medium containing DAPI.…”

The Signature of Moderate Perinatal Hypoxia on Cortical Organization and Behavior: Altered PNN-Parvalbumin Interneuron Connectivity of the Cingulate Circuitries

“…The brain structure was analyzed on coronal sections, cryo-sections 60 µm thick for P1, and paraffin 14 µm thick for P105, stained by cresyl-violet (modification by Nissl: 0.5% Cresyl violet, Chemika, Girraween, NSW, Australia). The differential expression of specific proteins was examined by immunofluorescent (IF; free-floating 60 μm thick cryo-sections for P1; glass-mounted 14 µm thick sections for P105) and classic non-fluorescent (IHC) (free-floating 60 μm thick cryo-sections for P1; glass-mounted 14 µm thick sections for P105) staining as described in our previous publications ( Bobić Rasonja et al, 2019 ; Culjat and Milošević, 2019 ), and given in more details in the Supplementary Material .…”