Regional differences in the expression of laminin isoforms during mouse neural tube development

Abstract

Many significant human birth defects originate around the time of neural tube closure or early during post-closure nervous system development. For example, failure of the neural tube to close generates anencephaly and spina bifida, faulty cell cycle progression is implicated in primary microcephaly, while defective migration of neuroblasts can lead to neuronal migration disorders such as lissencephaly. At the stage of neural tube closure, basement membranes are becoming organised around the neuroepithelium, and beneath the adjacent non-neural surface ectoderm. While there is circumstantial evidence to implicate basement membrane dynamics in neural tube and surface ectodermal development, we have an incomplete understanding of the molecular composition of basement membranes at this stage. In the present study, we examined the developing basement membranes of the mouse embryo at mid-gestation (embryonic day 9.5), with particular reference to laminin composition. We performed in situ hybridization to detect the mRNAs of all eleven individual laminin chains, and immunohistochemistry to identify which laminin chains are present in the basement membranes. From this information, we inferred the likely laminin variants and their tissues of origin: that is, whether a given basement membrane laminin is contributed by epithelium, mesenchyme, or both. Our findings reveal major differences in basement composition along the body axis, with the rostral neural tube (at mandibular arch and heart levels) exhibiting many distinct laminin variants, while the lumbar level where the neural tube is just closing shows a much simpler laminin profile. Moreover, there appears to be a marked difference in the extent to which the mesenchyme contributes laminin variants to the basement membrane, with potential contribution of several laminins rostrally, but no contribution caudally. This information paves the way towards a mechanistic analysis of basement membrane laminin function during early neural tube development in mammals.

Laminins and their receptors in the CNS

“…A recent study also examined laminin composition in embryonic brain during neural tube development and identified a unique distribution pattern of various laminin subunits (Copp et al ., ). For example, among all α subunits, laminin‐α1, ‐α3, and ‐α5 are widely expressed at high levels in developing brain (Copp et al ., ). Consistent with these results, laminin‐111 and ‐511 have been identified as the earliest trimeric laminin isoforms expressed during mammalian embryogenesis (Li et al ., ).…”

“…Like laminin-α2, a high level of laminin-α4 is detected in dorsal root ganglia (Miner et al, 1997), cortical plate (Lathia et al, 2007) and endothelial cells (Frieser et al, 1997). In addition, laminin-α5 expression is predominantly found in the neural folds (Copp et al, 2011) and cortical plate (Lathia et al, 2007). Laminin-γ 1, the most common γ subunit, is widely expressed in the CNS.…”

“…For instance, laminin-γ 2 is mainly expressed in epithelial cells (Sugiyama et al, 1995), and laminin-γ 3 expression is detected in cerebellar pia (Li et al, 2012b) and retinal vascular BM (Gersdorff et al, 2005;Li et al, 2012b). A recent study also examined laminin composition in embryonic brain during neural tube development and identified a unique distribution pattern of various laminin subunits (Copp et al, 2011). For example, among all α subunits, laminin-α1, -α3, and -α5 are widely expressed at high levels in developing brain (Copp et al, 2011).…”

Basement Membranes in the Worm

“…For example, the sublateral nerves do not express laminin, but are encased by a basement membrane specifically containing α subunit LAM-3 (Huang et al, 2003). Similar situations have been described in vertebrate tissues, such as the mouse neural tube basement membrane, which contains the laminin α5 subunit that is not expressed by any cells within the neural tube (Copp et al, 2011). Together, these results show that laminin secreted into the extracellular space can be incorporated into basement membranes in a selective manner.…”

Grainyhead-like 2 downstream targets act to suppress epithelial-to-mesenchymal transition during neural tube closure

“…Transmembrane protease serine 2 (TMPRSS2, also known as epitheliasin) is highly expressed in prostate and is involved in EMT regulation in prostate cancer metastasis (Lucas et al, 2014). Laminin gamma 2 (LAMC2) is an epithelial-specific isoform that is highly expressed in many embryonic tissues and adult skin, kidneys and lung, and is found at low levels in a highly invasive prostate cancer cell line (Aumailley and Smyth, 1998;Copp et al, 2011;Drake et al, 2010). LAMC2 helps anchor epithelial cells to the basement membrane (Pulkkinen et al, 1994) and its expression is directly inhibited by the EMTinducing TF ZEB1 (Drake et al, 2010).…”