Biology subjects

Rickabaugh, M. K.

Publications and source records attributed to Rickabaugh, M. K..

2 recordsLinked to original sources

bioRxiv2022

Novel insights into the fundamentals of palatal shelf elevation dynamics in normal mouse embryos

Embryonic palate development involves bilateral vertical growth of palatal shelves - extensions from the maxillary processes - next to the tongue until embryonic day (E) 13.5. Following vertical growth, palatal shelves elevate and adhere above the tongue by E14.5. Current models indicate that this process of elevation involves a complex vertical to horizontal reorienting of the palatal shelves. While earlier studies have implied that this is a rapid process, the precise timing has not been resolved. To understand the dynamics of palatal shelf elevation, we employed time-restricted pregnancies with a one-hour resolution and magnetic resonance imaging of intermediate stages. Our data showed that in almost all C57BL/6J embryos, palatal shelves have not yet elevated by E14.0. However, six hours later at E14.25, palatal shelves have completed elevation in 80% of embryos. Interestingly, all E14.25 embryos with unelevated palatal shelves (20%) were female, suggesting a delay in female embryos. In FVB/NJ embryos, the elevation window started earlier (E13.875-E14.25) without any noticeable sex differences. We frequently captured an intermediate stage with unilateral elevation of either right or left palatal shelf. Magnetic resonance imaging of various stages showed that palatal shelf elevation began with the formation of bilateral bulges in the posterior. These bulges progressed laterally and anteriorly over time. During elevation, we observed increased cell proliferation in the lingual region of the palatal shelf. Within the bulge, cell orientation was acutely tilted towards the tongue and actomyosin activity was increased, which together may participate in the projection of the bulge in the horizontal direction. Thus, our data reveal novel insights into the rapid dynamic changes in palatal shelf elevation that lay the foundation for future studies of normal and abnormal palatogenesis.

developmental biology↗

bioRxiv2021

In-frame deletion of SPECC1L microtubule binding domain results in embryonic tissue movement and fusion defects

Embryonic morphogenesis of the neural tube, palate, ventral body wall and optic fissure require precise sequence of tissue movement and fusion, which if incomplete, leads to anencephaly/exencephaly, cleft palate, omphalocele and coloboma, respectively. These are genetically heterogeneous birth defects, so there is a continued need to identify etiologic genes. Patients with autosomal dominant SPECC1L mutations show syndromic malformations, including hypertelorism, cleft palate and omphalocele. These SPECC1L mutations cluster in the second coiled-coil domain (CCD2), which facilitates association with microtubules. To study SPECC1L function in mice, we first generated a null allele (Specc1l{Delta}Ex4) lacking the entire SPECC1L protein. Homozygous mutants for these truncations died perinatally without cleft palate or exencephaly. Given the clustering of human mutations in CCD2, we hypothesized that targeted perturbation of CCD2 may be required. Indeed, homozygotes for in-frame deletions involving CCD2 (Specc1l{Delta}CCD2) resulted in ~50% exencephaly and ~50% cleft palate. Interestingly, these two phenotypes are never observed in the same embryo. Examination of embryos with and without exencephaly revealed that the oral cavity was narrower in exencephalic embryos, which allowed palatal shelves to elevate despite their defect. In contrast to an evenly distributed subcellular expression pattern, mutant SPECC1L-{Delta}CCD2 protein showed abnormal subcellular localization, decreased overlap with microtubules, increased actin bundles, and dislocated non-muscle myosin II to the cell cortex. Thus, we show that perturbations of CCD2 in the context of full SPECC1L protein affects tissue fusion dynamics, indicating that human SPECC1L CCD2 mutations are gain-of-function. Improper SPECC1L subcellular localization appears to disrupt connections between actomyosin and microtubule networks, which in turn may affect cell alignment and coordinate movement during tissue morphogenesis.

developmental biology↗