  Spectroscopic studies of low-luminosity early-type galaxies are essential to
understand their origin and evolution but remain challenging because of low
surface brightness levels. We describe an observational campaign with the new
high-throughput Binospec spectrograph at the 6.5-m MMT. It targets a
representative sample of dwarf elliptical (dE), ultra-diffuse (UDG), and dwarf
spheroidal (dSph) galaxies. We outline our data analysis approach that features
(i) a full spectrophotometric fitting to derive internal kinematics and star
formation histories of galaxies; (ii) two-dimensional light profile
decomposition; (iii) Jeans anisotropic modelling to assess their internal
dynamics and dark matter content. We present first results for 9 UDGs in the
Coma cluster and a nearby dSph galaxy, which suggest that a combination of
internal (supernovae feedback) and environmental (ram-pressure stripping,
interactions) processes can explain observed properties of UDGs and, therefore,
establish an evolutionary link between UDGs, dSph, and dE galaxies.
