The early vertebrates evolved a number of additional
features such as the ability to regulate their body fluids, kidneys homologous
to those of higher vertebrates, additional keratin genes, and more complex
Primitive vertebrates evolved the ability to regulate body osmolarity
unlike primitive craniates in which body fluids had similar ion concentrations
as seawater (Romer, p. 401). In vertebrates, the mesonephros and metanephros
(together called the opistonephros) not segmented after embryonic development
(Romer, p. 405). Nephrons developed collecting ducts and increased the
efficiency of renal secretion and reabsorbion (Hoar, 1969, Vol. I, p.
99). Vertebrate kidneys assumed some of excretory functions performed
by hagfish liver (Hoar, 1969, Vol. I, p. 99).
Vertebrates amplified their number of keratin genes although some of
the primitive vertebrates expressed keratin differently than in higher
vertebrates. (Fuchs, 1981; Markl, 1989). Although lampreys possess glial
cells which are morphologically similar to astrocytes, they lack the intermediate
filaments normally expressed in astrocytes (vimentin and GFAP) and express
keratins. Lamprey glial cells express keratins in both the brain and spinal
cord that are similar to those of the epidermis (Merrick, 1995).
New transcription factors and mechanisms for the control of gene expression
evolved in the first vertebrates such as the duplication of Pax genes(Ogasawara,
2000), the duplication of the Dlx gene(Neidert, 2001; Stock, 1996; Graham,
2002), POU class 3 genes (OMIM), a 5th posterior Hox cluster gene (OMIM;
Marinez, 1999), and a change in the expression pattern of Pax genes in
the pharyngeal arches which may have promoted the formation of jaws (Ogasawara,
There is a conservation of retinoic acid response elements (RAREs) in
vertebrates (Mainguy, 2003).
Clusters of protocadherins are unique to vertebrates (Frank, 2002). The
lamins found in vertebrates possess additional domains and an addition
of 42 amino acids in one ancestral domain. (Reimer, 1998). Lampreys have
a single lactate dehydrogenase gene which has a mixture of characteristics
of the two main LDH genes in higher vertebrates: LDH-A in white skeletal
muscle and LDH-B in aerobic tissues such as the heart and brain (OMIM).
Vertebrates evolved more complex signaling mechanisms. A duplication of
the ancestral gene occurred before lampreys to produce NPY and PYY(Larhammar,
1993). All vertebrates express neuropeptide Y in central and peripheral
nervous systems (Larhammar, 1993). Early in vertebrate evolution, additional
duplications WNT occurred (Sidow, 1992). There are three GnRH genes known
which appear to have resulted from an ancestral gene which was duplicated
in ancestral vertebrates. Two of the three resulting decapeptides have
the same amino acid sequence in all known species. GnRH3 is known only
in fish to date (Fernald, 1999).
Vertebrates utilize small RNA molecules such as 7SK RNP (Bompfunewerer,
2005).and microRNAs (miRNAs) (Bompfunewerer, 2005).